ChemWiki - User contributions [en]

User:Ew914

2017-02-10T11:46:44Z

Ew914: /* Conclusion */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOS EX1.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. The activation energy is lower for the endo diels-alder transition state which also shows greater stabilisation than for the exo-diels-alder reaction. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|161
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction and produced the thermodynamic product due to a greater level of stabilisation due to a more negative gibbs free energy. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:42:54Z

Ew914:

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOS EX1.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. The activation energy is lower for the endo diels-alder transition state which also shows greater stabilisation than for the exo-diels-alder reaction. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|161
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:39:57Z

Ew914: /* MO Diagram and MOs */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOS EX1.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|161
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:38:54Z

Ew914: /* MO Diagram and MOs */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOS EX1.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-72</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|161
|<nowiki>-68</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:32:57Z

Ew914: /* MO Diagram */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOS EX1.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

File:MOS EX1.JPG

2017-02-10T11:32:36Z

Ew914:

User:Ew914

2017-02-10T11:17:32Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy but is the most stabilised which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:16:02Z

Ew914: /* Conclusion */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy and the largest gibbs free energy which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions which do not exist in the exo diels-alder reaction. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:13:56Z

Ew914:

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy and the largest gibbs free energy which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

In these exercises, guassian was used to study the energy and pathways of various reactions. Exercise 1 confirmed that diels-alder reactions are synchronous and a reaction can only occur between orbitals of the same symmetry. Bond formation occurs when the distance between the bonds is smaller than the sum of the van der waals radii of the atoms. Exercise 2 studied the differences between endo- and exo- diels-alder pathways. The exo diels-alder reaction yielded the thermodynamic product because of the high gibbs free energy whereas the endo diels-alder reaction produced the kinetically stabilized product due to the lower activation energy caused by the secondary orbital interactions. Exercise 3 showed that a reaction can also proceed via a cheletropic reaction under thermodynamic conditions.

User:Ew914

2017-02-10T11:02:37Z

Ew914:

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy and the largest gibbs free energy which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==

User:Ew914

2017-02-10T11:01:00Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC, a partial double bond is formed in the xylene, then the C-O and C-S sigma bonds are formed and then the partial double bond and SO2 is formed to complete the reaction and produce a stable aromatic product.

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25. The cheletropic reaction has the largest activation energy and the largest gibbs free energy which means it is the thermodynamic product. The endo diels-alder reaction has the lowest activation energy which means it is the kinetic product. The exo diels-alder reaction has a higher activation energy and higher gibbs free energy than the endo pathway but is not the preferred route under kinetic or thermodynamic control.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

<nowiki>==Conclusion==</nowiki>

User:Ew914

2017-02-10T10:48:12Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

The reaction between xylene and SO2 can take place via a cheletropic reaction, an endo diels-alder reaction or an exo diels-alder reaction. The reaction scheme is shown in figure 23.

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

An IRC calculation for each pathway along with the animation is shown in figure 24. Xylene is unstable and very reactive because it contains a large number of double bonds and is not aromatic. Looking at the IRC

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

A reaction profile containing the energy levels of the reactants, transition states and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction is shown in figure 25.

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==|}

User:Ew914

2017-02-10T10:25:13Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

The MOs for the HOMO and LUMO of cyclohexadiene, 1,3-dioxole and the exo- and endo- transition states are shown in Figures 14-21.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==|}

User:Ew914

2017-02-10T10:23:25Z

Ew914: /* MO Diagram and MOs */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Secondary.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==|}

File:Secondary.JPG

2017-02-10T10:23:00Z

Ew914:

User:Ew914

2017-02-10T10:20:42Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

==Introduction==

The potential energy surface illustrates the energy of a system as a function of two or more coordinates. If there is only one coordinate, it is called a potential energy curve. Two key characteristics of a potential energy surface are called the transition state and the minimum. The transition state is the highest potential energy species along a reaction profile whereas the mimimum is the lowest potential energy species along a reaction profile. Both of these species are turning points on the curve and therefore the gradient is 0.

For this computational lab, gaussian was used along with two electronic structure methods to locate and study the transition states of reactions by calculating the energy and reaction paths of the reactants, products and transitions states of various reactions.

==Exercise 1: Reaction of Butadiene with Ethylene==

The reaction between butadiene and ethylene is a Diels–Alder reaction or a [4+2] cycloaddition to form cyclohexene. The reaction scheme is shown in Figure 1.

[[File:Reaction_scheme.PNG|thumb|1000px|Figure 1: The Reaction Scheme showing the reaction between butadiene and ethylene|center]]

===MO Diagram===

The MO Diagram for the formation of the butadiene and ethylene transition state is shown in Figure 2. The symmetry of the orbitals is labeled as either symmetric, s or asymmetric, a.

[[File:MO diagram.jpg|thumb|1000px|Figure 2: The MO Diagram for the formation of the butadiene/ethylene TS|center]]

The MOs for the HOMO and LUMO of butadiane, ethylene and the transition state are shown in Figures 3-8.

[[File:MOs Total EW.JPG|thumb|1000px|center]]

A reaction is 'allowed' when the symmetry labels of the orbitals are the same and when the symmetry labels are not the same, the reaction is 'forbidden.' For both a symmetric-symmetric interaction and an asymmetric-asymmetric interaction the overlap integral is non-zero whereas the overlap integral is zero for a symmetric-asymmetric interaction.

===Bond Length Measurements===

The measurements of the 4 C-C bond lengths of the reactants and the 6 C-C bond lengths of the transition state and the products is shown in Figure 9. As the reaction progresses, a change in bond length can be observed. The double bonds of the reactants increase in bond length from around 1.3 Å to 1.5 Å, whereas the single bond of the reactants decreased in bond length from around 1.3 Å to 1.5 Å.

[[File:Bond lengths.jpg|thumb|1000px|Figure 9: The Bond Length Measurements for the Reactants, Transition State and Product|center]]

Figure 10 shows the typical C-C bond lengths at different levels of hybridization and the bond lengths from this reaction are in agreement with those bond lengths. The Van der Waals radius of a C atom is 1.70 Å and the partly formed C-C bond length in the transition state is 2.115Å. This confirms that there are bonding interactions between the terminal carbons of the butadiene and the carbons of the ethylene because 2.115 Å is less than 2 x 1.70 Å.

[[File:Hybrid1.PNG|thumb|1000px|Figure 10: Typical Bond Lengths for C-C bonds at various hybridizations|center]]

===Reaction Path at the Transition State Vibration===

Figure 11 shows the reaction path at the transition state which corresponds to the frequency at -526.83 cm-1. This is a synchronous formation of the two bonds.

[[File:Transition State vibration.gif|thumb|500px|center|Figure 11. Transition State Vibration]]

==Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole==

Cyclohexadiene and 1,3-dioxole react in a diels-alder reaction as shown in figure 12.

[[File:Reaction scheme.jpg|thumb|1000px|Figure 12: The Reaction Scheme showing the reaction of Cyclohexadiene and 1,3-Dioxole |center]]

===MO Diagram and MOs===

A molecular orbital diagram was constructed as shown in figure 13. The oxygen lone pair increases the energy levels of the 1,3-dioxole compared with ethylene. This includes the raising of the HOMO of dioxole which means that it now reacts better with the LUMO of cyclohexadiene because the orbitals are closer in energy.

[[File:MO diagramwer.jpg|thumb|1000px|Figure 13: The MO Diagram of the Diels-Alder reaction between Cyclohexadiene and 1,3-Dioxole |center]]

In diels-alder reactions, normal demand or inverse demand can occur. Normal demand is favoured by an electron poor dienophile and an electron rich diene whereas inverse demand occurs when there is an electron rich dienophile and an electron rich diene which involves the overlap of the HOMO of the dienophile with the unoccupied MO of the diene. The increase in energy of the HOMO and LUMO of the dienophile or 1,3 dioxole due to the oxygen lone pair means that the overlap between the dioxole HOMO and cyclohexadiene LUMO (inverse demand) is better than the overlap between the cyclohexadiene HOMO and dioxole LUMO (normal demand), concluding that this is an inverse demand diels-alder reaction.

[[File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG|thumb|1000px|center]]
[[File:Exercise 2 MOs EWWWW.JPG|thumb|1000px|center]]

As shown in figure 22, secondary orbital reactions can be seen between the lone pair on the oxgyen and the π* orbital for the endo diels-alder transition state. There is no secondary orbital interaction between the oxygen lone pair and the π* orbital in the exo diels-alder transition state.

[[File:Orbital interactionerw.JPG|thumb|1000px|Figure 22: Secondary Orbital interaction in the exo and endo transition states |center]]

The table below shows the obtained activation energies and gibbs free energies for both the endo and exo diels-alder reactions. Both the activation energy and gibbs free energy are lower for the endo diels-alder transition state. With regards to sterics, there is less steric hinderance in the endo transition state than in the exo transition state which aligns with the lower activation energy of the endo transition state. This confirms that the endo diels-alder reaction is both the thermodynamic product and the kinetic product.

{| class="wikitable"
!
!Reactants (KJ/mol)
!Transition State (KJ/mol)
!Product (KJ/mol)
!Ea (KJ/mol)
!ΔG (KJ/mol)
|-
|Exo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313364</nowiki>
|<nowiki>-1313601</nowiki>
|169
|<nowiki>-68</nowiki>
|-
|Endo
|<nowiki>-1313533</nowiki>
|<nowiki>-1313372</nowiki>
|<nowiki>-1313605</nowiki>
|169
|<nowiki>-72</nowiki>
|+Table showing the activation and reaction energies of the reactants, the transition state and the products for endo and exo diels-alder reaction between Cyclohexadiene and 1,3-Dioxole
|}

==Exercise 3: Diels-Alder vs Cheletropic==

[[File:Reaction Scheme ex3ew.jpg|thumb|1000px|center|Figure 23. Reaction Scheme Showing the Different Pathways for an o-Xylylene-SO2 Cycloaddition]]

{| class="wikitable" border="1"
|+ Figure 24: Table showing the reaction coordinate with an IRC calculation for each path
| Exo Diels-Alder Reaction || [[File:Exo ew IRC movie.gif|thumb|500px|center]] || [[File:Exo ew IRC image.jpg|thumb|500px|center]]
|-
| Endo Diels-Alder Reaction || [[File:ENDO IRC movie.gif|thumb|500px|center]] || [[File:ENDO EW IRC image.jpg|thumb|500px|center]]
|-
| Cheletropic Reaction || [[File:ChelIRC Reaction movie.gif|thumb|500px|center]] || [[File:IRC image.jpg|thumb|500px|center]]
|}

[[File:Activation energy diagramerwww.jpg|thumb|1000px|center|Figure 25. A Reaction Profile for the endo- and exo- Diels-Alder reactions and the cheletropic reaction for a reaction between Xylylene and SO2]]

==Conclusion==|}

User:Ew914

2017-02-10T10:00:15Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

User:Ew914

2017-02-09T23:20:32Z

Ew914: /* Activation and Reaction Energies */

User:Ew914

2017-02-09T23:18:00Z

Ew914: /* Activation and Reaction Energies */

User:Ew914

2017-02-09T23:16:49Z

Ew914: /* Activation and Reaction Energies */

User:Ew914

2017-02-09T23:09:34Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

User:Ew914

2017-02-09T23:07:35Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

File:Activation energy diagramerwww.jpg

2017-02-09T23:04:03Z

Ew914:

User:Ew914

2017-02-09T22:19:59Z

Ew914: /* Activation and Reaction Energies */

User:Ew914

2017-02-09T22:18:38Z

Ew914: /* Activation and Reaction Energies */

User:Ew914

2017-02-09T22:16:21Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

User:Ew914

2017-02-09T21:13:47Z

Ew914: /* MO Diagram and MOs */

File:Orbital interactionerw.JPG

2017-02-09T21:12:28Z

Ew914:

File:Orbital interaction.JPG

2017-02-09T21:12:02Z

Ew914: Ew914 uploaded a new version of File:Orbital interaction.JPG

User:Ew914

2017-02-09T21:04:51Z

Ew914: /* MO Diagram and MOs */

File:Exercise 2 MOs EWWWW232323fdgfdgfdgfd.JPG

2017-02-09T21:04:36Z

Ew914:

User:Ew914

2017-02-09T21:03:45Z

Ew914: /* MO Diagram and MOs */

File:Exercise 2 MOs EWWWW232323.JPG

2017-02-09T21:03:33Z

Ew914:

File:Exercise 2 MOs EWWWW.JPG

2017-02-09T21:03:01Z

Ew914: Ew914 uploaded a new version of File:Exercise 2 MOs EWWWW.JPG

File:Exercise 2 MOs EWWWW.JPG

2017-02-09T21:02:56Z

Ew914:

User:Ew914

2017-02-09T20:41:11Z

Ew914: /* MO Diagram and MOs */

User:Ew914

2017-02-09T20:40:54Z

Ew914: /* MO Diagram */

File:Exercise 2 MOs EW.JPG

2017-02-09T20:40:31Z

Ew914:

User:Ew914

2017-02-09T19:53:28Z

Ew914: /* MO Diagram */

User:Ew914

2017-02-09T19:52:19Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

File:MO diagramwer.jpg

2017-02-09T19:51:41Z

Ew914:

File:MO diagramerw.jpg

2017-02-09T19:50:42Z

Ew914:

User:Ew914

2017-02-09T17:16:33Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

User:Ew914

2017-02-09T17:16:16Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

User:Ew914

2017-02-09T17:15:27Z

Ew914: /* Exercise 2: Reaction of Cyclohexadiene and 1,3-Dioxole */

User:Ew914

2017-02-09T17:15:12Z

Ew914:

File:Reaction scheme.jpg

2017-02-09T17:12:57Z

Ew914: Ew914 uploaded a new version of File:Reaction scheme.jpg

reaction scheme

User:Ew914

2017-02-09T16:36:27Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

User:Ew914

2017-02-09T16:36:10Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */

User:Ew914

2017-02-09T16:34:48Z

Ew914: /* Exercise 3: Diels-Alder vs Cheletropic */