File:Exo IRC cyy.png

2017-03-24T11:26:46Z

Yc9014:

File:Endo IRC cyy.png

2017-03-24T11:26:04Z

Yc9014:

2017-03-24T10:38:29Z

Yc9014: /* Exercise 2:Reaction of Cyclohexadiene and 1,3-Dioxole */

== Introduction ==

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

HOMO and LUMO of both reactants can be visualized by GaussiView and shown in '''table 1''' as following.

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cis''-Butadiene
|[[File:Diene_HOMO_cyy.jpg|250px]]
|[[File:Diene_LUMO_cyy.jpg|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|Ethylene
|[[File:Ethene_HOMO_cyy.jpg|250px]]
|[[File:Ethene_LUMO_cyy.jpg|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

After the transition state was optimized and its identity proved by IRC, graph of the energy levels proceed from HOMO and LUMO of the reactants was visualized and shown in '''table 2'''.

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the reaction of butadiene and ethylene
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_16_as.jpg|344x344px]]
|[[image:Level_17_s.jpg|344x344px]]
|[[image:Level_18_s.jpg|344x344px]]
|[[image:Level_19_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

From the graphs in '''table 2'''

HOMO-1 is a in-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS),

HOMO is a in-phase combination of butadiene LUMO(S) and ethylene HOMO(S),

LUMO is a anti-phase combination of butadiene LUMO(S) and ethylene HOMOMO(S),

LUMO+1 is a anti-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS)

With these combination relationship and relative energy levels above, a MO diagram can be drawn as '''graph 1'''.

[[image:MO-1.jpg|thumb|center|Graph 1. MO diagram of transition state.]]

As indicated from the graph,the symmetry of two potential reacting orbitals must match with each other. ie. symmetric orbital interacts with symmetric orbital, asymmetric orbital interacts with asymmetric orbitals.
The orbital overlap can only be none-zero when the two orbitals have the same symmetry.For symmetrically mismatched orbitals(symmetric with asymmetric), no overlap means no interaction, therefore, no reaction happen.

{| class="wikitable" border="1"
|+ table 3
! symmetry interaction !! Orbital overlap integral
|-
| AS-AS || None-zero
|-
| AS-S || zero
|-
| S-S || none-zero
|}

'''bond length'''

[[image:Internuclear_distance_new.png|thumb|left|graph 2. Inter-nuclear distances of butadiene react with ethylene.|711x711px]]
[[image:Bond_distances_indicator.jpg|thumb|Graph 3. Carbon positions.|590x590px|none]]

{| class="wikitable" border="1"
|+ typical bond length
! bond !! bond length(Å)
|-
| sp3-sp3 || 1.54
|-
| sp3–sp2 || 1.50
|-
| sp2–sp2 || 1.47
|-
| benzene || 1.40
|-
| alkene || 1.34
|}

As can see from '''graph 2''' , the bond length of the double bond in butadiene and ethylene decreases and the single bond in butadiene experiences a increase in bond length while two new bonds forms between two molecules.
The Van der Waals radius of the C atom is 1.70.
the partly form C-C has a bond length longer than normal sp3-sp3 single bond.

'''Illustrate the vibration that corresponds to the reaction path at the transition state. Is the formation of the two bonds synchronous or asynchronous?'''

Two bonds form synchronously.

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

'''Using your MO diagram for the Diels-Alder reaction, locate the occupied and unoccupied orbitals associated with the DA reaction for both TSs by symmetry. Find the relevant MOs and add them to your wiki (at an appropriate angle to show symmetry). Construct a new MO diagram using these new orbitals, adjusting energy levels as necessary. '''

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cyclohexdiene
|[[File:Cyclohexdiene_HOMO_as.png|250px]]
|[[File:Cyclohexdiene_LUMO_s.png|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|dioxole
|[[File:Dioxle_HOMO_s.png|250px]]
|[[File:Dioxole_LUMO_as.png|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of endo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:HOMO-1_as.jpg|344x344px]]
|[[image:HOMO_s.jpg|344x344px]]
|[[image:LUMO_s.jpg|344x344px]]
|[[image:LUMO+1_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the exo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_29_as.jpg|344x344px]]
|[[image:Level_30_s.jpg|344x344px]]
|[[image:Level_31_as.jpg|344x344px]]
|[[image:Level_32_s.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Anti-ymmetric (AS)
|Symmetric (S)
|}

It can been seen from the graph that endo product has the same orbital symmetry order (AS/S/S/AS from LUMO-1 to HOMO +1) with the the cyclohexene formation in exercise one, so it has a similar MO diagram with as graph**. However, the exo transition state has a different orbital symmetry order(AS /S/AS/S from LUMO-1 to HOMO). So the MO diagram is adjusted as following graph.

[[image:Exo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog exo reaction.]]
[[image:Endo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog endo reaction.]]

It is an inverse DA reactions. A normal DA reaction happen between a electron-poor dienophile and an electron rich diene. An inverse DA happen between an electron-rich dienophile and an electron-poor diene. In the case, the diene is not very electron poor nor electron rich, but dienophile 1,3-Dioxole is very electron rich due to direct attach to two electron donating oxygen atom. The orbital energy rises in dienophile and HOMO of dienolphile interact with LUMO of diene and form most energetically favored new orbital

'''In the .log files for each calculation, find a section named "Thermochemistry". Tabulate the energies and determine the reaction barriers and reaction energies (in kJ/mol) at room temperature (the corrected energies are labelled "Sum of electronic and thermal Free Energies", corresponding to the Gibbs free energy). Which are the kinetically and thermodynamically favourable products? '''

At room temperature,1 Hartree= 627.509 kcal mol-1

energy for Cyclohexadiene,0.118067. energy for 1,3-Dioxole -0.052286. Energy for reatant=(0.118067-0.052286)<math>\times</math>627.509kcal mol-1=41.27 kJ mol-1

energy for endo transition state, 0.137943<math>\times</math>627.509kcal mol-1=86.56 kJ mol-1
energy for endo product,0.037803<math>\times</math>627.509kcal mol-1=23.72 kJ mol-1

energy for exo transition state, 0.138903<math>\times</math>627.509kcal mol-1=87.16 kJ mol-1
energy for exo product,0.037975<math>\times</math>627.509kcal mol-1=23.83 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo
|45.89
|<math>-17.44</math>
|-
|endo
|45.29
|<math>-17.55</math>
|}

[[image:Exercise_2_reaction_coordinate.jpg|thumb|center|Graph **. reaction coordinate of endo and exo DA reaction.]]
The calculation shows that endo product are both kinetic and thermo product. Endo product is the kinetic product because of the secondary effect. as can be seen from the graph below, the two middle orbitals on diene can interact with the orbital from oxygen
[[image:Secondary_effect.jpg|thumb|center|Graph **. reaction coordinate of endo and exo DA reaction.]]

''ADD REFERENCE''

In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction. Thus, only the reaction between the HOMO of cyclopentadiene and the LUMO of maleic anhydride is allowed. Furthermore, though the exo-product is the more thermodynamically stable isomer, there are secondary (non-bonding) orbital interactions in the endo- transition state, lowering its energy and making the reaction towards the endo- product faster, and therefore more kinetically favorable. Since the exo-product has primary (bonding) orbital interactions it can still form, but since the endo-product forms faster it is the major product.

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

'''2) Visualise the reaction coordinate with an IRC calculation for each path. Include a .gif file in the wiki of these IRCs.'''

{| class="wikitable"
! colspan="3" |Table 4. reaction coordinate for three routes
|-
!cheletropic product
!exo
!endo
|-
|[[File:Exercise_3_cheletropic.gif|550px]]
|[[File:Exercise_3_endo.gif|550px]]
|[[File:Exercise_3_exo.gif|550px]]
|}

'''3) Calculate the activation and reaction energies (converting to kJ/mol) for each step as in Exercise 2 to determine which route is preferred.'''

At room temperature

The energy measurement in GaussView is in Hartree,
1 Hartree= 627.509 kcal mol-1

energy for so2, -0.118614.energy for xylyene,0.178554. Energy of the reactants=(-0.118614+0.178554)<math>\times</math>627.509kcal mol-1=37.61 kJ mol-1

energy for exo 6-membered-ring TS, 0.092079<math>\times</math>627.509kcal mol-1=57.78 kJ mol-1

energy for exo 6-membered-ring product, 0.056109<math>\times</math>627.509kcal mol-1=35.21 kJ mol-1

energy for endo 6-membered-ring TS, 0.090559<math>\times</math>627.509kcal mol-1=56.83 kJ mol-1

energy for endo 6-memberd-ring product, 0.021700<math>\times</math>627.509kcal mol-1=13 kJ mol-1

energy for 5-memberd-ring TS, 0.099060<math>\times</math>627.509kcal mol-1=62.16 kJ mol-1

energy for 5-memberd-ring product, -0.000002<math>\times</math>627.509kcal mol-1=-0.0012 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo 6-membered-ring
|20.17
|<math>-2.4</math>
|-
|endo 6-membered-ring
|19.22
|<math>-24.61</math>
|-
|5-memberd-ring
|24.55
|<math>-37.61</math>
|}

The endo Diels-Alder product is kinetically preferred as it has lowest activation energy.
The cheletropic product is aerodynamically preferred as it has lowest reaction energy.

'''4) Using Excel or Chemdraw, draw a reaction profile that contains relative heights of the energy levels of the reactants, TSs and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction. You can set the 0 energy level to the reactants at infinite separation.'''

[[image:New_MO_coordinate.jpg|thumb|center|reaction coordinate of three product.|344x344px]]
As can be seen in the graph. cheletropic product has the lowest energy so it is thermodynamic product. Endo product is the kinetic product.

'''Xylylene is highly unstable. Look at the IRCs for the reactions - what happens to the bonding of the 6-membered ring during the course of the reaction?'''

[[image:IRC_cheletropic_bond.png|530x530px]]
[[image:IRC_endo_bond.png|530x530px]]
[[image:IRC_exo_bond.png|530x530px]]

As can be seen from the graph, all nbond lengths changed. Two double bond on the ring extends and sing bonds shortens and finally all of they reaches a similar distances as the electron density delocalise in the 6 membered ring. The graph of endo and exo product are similar as they share the same structure. Cheletropic product has one bond slightly long than other. This is because the bond is shared with the neighboring 5 membered ring and experience a additional ring strain.

== Conclusion ==

File:Secondary effect.jpg

2017-03-24T10:30:46Z

Yc9014:

Rep:Yc9014-transition

2017-03-24T10:21:35Z

Yc9014: /* Exercise 2:Reaction of Cyclohexadiene and 1,3-Dioxole */

== Introduction ==

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

HOMO and LUMO of both reactants can be visualized by GaussiView and shown in '''table 1''' as following.

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cis''-Butadiene
|[[File:Diene_HOMO_cyy.jpg|250px]]
|[[File:Diene_LUMO_cyy.jpg|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|Ethylene
|[[File:Ethene_HOMO_cyy.jpg|250px]]
|[[File:Ethene_LUMO_cyy.jpg|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

After the transition state was optimized and its identity proved by IRC, graph of the energy levels proceed from HOMO and LUMO of the reactants was visualized and shown in '''table 2'''.

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the reaction of butadiene and ethylene
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_16_as.jpg|344x344px]]
|[[image:Level_17_s.jpg|344x344px]]
|[[image:Level_18_s.jpg|344x344px]]
|[[image:Level_19_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

From the graphs in '''table 2'''

HOMO-1 is a in-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS),

HOMO is a in-phase combination of butadiene LUMO(S) and ethylene HOMO(S),

LUMO is a anti-phase combination of butadiene LUMO(S) and ethylene HOMOMO(S),

LUMO+1 is a anti-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS)

With these combination relationship and relative energy levels above, a MO diagram can be drawn as '''graph 1'''.

[[image:MO-1.jpg|thumb|center|Graph 1. MO diagram of transition state.]]

As indicated from the graph,the symmetry of two potential reacting orbitals must match with each other. ie. symmetric orbital interacts with symmetric orbital, asymmetric orbital interacts with asymmetric orbitals.
The orbital overlap can only be none-zero when the two orbitals have the same symmetry.For symmetrically mismatched orbitals(symmetric with asymmetric), no overlap means no interaction, therefore, no reaction happen.

{| class="wikitable" border="1"
|+ table 3
! symmetry interaction !! Orbital overlap integral
|-
| AS-AS || None-zero
|-
| AS-S || zero
|-
| S-S || none-zero
|}

'''bond length'''

[[image:Internuclear_distance_new.png|thumb|left|graph 2. Inter-nuclear distances of butadiene react with ethylene.|711x711px]]
[[image:Bond_distances_indicator.jpg|thumb|Graph 3. Carbon positions.|590x590px|none]]

{| class="wikitable" border="1"
|+ typical bond length
! bond !! bond length(Å)
|-
| sp3-sp3 || 1.54
|-
| sp3–sp2 || 1.50
|-
| sp2–sp2 || 1.47
|-
| benzene || 1.40
|-
| alkene || 1.34
|}

As can see from '''graph 2''' , the bond length of the double bond in butadiene and ethylene decreases and the single bond in butadiene experiences a increase in bond length while two new bonds forms between two molecules.
The Van der Waals radius of the C atom is 1.70.
the partly form C-C has a bond length longer than normal sp3-sp3 single bond.

'''Illustrate the vibration that corresponds to the reaction path at the transition state. Is the formation of the two bonds synchronous or asynchronous?'''

Two bonds form synchronously.

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

'''Using your MO diagram for the Diels-Alder reaction, locate the occupied and unoccupied orbitals associated with the DA reaction for both TSs by symmetry. Find the relevant MOs and add them to your wiki (at an appropriate angle to show symmetry). Construct a new MO diagram using these new orbitals, adjusting energy levels as necessary. '''

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cyclohexdiene
|[[File:Cyclohexdiene_HOMO_as.png|250px]]
|[[File:Cyclohexdiene_LUMO_s.png|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|dioxole
|[[File:Dioxle_HOMO_s.png|250px]]
|[[File:Dioxole_LUMO_as.png|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of endo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:HOMO-1_as.jpg|344x344px]]
|[[image:HOMO_s.jpg|344x344px]]
|[[image:LUMO_s.jpg|344x344px]]
|[[image:LUMO+1_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the exo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_29_as.jpg|344x344px]]
|[[image:Level_30_s.jpg|344x344px]]
|[[image:Level_31_as.jpg|344x344px]]
|[[image:Level_32_s.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Anti-ymmetric (AS)
|Symmetric (S)
|}

It can been seen from the graph that endo product has the same orbital symmetry order (AS/S/S/AS from LUMO-1 to HOMO +1) with the the cyclohexene formation in exercise one, so it has a similar MO diagram with as graph**. However, the exo transition state has a different orbital symmetry order(AS /S/AS/S from LUMO-1 to HOMO). So the MO diagram is adjusted as following graph.

[[image:Exo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog exo reaction.]]
[[image:Endo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog endo reaction.]]

It is an inverse DA reactions. A normal DA reaction happen between a electron-poor dienophile and an electron rich diene. An inverse DA happen between an electron-rich dienophile and an electron-poor diene. In the case, the diene is not very electron poor nor electron rich, but dienophile 1,3-Dioxole is very electron rich due to direct attach to two electron donating oxygen atom. The orbital energy rises in dienophile and HOMO of dienolphile interact with LUMO of diene and form most energetically favored new orbital

'''In the .log files for each calculation, find a section named "Thermochemistry". Tabulate the energies and determine the reaction barriers and reaction energies (in kJ/mol) at room temperature (the corrected energies are labelled "Sum of electronic and thermal Free Energies", corresponding to the Gibbs free energy). Which are the kinetically and thermodynamically favourable products? '''

At room temperature,1 Hartree= 627.509 kcal mol-1

energy for Cyclohexadiene,0.118067. energy for 1,3-Dioxole -0.052286. Energy for reatant=(0.118067-0.052286)<math>\times</math>627.509kcal mol-1=41.27 kJ mol-1

energy for endo transition state, 0.137943<math>\times</math>627.509kcal mol-1=86.56 kJ mol-1
energy for endo product,0.037803<math>\times</math>627.509kcal mol-1=23.72 kJ mol-1

energy for exo transition state, 0.138903<math>\times</math>627.509kcal mol-1=87.16 kJ mol-1
energy for exo product,0.037975<math>\times</math>627.509kcal mol-1=23.83 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo
|45.89
|<math>-17.44</math>
|-
|endo
|45.29
|<math>-17.55</math>
|}

[[image:Exercise_2_reaction_coordinate.jpg|thumb|center|Graph **. reaction coordinate of endo and exo DA reaction.]]
The calculation shows that endo product are both kinetic and thermo product.

''ADD REFERENCE''

In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction. Thus, only the reaction between the HOMO of cyclopentadiene and the LUMO of maleic anhydride is allowed. Furthermore, though the exo-product is the more thermodynamically stable isomer, there are secondary (non-bonding) orbital interactions in the endo- transition state, lowering its energy and making the reaction towards the endo- product faster, and therefore more kinetically favorable. Since the exo-product has primary (bonding) orbital interactions it can still form, but since the endo-product forms faster it is the major product.

'''Look at the HOMO of the TSs. Are there any secondary orbital interactions or sterics that might affect the reaction barrier energy (Hint: in GaussView, set the isovalue to 0.01. In Jmol, change the mo cutoff to 0.01)? The Wikipedia page on Frontier Molecular Orbital Theory has some useful information on what these secondary orbital interactions are.'''

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

'''2) Visualise the reaction coordinate with an IRC calculation for each path. Include a .gif file in the wiki of these IRCs.'''

{| class="wikitable"
! colspan="3" |Table 4. reaction coordinate for three routes
|-
!cheletropic product
!exo
!endo
|-
|[[File:Exercise_3_cheletropic.gif|550px]]
|[[File:Exercise_3_endo.gif|550px]]
|[[File:Exercise_3_exo.gif|550px]]
|}

'''3) Calculate the activation and reaction energies (converting to kJ/mol) for each step as in Exercise 2 to determine which route is preferred.'''

At room temperature

The energy measurement in GaussView is in Hartree,
1 Hartree= 627.509 kcal mol-1

energy for so2, -0.118614.energy for xylyene,0.178554. Energy of the reactants=(-0.118614+0.178554)<math>\times</math>627.509kcal mol-1=37.61 kJ mol-1

energy for exo 6-membered-ring TS, 0.092079<math>\times</math>627.509kcal mol-1=57.78 kJ mol-1

energy for exo 6-membered-ring product, 0.056109<math>\times</math>627.509kcal mol-1=35.21 kJ mol-1

energy for endo 6-membered-ring TS, 0.090559<math>\times</math>627.509kcal mol-1=56.83 kJ mol-1

energy for endo 6-memberd-ring product, 0.021700<math>\times</math>627.509kcal mol-1=13 kJ mol-1

energy for 5-memberd-ring TS, 0.099060<math>\times</math>627.509kcal mol-1=62.16 kJ mol-1

energy for 5-memberd-ring product, -0.000002<math>\times</math>627.509kcal mol-1=-0.0012 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo 6-membered-ring
|20.17
|<math>-2.4</math>
|-
|endo 6-membered-ring
|19.22
|<math>-24.61</math>
|-
|5-memberd-ring
|24.55
|<math>-37.61</math>
|}

The endo Diels-Alder product is kinetically preferred as it has lowest activation energy.
The cheletropic product is aerodynamically preferred as it has lowest reaction energy.

'''4) Using Excel or Chemdraw, draw a reaction profile that contains relative heights of the energy levels of the reactants, TSs and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction. You can set the 0 energy level to the reactants at infinite separation.'''

[[image:New_MO_coordinate.jpg|thumb|center|reaction coordinate of three product.|344x344px]]
As can be seen in the graph. cheletropic product has the lowest energy so it is thermodynamic product. Endo product is the kinetic product.

'''Xylylene is highly unstable. Look at the IRCs for the reactions - what happens to the bonding of the 6-membered ring during the course of the reaction?'''

[[image:IRC_cheletropic_bond.png|530x530px]]
[[image:IRC_endo_bond.png|530x530px]]
[[image:IRC_exo_bond.png|530x530px]]

As can be seen from the graph, all nbond lengths changed. Two double bond on the ring extends and sing bonds shortens and finally all of they reaches a similar distances as the electron density delocalise in the 6 membered ring. The graph of endo and exo product are similar as they share the same structure. Cheletropic product has one bond slightly long than other. This is because the bond is shared with the neighboring 5 membered ring and experience a additional ring strain.

== Conclusion ==

Rep:Yc9014-transition

2017-03-24T10:20:48Z

Yc9014: /* Exercise 2:Reaction of Cyclohexadiene and 1,3-Dioxole */

== Introduction ==

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

HOMO and LUMO of both reactants can be visualized by GaussiView and shown in '''table 1''' as following.

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cis''-Butadiene
|[[File:Diene_HOMO_cyy.jpg|250px]]
|[[File:Diene_LUMO_cyy.jpg|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|Ethylene
|[[File:Ethene_HOMO_cyy.jpg|250px]]
|[[File:Ethene_LUMO_cyy.jpg|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

After the transition state was optimized and its identity proved by IRC, graph of the energy levels proceed from HOMO and LUMO of the reactants was visualized and shown in '''table 2'''.

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the reaction of butadiene and ethylene
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_16_as.jpg|344x344px]]
|[[image:Level_17_s.jpg|344x344px]]
|[[image:Level_18_s.jpg|344x344px]]
|[[image:Level_19_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

From the graphs in '''table 2'''

HOMO-1 is a in-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS),

HOMO is a in-phase combination of butadiene LUMO(S) and ethylene HOMO(S),

LUMO is a anti-phase combination of butadiene LUMO(S) and ethylene HOMOMO(S),

LUMO+1 is a anti-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS)

With these combination relationship and relative energy levels above, a MO diagram can be drawn as '''graph 1'''.

[[image:MO-1.jpg|thumb|center|Graph 1. MO diagram of transition state.]]

As indicated from the graph,the symmetry of two potential reacting orbitals must match with each other. ie. symmetric orbital interacts with symmetric orbital, asymmetric orbital interacts with asymmetric orbitals.
The orbital overlap can only be none-zero when the two orbitals have the same symmetry.For symmetrically mismatched orbitals(symmetric with asymmetric), no overlap means no interaction, therefore, no reaction happen.

{| class="wikitable" border="1"
|+ table 3
! symmetry interaction !! Orbital overlap integral
|-
| AS-AS || None-zero
|-
| AS-S || zero
|-
| S-S || none-zero
|}

'''bond length'''

[[image:Internuclear_distance_new.png|thumb|left|graph 2. Inter-nuclear distances of butadiene react with ethylene.|711x711px]]
[[image:Bond_distances_indicator.jpg|thumb|Graph 3. Carbon positions.|590x590px|none]]

{| class="wikitable" border="1"
|+ typical bond length
! bond !! bond length(Å)
|-
| sp3-sp3 || 1.54
|-
| sp3–sp2 || 1.50
|-
| sp2–sp2 || 1.47
|-
| benzene || 1.40
|-
| alkene || 1.34
|}

As can see from '''graph 2''' , the bond length of the double bond in butadiene and ethylene decreases and the single bond in butadiene experiences a increase in bond length while two new bonds forms between two molecules.
The Van der Waals radius of the C atom is 1.70.
the partly form C-C has a bond length longer than normal sp3-sp3 single bond.

'''Illustrate the vibration that corresponds to the reaction path at the transition state. Is the formation of the two bonds synchronous or asynchronous?'''

Two bonds form synchronously.

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

'''Using your MO diagram for the Diels-Alder reaction, locate the occupied and unoccupied orbitals associated with the DA reaction for both TSs by symmetry. Find the relevant MOs and add them to your wiki (at an appropriate angle to show symmetry). Construct a new MO diagram using these new orbitals, adjusting energy levels as necessary. '''

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cyclohexdiene
|[[File:Cyclohexdiene_HOMO_as.png|250px]]
|[[File:Cyclohexdiene_LUMO_s.png|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|dioxole
|[[File:Dioxle_HOMO_s.png|250px]]
|[[File:Dioxole_LUMO_as.png|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of endo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:HOMO-1_as.jpg|344x344px]]
|[[image:HOMO_s.jpg|344x344px]]
|[[image:LUMO_s.jpg|344x344px]]
|[[image:LUMO+1_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the exo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_29_as.jpg|344x344px]]
|[[image:Level_30_s.jpg|344x344px]]
|[[image:Level_31_as.jpg|344x344px]]
|[[image:Level_32_s.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Anti-ymmetric (AS)
|Symmetric (S)
|}

It can been seen from the graph that endo product has the same orbital symmetry order (AS/S/S/AS from LUMO-1 to HOMO +1) with the the cyclohexene formation in exercise one, so it has a similar MO diagram with as graph**. However, the exo transition state has a different orbital symmetry order(AS /S/AS/S from LUMO-1 to HOMO). So the MO diagram is adjusted as following graph.

[[image:Exo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog exo reaction.]]
[[image:Endo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog endo reaction.]]

It is an inverse DA reactions. A normal DA reaction happen between a electron-poor dienophile and an electron rich diene. An inverse DA happen between an electron-rich dienophile and an electron-poor diene. In the case, the diene is not very electron poor nor electron rich, but dienophile 1,3-Dioxole is very electron rich due to direct attach to two electron donating oxygen atom. The orbital energy rises in dienophile and HOMO of dienolphile interact with LUMO of diene and form most energetically favored new orbital

'''In the .log files for each calculation, find a section named "Thermochemistry". Tabulate the energies and determine the reaction barriers and reaction energies (in kJ/mol) at room temperature (the corrected energies are labelled "Sum of electronic and thermal Free Energies", corresponding to the Gibbs free energy). Which are the kinetically and thermodynamically favourable products? '''

At room temperature,1 Hartree= 627.509 kcal mol-1

energy for Cyclohexadiene,0.118067. energy for 1,3-Dioxole -0.052286. Energy for reatant=(0.118067-0.052286)<math>\times</math>627.509kcal mol-1=41.27 kJ mol-1

energy for endo transition state, 0.137943<math>\times</math>627.509kcal mol-1=86.56 kJ mol-1
energy for endo product,0.037803<math>\times</math>627.509kcal mol-1=23.72 kJ mol-1

energy for exo transition state, 0.138903<math>\times</math>627.509kcal mol-1=87.16 kJ mol-1
energy for exo product,0.037975<math>\times</math>627.509kcal mol-1=23.83 kJ mol-1

For B3LYP/6-31G(d) level calculation:energy for endo transition state, -500.332149,energy for exo transition state, -500.329164

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo
|45.89
|<math>-17.44</math>
|-
|endo
|45.29
|<math>-17.55</math>
|}

[[image:Exercise_2_reaction_coordinate.jpg|thumb|center|Graph **. reaction coordinate of endo and exo DA reaction.]]
The calculation shows that endo product are both kinetic and thermo product.

''ADD REFERENCE''

In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction. Thus, only the reaction between the HOMO of cyclopentadiene and the LUMO of maleic anhydride is allowed. Furthermore, though the exo-product is the more thermodynamically stable isomer, there are secondary (non-bonding) orbital interactions in the endo- transition state, lowering its energy and making the reaction towards the endo- product faster, and therefore more kinetically favorable. Since the exo-product has primary (bonding) orbital interactions it can still form, but since the endo-product forms faster it is the major product.

'''Look at the HOMO of the TSs. Are there any secondary orbital interactions or sterics that might affect the reaction barrier energy (Hint: in GaussView, set the isovalue to 0.01. In Jmol, change the mo cutoff to 0.01)? The Wikipedia page on Frontier Molecular Orbital Theory has some useful information on what these secondary orbital interactions are.'''

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

'''2) Visualise the reaction coordinate with an IRC calculation for each path. Include a .gif file in the wiki of these IRCs.'''

{| class="wikitable"
! colspan="3" |Table 4. reaction coordinate for three routes
|-
!cheletropic product
!exo
!endo
|-
|[[File:Exercise_3_cheletropic.gif|550px]]
|[[File:Exercise_3_endo.gif|550px]]
|[[File:Exercise_3_exo.gif|550px]]
|}

'''3) Calculate the activation and reaction energies (converting to kJ/mol) for each step as in Exercise 2 to determine which route is preferred.'''

At room temperature

The energy measurement in GaussView is in Hartree,
1 Hartree= 627.509 kcal mol-1

energy for so2, -0.118614.energy for xylyene,0.178554. Energy of the reactants=(-0.118614+0.178554)<math>\times</math>627.509kcal mol-1=37.61 kJ mol-1

energy for exo 6-membered-ring TS, 0.092079<math>\times</math>627.509kcal mol-1=57.78 kJ mol-1

energy for exo 6-membered-ring product, 0.056109<math>\times</math>627.509kcal mol-1=35.21 kJ mol-1

energy for endo 6-membered-ring TS, 0.090559<math>\times</math>627.509kcal mol-1=56.83 kJ mol-1

energy for endo 6-memberd-ring product, 0.021700<math>\times</math>627.509kcal mol-1=13 kJ mol-1

energy for 5-memberd-ring TS, 0.099060<math>\times</math>627.509kcal mol-1=62.16 kJ mol-1

energy for 5-memberd-ring product, -0.000002<math>\times</math>627.509kcal mol-1=-0.0012 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo 6-membered-ring
|20.17
|<math>-2.4</math>
|-
|endo 6-membered-ring
|19.22
|<math>-24.61</math>
|-
|5-memberd-ring
|24.55
|<math>-37.61</math>
|}

The endo Diels-Alder product is kinetically preferred as it has lowest activation energy.
The cheletropic product is aerodynamically preferred as it has lowest reaction energy.

'''4) Using Excel or Chemdraw, draw a reaction profile that contains relative heights of the energy levels of the reactants, TSs and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction. You can set the 0 energy level to the reactants at infinite separation.'''

[[image:New_MO_coordinate.jpg|thumb|center|reaction coordinate of three product.|344x344px]]
As can be seen in the graph. cheletropic product has the lowest energy so it is thermodynamic product. Endo product is the kinetic product.

'''Xylylene is highly unstable. Look at the IRCs for the reactions - what happens to the bonding of the 6-membered ring during the course of the reaction?'''

[[image:IRC_cheletropic_bond.png|530x530px]]
[[image:IRC_endo_bond.png|530x530px]]
[[image:IRC_exo_bond.png|530x530px]]

As can be seen from the graph, all nbond lengths changed. Two double bond on the ring extends and sing bonds shortens and finally all of they reaches a similar distances as the electron density delocalise in the 6 membered ring. The graph of endo and exo product are similar as they share the same structure. Cheletropic product has one bond slightly long than other. This is because the bond is shared with the neighboring 5 membered ring and experience a additional ring strain.

== Conclusion ==

Rep:Yc9014-transition

2017-03-24T10:15:47Z

Yc9014: /* Exercise 2:Reaction of Cyclohexadiene and 1,3-Dioxole */

== Introduction ==

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

HOMO and LUMO of both reactants can be visualized by GaussiView and shown in '''table 1''' as following.

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cis''-Butadiene
|[[File:Diene_HOMO_cyy.jpg|250px]]
|[[File:Diene_LUMO_cyy.jpg|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|Ethylene
|[[File:Ethene_HOMO_cyy.jpg|250px]]
|[[File:Ethene_LUMO_cyy.jpg|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

After the transition state was optimized and its identity proved by IRC, graph of the energy levels proceed from HOMO and LUMO of the reactants was visualized and shown in '''table 2'''.

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the reaction of butadiene and ethylene
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_16_as.jpg|344x344px]]
|[[image:Level_17_s.jpg|344x344px]]
|[[image:Level_18_s.jpg|344x344px]]
|[[image:Level_19_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

From the graphs in '''table 2'''

HOMO-1 is a in-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS),

HOMO is a in-phase combination of butadiene LUMO(S) and ethylene HOMO(S),

LUMO is a anti-phase combination of butadiene LUMO(S) and ethylene HOMOMO(S),

LUMO+1 is a anti-phase combination of butadiene HOMO(AS) and ethylene LUMO(AS)

With these combination relationship and relative energy levels above, a MO diagram can be drawn as '''graph 1'''.

[[image:MO-1.jpg|thumb|center|Graph 1. MO diagram of transition state.]]

As indicated from the graph,the symmetry of two potential reacting orbitals must match with each other. ie. symmetric orbital interacts with symmetric orbital, asymmetric orbital interacts with asymmetric orbitals.
The orbital overlap can only be none-zero when the two orbitals have the same symmetry.For symmetrically mismatched orbitals(symmetric with asymmetric), no overlap means no interaction, therefore, no reaction happen.

{| class="wikitable" border="1"
|+ table 3
! symmetry interaction !! Orbital overlap integral
|-
| AS-AS || None-zero
|-
| AS-S || zero
|-
| S-S || none-zero
|}

'''bond length'''

[[image:Internuclear_distance_new.png|thumb|left|graph 2. Inter-nuclear distances of butadiene react with ethylene.|711x711px]]
[[image:Bond_distances_indicator.jpg|thumb|Graph 3. Carbon positions.|590x590px|none]]

{| class="wikitable" border="1"
|+ typical bond length
! bond !! bond length(Å)
|-
| sp3-sp3 || 1.54
|-
| sp3–sp2 || 1.50
|-
| sp2–sp2 || 1.47
|-
| benzene || 1.40
|-
| alkene || 1.34
|}

As can see from '''graph 2''' , the bond length of the double bond in butadiene and ethylene decreases and the single bond in butadiene experiences a increase in bond length while two new bonds forms between two molecules.
The Van der Waals radius of the C atom is 1.70.
the partly form C-C has a bond length longer than normal sp3-sp3 single bond.

'''Illustrate the vibration that corresponds to the reaction path at the transition state. Is the formation of the two bonds synchronous or asynchronous?'''

Two bonds form synchronously.

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

'''Using your MO diagram for the Diels-Alder reaction, locate the occupied and unoccupied orbitals associated with the DA reaction for both TSs by symmetry. Find the relevant MOs and add them to your wiki (at an appropriate angle to show symmetry). Construct a new MO diagram using these new orbitals, adjusting energy levels as necessary. '''

{| class="wikitable"
! colspan="3" |Table1. HOMO and LUMO of reagents butadiene and ethene
|-
!
!HOMO
!LUMO
|-
|''cyclohexdiene
|[[File:Cyclohexdiene_HOMO_as.png|250px]]
|[[File:Cyclohexdiene_LUMO_s.png|250px]]
|-
|
|Anti-symmetric (AS)
|Symmetric (S)
|-
|dioxole
|[[File:Dioxle_HOMO_s.png|250px]]
|[[File:Dioxole_LUMO_as.png|250px]]
|-
|
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of endo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:HOMO-1_as.jpg|344x344px]]
|[[image:HOMO_s.jpg|344x344px]]
|[[image:LUMO_s.jpg|344x344px]]
|[[image:LUMO+1_as.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Symmetric (S)
|Anti-symmetric (AS)
|}

{| class="wikitable"
! colspan="4" |Table 2. energy levels for transition states of the exo DA reaction of Cyclohexadiene and 1,3-Dioxole
|-
!HOMO-1
!HOMO
!LUMO
!LUMO+1
|-
|[[image:Level_29_as.jpg|344x344px]]
|[[image:Level_30_s.jpg|344x344px]]
|[[image:Level_31_as.jpg|344x344px]]
|[[image:Level_32_s.jpg|344x344px]]
|-
|Anti-symmetric (AS)
|Symmetric (S)
|Anti-ymmetric (AS)
|Symmetric (S)
|}

It can been seen from the graph that endo product has the same orbital symmetry order (AS/S/S/AS from LUMO-1 to HOMO +1) with the the cyclohexene formation in exercise one, so it has a similar MO diagram with as graph**. However, the exo transition state has a different orbital symmetry order(AS /S/AS/S from LUMO-1 to HOMO). So the MO diagram is adjusted as following graph.

[[image:Exo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog exo reaction.]]
[[image:Endo_MO_diagram.jpg|thumb|center|Graph **. MO diagram of transition stateog endo reaction.]]

It is an inverse DA reactions. A normal DA reaction happen between a electron-poor dienophile and an electron rich diene. An inverse DA happen between an electron-rich dienophile and an electron-poor diene. In the case, the diene is not very electron poor nor electron rich, but dienophile 1,3-Dioxole is very electron rich due to direct attach to two electron donating oxygen atom. The orbital energy rises in dienophile and HOMO of dienolphile interact with LUMO of diene and form most energetically favored new orbital

'''In the .log files for each calculation, find a section named "Thermochemistry". Tabulate the energies and determine the reaction barriers and reaction energies (in kJ/mol) at room temperature (the corrected energies are labelled "Sum of electronic and thermal Free Energies", corresponding to the Gibbs free energy). Which are the kinetically and thermodynamically favourable products? '''

At room temperature,1 Hartree= 627.509 kcal mol-1

energy for Cyclohexadiene,0.118067. energy for 1,3-Dioxole -0.052286. Energy for reatant=(0.118067-0.052286)<math>\times</math>627.509kcal mol-1=41.27 kJ mol-1

energy for endo transition state, 0.137943<math>\times</math>627.509kcal mol-1=86.56 kJ mol-1
energy for endo product,0.037803<math>\times</math>627.509kcal mol-1=23.72 kJ mol-1

energy for exo transition state, 0.138903<math>\times</math>627.509kcal mol-1=87.16 kJ mol-1
energy for exo product,0.037975<math>\times</math>627.509kcal mol-1=23.83 kJ mol-1

For B3LYP/6-31G(d) level calculation:energy for endo transition state, -500.332149,energy for exo transition state, -500.329164

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo
|45.89
|<math>-17.44</math>
|-
|endo
|45.29
|<math>-17.55</math>
|}

[[image:Exercise_2_reaction_coordinate.jpg|thumb|center|Graph **. reaction coordinate of endo and exo DA reaction.]]
The calculation show that

''ADD REFERENCE''

In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction. Thus, only the reaction between the HOMO of cyclopentadiene and the LUMO of maleic anhydride is allowed. Furthermore, though the exo-product is the more thermodynamically stable isomer, there are secondary (non-bonding) orbital interactions in the endo- transition state, lowering its energy and making the reaction towards the endo- product faster, and therefore more kinetically favorable. Since the exo-product has primary (bonding) orbital interactions it can still form, but since the endo-product forms faster it is the major product.

'''Look at the HOMO of the TSs. Are there any secondary orbital interactions or sterics that might affect the reaction barrier energy (Hint: in GaussView, set the isovalue to 0.01. In Jmol, change the mo cutoff to 0.01)? The Wikipedia page on Frontier Molecular Orbital Theory has some useful information on what these secondary orbital interactions are.'''

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

'''2) Visualise the reaction coordinate with an IRC calculation for each path. Include a .gif file in the wiki of these IRCs.'''

{| class="wikitable"
! colspan="3" |Table 4. reaction coordinate for three routes
|-
!cheletropic product
!exo
!endo
|-
|[[File:Exercise_3_cheletropic.gif|550px]]
|[[File:Exercise_3_endo.gif|550px]]
|[[File:Exercise_3_exo.gif|550px]]
|}

'''3) Calculate the activation and reaction energies (converting to kJ/mol) for each step as in Exercise 2 to determine which route is preferred.'''

At room temperature

The energy measurement in GaussView is in Hartree,
1 Hartree= 627.509 kcal mol-1

energy for so2, -0.118614.energy for xylyene,0.178554. Energy of the reactants=(-0.118614+0.178554)<math>\times</math>627.509kcal mol-1=37.61 kJ mol-1

energy for exo 6-membered-ring TS, 0.092079<math>\times</math>627.509kcal mol-1=57.78 kJ mol-1

energy for exo 6-membered-ring product, 0.056109<math>\times</math>627.509kcal mol-1=35.21 kJ mol-1

energy for endo 6-membered-ring TS, 0.090559<math>\times</math>627.509kcal mol-1=56.83 kJ mol-1

energy for endo 6-memberd-ring product, 0.021700<math>\times</math>627.509kcal mol-1=13 kJ mol-1

energy for 5-memberd-ring TS, 0.099060<math>\times</math>627.509kcal mol-1=62.16 kJ mol-1

energy for 5-memberd-ring product, -0.000002<math>\times</math>627.509kcal mol-1=-0.0012 kJ mol-1

{|class="wikitable" border="1"
|+ activation energy and reaction energy for each route
|-
| || activation energy || reaction energy
|-
|exo 6-membered-ring
|20.17
|<math>-2.4</math>
|-
|endo 6-membered-ring
|19.22
|<math>-24.61</math>
|-
|5-memberd-ring
|24.55
|<math>-37.61</math>
|}

The endo Diels-Alder product is kinetically preferred as it has lowest activation energy.
The cheletropic product is aerodynamically preferred as it has lowest reaction energy.

'''4) Using Excel or Chemdraw, draw a reaction profile that contains relative heights of the energy levels of the reactants, TSs and products from the endo- and exo- Diels-Alder reactions and the cheletropic reaction. You can set the 0 energy level to the reactants at infinite separation.'''

[[image:New_MO_coordinate.jpg|thumb|center|reaction coordinate of three product.|344x344px]]
As can be seen in the graph. cheletropic product has the lowest energy so it is thermodynamic product. Endo product is the kinetic product.

'''Xylylene is highly unstable. Look at the IRCs for the reactions - what happens to the bonding of the 6-membered ring during the course of the reaction?'''

[[image:IRC_cheletropic_bond.png|530x530px]]
[[image:IRC_endo_bond.png|530x530px]]
[[image:IRC_exo_bond.png|530x530px]]

As can be seen from the graph, all nbond lengths changed. Two double bond on the ring extends and sing bonds shortens and finally all of they reaches a similar distances as the electron density delocalise in the 6 membered ring. The graph of endo and exo product are similar as they share the same structure. Cheletropic product has one bond slightly long than other. This is because the bond is shared with the neighboring 5 membered ring and experience a additional ring strain.

== Conclusion ==

File:Exercise 2 reaction coordinate.jpg

2017-03-24T10:13:31Z

Yc9014:

Rep:Yc9014-transition

File:LUMO+1 as.jpg

2017-03-24T08:51:33Z

Yc9014:

File:LUMO s.jpg

2017-03-24T08:51:16Z

Yc9014:

File:HOMO-1 as.jpg

2017-03-24T08:50:53Z

Yc9014:

File:HOMO s.jpg

2017-03-24T08:50:40Z

Yc9014: