2017-01-26T18:11:49Z

Ma8113:

Transition States

What is a transition state and a minimum?

A transition state is the highest energy structure that lies between the reactants and products.

Energy minimum is the minimum energy point along a reaction coordinate.

== '''1. Exercise 1''' ==

The 1,3 butadiene and ethylene were optimised at the PM6
level and the bond distance frozen at 2.2 angstroms using the redundant coordinate editor. Further calculations of optimization to a minimum were carried out to the output file. Optimization to a TS bermy and frequency analysis of the log file at the PM6 level, with the force constant being calculated once produced a transition state output file. Further analysis of the transition
state with the IRC method resulted in the output data as shown below in this section.

The IRC calculated results are shown below:
{| class="wikitable"
|[[File:MA8113 IRC ENERGY 16.jpg|thumb]]
|[[File:MA8113 IRC ENERGY 16A.jpg|thumb]]
|}

'''HOMO and LUMO Molecular Orbitals'''
{| class="wikitable"
!
!
=== LUMO ===
!
=== '''HOMO''' ===
|-
|
=== 1,3 Butadiene ===

=== (Diene) ===
|<gallery>
MA8113 ButadieneLUMO.jpg
</gallery>
|<gallery>
MA8113 ButadieneHOMO.jpg
</gallery>
|-
|
=== Ethylene ===

=== (Dienophile) ===
|<gallery>
MA8113 EtheneLUMO.jpg
</gallery>
|<gallery>
MA8113 EtheneHOMO.jpg
</gallery>
|-
|
=== Transition State ===
|<gallery>
MA8113 LUMO TS.jpg
</gallery>
|<gallery>
MA8113 HOMO TS.jpg
</gallery>
|}
For the Diels-Alder reaction to take place the diene must be in the cis conformation.The molecular orbital diagram of the Diels-Alder reaction with 1,3 butadiene and ethene is shown below. [[File:MA8113 MOexercise1.jpg|centre|thumb|Figure 1: Molecular orbital diagram of 1,3 butadiene and ethylene]]

This Diels-Alder reaction is thermally allowed in accordance with the Woodward-Hoffmann, see the analysis of the frontier orbitals below.
{| class="wikitable"
!
!
|-
![[File:MA8113 REACTANTS 1.jpg|thumb|329x329px|Figure 2: Reactants 1,3 butadiene and ethylene]]
![[File:MA8113 WOHOF.gif|thumb|Figure 3: Woodward–Hoffmann frontier orbitals]]
|}

The bonds lengths of the reactants:

The 4 C-C length of the 1,3 butadiene reactant is 4.2 angstrongs, see figure 2 (C1-C6).

The C-C length of ethylene is 1.4 angstrongs, see figure 2 (C11-C12)

The bond lengths of the transition state:

The 6 C-C length of the transition state is 5.6 angstrongs.

The C-C bond lengths of the product is 8.96 angstrongs

The van der Waals radius of a carbon atom is 1.70 angstrongs this is larger than 1.42 angstrongs
of a partially formed C-C bond.<ref>S.S. Batsanov, ''Inorg. Mater.'', 2001, '''37''' (9), 871-885.</ref>

=== Orbital overlap: ===
Symmetric- Asymmetric would give a zero integral

Symmetric- Symmetric would give a non-zero integral

Asymmetric- Asymmetric would give a zero integral

== Exercise 2: ==
'''Endo product'''
[[File:MA8113 Endo2.jpg|centre|thumb|Figure 4]]The reactants were optimized at a minimum PM6 level and the transition state was obtained using frequency and optimization method at a PM6 level. Analysis of the vibration result showed a value of -960.04 cm-1.

The HOMO and LUMO of the endo transition state is shown below:<gallery>

</gallery>

{| class="wikitable"
|[[File:MA8113 LUMO TS.jpg|thumb|178x178px|LUMO]]
|[[File:MA8113 HOMO TS.jpg|thumb|178x178px|HOMO]]
|}

'''Reaction coordinate Diagram:'''
{| class="wikitable"
![[File:MA8113 ENDO ENERGY.jpg|thumb|Figure 5]]
!The activation energy of the reaction is 131 kJ/mol

and the reaction energy is 75 kJ/mol.

|}

This reaction is a normal electron demand Diels-Alder reaction.

The endo product is the thermodynamic product.
The IRC for this reaction ig given below:
[[File:MA8113 IRC ENDO.jpg|thumb|centre|Figure 6]]

'''Exo Product'''

[[File:MA8113 EXO 123.jpg|centre|thumb|Figure 7]]

Optimizing the reaction at PM6 level and at a set distance of 2.2 angstrong and further optimization and frequency calculation using the PM6 level method, with the bonds frozen obtain a transition state with a negative frequency of -958.64. The HOMO and LUMO of the Exo product are given below.

{| class="wikitable"
![[File:MA8113 HOMO 1 EXO.jpg|thumb|178x178px]]
![[File:MA8113 LUMO 1 EXO.jpg|thumb|178x178px]]
|}

'''Reaction coordinate energy diagram'''

IRC analysis with force constant always and following in both direction at PM6 level obtain results as shown below.
[[File:MA8113 EXO IRC.jpg|left|thumb|Figure 8]]
{| class="wikitable"
![[File:MA8113 EXO ENERGY.jpg|thumb|Figure 9]]
!Reaction coordinate:

The activation energy is 140 kJ/mol and the reaction energy is 144 kJ/mol.
|}

The exo product is the kinetic product. The reaction is an inverse demand Diels-Alder reaction.

'''''<nowiki/>'''''

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

==== 1. Diels-Alder ====
{| class="wikitable"
![[File:MA8113 Structure ENDO (TS).jpg|thumb|The transition state]]
![[File:MA8113 Structure ENDO.jpg|thumb|The adduct]]
|}

The IRC calculation using the PM6 method with calculation of the force constant once in both directions the result is outlined below:
{| class="wikitable"
![[File:MA8113 IRC CAL 1.jpg|thumb]]
![[File:MA8113 IRC CAL 2.jpg|thumb]]
|}
The activation energy of this reaction 25 kJ/mol and the overall change in energy is 172 kJ/mol

The reaction coordinate is given below:
[[File:EXO ENERGYDIAGRAM-101.jpg|thumb|centre]]

2. Cheletropic

{| class="wikitable"
![[File:MA8113 ts C2.jpg|thumb|Adduct]]
![[File:MA8113 ADDUCT C1.jpg|thumb|Transition state]]
!
|}

Rep:Mod:MA8113

2017-01-26T17:34:47Z

Ma8113: /* Exercise 3: Diels-Alder vs Cheletropic reaaction */

Transition States

What is a transition state and a minimum?

A transition state is the highest energy structure that lies between the reactants and products.

Energy minimum is the minimum energy point along a reaction coordinate.

== '''1. Exercise 1''' ==

The 1,3 butadiene and ethylene were optimised at the PM6
level and the bond distance frozen at 2.2 angstroms using the redundant coordinate editor. Further calculations of optimization to a minimum were carried out to the output file. Optimization to a TS bermy and frequency analysis of the log file at the PM6 level, with the force constant being calculated once produced a transition state output file. Further analysis of the transition
state with the IRC method resulted in the output data as shown below in this section.

The IRC calculated results are shown below:
{| class="wikitable"
|[[File:MA8113 IRC ENERGY 16.jpg|thumb]]
|[[File:MA8113 IRC ENERGY 16A.jpg|thumb]]
|}

'''HOMO and LUMO Molecular Orbitals'''
{| class="wikitable"
!
!
=== LUMO ===
!
=== '''HOMO''' ===
|-
|
=== 1,3 Butadiene ===

=== (Diene) ===
|<gallery>
MA8113 ButadieneLUMO.jpg
</gallery>
|<gallery>
MA8113 ButadieneHOMO.jpg
</gallery>
|-
|
=== Ethylene ===

=== (Dienophile) ===
|<gallery>
MA8113 EtheneLUMO.jpg
</gallery>
|<gallery>
MA8113 EtheneHOMO.jpg
</gallery>
|-
|
=== Transition State ===
|<gallery>
MA8113 LUMO TS.jpg
</gallery>
|<gallery>
MA8113 HOMO TS.jpg
</gallery>
|}
For the Diels-Alder reaction to take place the diene must be in the cis conformation.The molecular orbital diagram of the Diels-Alder reaction with 1,3 butadiene and ethene is shown below. [[File:MA8113 MOexercise1.jpg|centre|thumb|Figure 1: Molecular orbital diagram of 1,3 butadiene and ethylene]]

This Diels-Alder reaction is thermally allowed in accordance with the Woodward-Hoffmann, see the analysis of the frontier orbitals below.
{| class="wikitable"
!
!
|-
![[File:MA8113 REACTANTS 1.jpg|thumb|329x329px|Figure 2: Reactants 1,3 butadiene and ethylene]]
![[File:MA8113 WOHOF.gif|thumb|Figure 3: Woodward–Hoffmann frontier orbitals]]
|}

The bonds lengths of the reactants:

The 4 C-C length of the 1,3 butadiene reactant is 4.2 angstrongs, see figure 2 (C1-C6).

The C-C length of ethylene is 1.4 angstrongs, see figure 2 (C11-C12)

The bond lengths of the transition state:

The 6 C-C length of the transition state is 5.6 angstrongs.

The C-C bond lengths of the product is 8.96 angstrongs

The van der Waals radius of a carbon atom is 1.70 angstrongs this is larger than 1.42 angstrongs
of a partially formed C-C bond.<ref>S.S. Batsanov, ''Inorg. Mater.'', 2001, '''37''' (9), 871-885.</ref>

=== Orbital overlap: ===
Symmetric- Asymmetric would give a zero integral

Symmetric- Symmetric would give a non-zero integral

Asymmetric- Asymmetric would give a zero integral

== Exercise 2: ==
'''Endo product'''
[[File:MA8113 Endo2.jpg|centre|thumb|Figure 4]]The reactants were optimized at a minimum PM6 level and the transition state was obtained using frequency and optimization method at a PM6 level. Analysis of the vibration result showed a value of -960.04 cm-1.

The HOMO and LUMO of the endo transition state is shown below:<gallery>

</gallery>

{| class="wikitable"
|[[File:MA8113 LUMO TS.jpg|thumb|178x178px|LUMO]]
|[[File:MA8113 HOMO TS.jpg|thumb|178x178px|HOMO]]
|}

'''Reaction coordinate Diagram:'''
{| class="wikitable"
![[File:MA8113 ENDO ENERGY.jpg|thumb|Figure 5]]
!The activation energy of the reaction is 131 kJ/mol

and the reaction energy is 75 kJ/mol.

|}

This reaction is a normal electron demand Diels-Alder reaction.

The endo product is the thermodynamic product.
The IRC for this reaction ig given below:
[[File:MA8113 IRC ENDO.jpg|thumb|centre|Figure 6]]

'''Exo Product'''

[[File:MA8113 EXO 123.jpg|centre|thumb|Figure 7]]

Optimizing the reaction at PM6 level and at a set distance of 2.2 angstrong and further optimization and frequency calculation using the PM6 level method, with the bonds frozen obtain a transition state with a negative frequency of -958.64. The HOMO and LUMO of the Exo product are given below.

{| class="wikitable"
![[File:MA8113 HOMO 1 EXO.jpg|thumb|178x178px]]
![[File:MA8113 LUMO 1 EXO.jpg|thumb|178x178px]]
|}

'''Reaction coordinate energy diagram'''

IRC analysis with force constant always and following in both direction at PM6 level obtain results as shown below.
[[File:MA8113 EXO IRC.jpg|left|thumb|Figure 8]]
{| class="wikitable"
![[File:MA8113 EXO ENERGY.jpg|thumb|Figure 9]]
!Reaction coordinate:

The activation energy is 140 kJ/mol and the reaction energy is 144 kJ/mol.
|}

The exo product is the kinetic product. The reaction is an inverse demand Diels-Alder reaction.

'''''<nowiki/>'''''

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

==== 1. Diels-Alder ====
{| class="wikitable"
![[File:MA8113 Structure ENDO (TS).jpg|thumb|The transition state]]
![[File:MA8113 Structure ENDO.jpg|thumb|The adduct]]
|}

The IRC calculation using the PM6 method with calculation of the force constant once in both directions the result is outlined below:
{| class="wikitable"
![[File:MA8113 IRC CAL 1.jpg|thumb]]
![[File:MA8113 IRC CAL 2.jpg|thumb]]
|}
The activation energy of this reaction 25 kJ/mol and the overall change in energy is 172 kJ/mol

The reaction coordinate is given below:
[[File:EXO ENERGYDIAGRAM-101.jpg|left|thumb]]

2. Cheletropic

{| class="wikitable"
![[File:MA8113 ts C2.jpg|thumb|Adduct]]
![[File:MA8113 ADDUCT C1.jpg|thumb|Transition state]]
!
|}

2017-01-26T16:55:38Z

Ma8113:

Rep:Mod:MA8113

2017-01-26T16:52:57Z

Ma8113: /* Orbital overlap: */

Transition States

What is a transition state and a minimum?

A transition state is the highest energy structure that lies between the reactants and products.

Energy minimum is the minimum energy point along a reaction coordinate.

== '''1. Exercise 1''' ==

The 1,3 butadiene and ethylene were optimised at the PM6
level and the bond distance frozen at 2.2 angstroms using the redundant coordinate editor. Further calculations of optimization to a minimum were carried out to the output file. Optimization to a TS bermy and frequency analysis of the log file at the PM6 level, with the force constant being calculated once produced a transition state output file. Further analysis of the transition
state with the IRC method resulted in the output data as shown below in this section.

The IRC calculated results are shown below:
{| class="wikitable"
|[[File:MA8113 IRC ENERGY 16.jpg|thumb]]
|[[File:MA8113 IRC ENERGY 16A.jpg|thumb]]
|}

'''HOMO and LUMO Molecular Orbitals'''
{| class="wikitable"
!
!
=== LUMO ===
!
=== '''HOMO''' ===
|-
|
=== 1,3 Butadiene ===

=== (Diene) ===
|<gallery>
MA8113 ButadieneLUMO.jpg
</gallery>
|<gallery>
MA8113 ButadieneHOMO.jpg
</gallery>
|-
|
=== Ethylene ===

=== (Dienophile) ===
|<gallery>
MA8113 EtheneLUMO.jpg
</gallery>
|<gallery>
MA8113 EtheneHOMO.jpg
</gallery>
|-
|
=== Transition State ===
|<gallery>
MA8113 LUMO TS.jpg
</gallery>
|<gallery>
MA8113 HOMO TS.jpg
</gallery>
|}
For the Diels-Alder reaction to take place the diene must be in the cis conformation.The molecular orbital diagram of the Diels-Alder reaction with 1,3 butadiene and ethene is shown below.[[File:MA8113 MOexercise1.jpg|centre|thumb|Figure 1: Molecular orbital diagram of 1,3 butadiene and ethylene]]

This Diels-Alder reaction is thermally allowed in accordance with the Woodward-Hoffmann, see the analysis of the frontier orbitals below.
{| class="wikitable"
!
!
|-
![[File:MA8113 REACTANTS 1.jpg|thumb|329x329px|Figure 2: Reactants 1,3 butadiene and ethylene]]
![[File:MA8113 WOHOF.gif|thumb|Figure 3: Woodward–Hoffmann frontier orbitals]]
|}

The bonds lengths of the reactants:

The 4 C-C length of the 1,3 butadiene reactant is 4.2 angstrongs, see figure 2 (C1-C6).

The C-C length of ethylene is 1.4 angstrongs, see figure 2 (C11-C12)

The bond lengths of the transition state:

The 6 C-C length of the transition state is 5.6 angstrongs.

The C-C bond lengths of the product is 8.96 angstrongs

The van der Waals radius of a carbon atom is 1.70 angstrongs this is larger than 1.42 angstrongs
of a partially formed C-C bond.<ref>S.S. Batsanov, ''Inorg. Mater.'', 2001, '''37''' (9), 871-885.</ref>

=== Orbital overlap: ===
Symmetric- Asymmetric would give a zero integral

Symmetric- Symmetric would give a non-zero integral

Asymmetric- Asymmetric would give a zero integral

== Exercise 2: ==
'''Endo product'''
[[File:MA8113 Endo2.jpg|centre|thumb]]The reactants were optimized at a minimum PM6 level and the transition state was obtained using frequency and optimization method at a PM6 level. Analysis of the vibration result showed a value of -960.04.

The HOMO and LUMO of the endo transition state is shown below:<gallery>

</gallery>

{| class="wikitable"
|[[File:MA8113 LUMO TS.jpg|thumb|178x178px|LUMO]]
|[[File:MA8113 HOMO TS.jpg|thumb|178x178px|HOMO]]
|}
<nowiki>*</nowiki>** '''Molecular orbital diagram:'''

'''Reaction coordinate Diagram:'''
{| class="wikitable"
![[File:MA8113 ENDO ENERGY.jpg|thumb]]
!The activation energy of the reaction is 131 kJ/mol

and the reaction energy is 75 kJ/mol.

|}

This reaction is a normal electron demand Diels-Alder reaction.

The endo product is the thermodynamic product.
[[File:MA8113 IRC ENDO.jpg|thumb|centre]]

'''Exo Product'''

[[File:MA8113 EXO 123.jpg|centre|thumb]]

Optimizing the reaction at PM6 level and at a set distance of 2.2 angstrong and further optimization and frequency calculation using the PM6 level method, with the bonds frozen obtain a transition state with a negative frequency of -958.64.

The HOMO and LUMO molecular orbitals are given below:

IRC analysis with force constant always and following in both direction at PM6 level obtain results as shown below.

'''Reaction coordinate:'''
[[File:MA8113 EXO IRC.jpg|left|thumb]]

{| class="wikitable"
![[File:MA8113 EXO ENERGY.jpg|thumb]]
!The activation energy is 140 kJ/mol and the reaction energy is 144 kJ/mol.
|}

The exo product is the kinetic product. The reaction is an inverse demand Diels-Alder reaction.

The reaction energy coordinate diagram for the exo product is given below:[[File:MA8113 HOMO 1 EXO.jpg|left|thumb|150x150px|HOMO of the Exo Product]]

[[File:MA8113 LUMO 1 EXO.jpg|left|thumb|150x150px|LUMO of Exo Product]]

'''''<nowiki/>'''''

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

==== 1. Diels-Alder ====
{| class="wikitable"
![[File:MA8113 Structure ENDO (TS).jpg|thumb|The transition state]]
![[File:MA8113 Structure ENDO.jpg|thumb|The adduct]]
|}

The IRC calculation using the PM6 method with calculation of the force constant once in both directions the result is outlined below:
{| class="wikitable"
![[File:MA8113 IRC CAL 1.jpg|thumb]]
![[File:MA8113 IRC CAL 2.jpg|thumb]]
|}
The activation energy of this reaction 25 kJ/mol and the overall change in energy is 172 kJ/mol

2. Cheletropic

{| class="wikitable"
![[File:MA8113 ts C2.jpg|thumb|Adduct]]
![[File:MA8113 ADDUCT C1.jpg|thumb|Transition state]]
!
|}

Ma8113: Ma8113 uploaded a new version of File:MA8113 EXO 123.jpg

File:MA8113 EXO 123.jpg

2017-01-26T16:21:54Z

Ma8113:

Rep:Mod:MA8113

2017-01-26T16:19:22Z

Ma8113: /* Transition State */

Transition States

What is a transition state and a minimum?

A transition state is the highest energy structure that lies between the reactants and products.

Energy minimum is the minimum energy point along a reaction coordinate.

== '''1. Exercise 1''' ==

The 1,3 butadiene and ethylene were optimised at the PM6
level and the bond distance frozen at 2.2 angstroms using the redundant coordinate editor. Further calculations of optimization to a minimum were carried out to the output file. Optimization to a TS bermy and frequency analysis of the log file at the PM6 level, with the force constant being calculated once produced a transition state output file. Further analysis of the transition
state with the IRC method resulted in the output data as shown below in this section.

The IRC calculated results are shown below:
{| class="wikitable"
|[[File:MA8113 IRC ENERGY 16.jpg|thumb]]
|[[File:MA8113 IRC ENERGY 16A.jpg|thumb]]
|}

'''HOMO and LUMO Molecular Orbitals'''
{| class="wikitable"
!
!
=== LUMO ===
!
=== '''HOMO''' ===
|-
|
=== 1,3 Butadiene ===

=== (Diene) ===
|<gallery>
MA8113 ButadieneLUMO.jpg
</gallery>
|<gallery>
MA8113 ButadieneHOMO.jpg
</gallery>
|-
|
=== Ethylene ===

=== (Dienophile) ===
|<gallery>
MA8113 EtheneLUMO.jpg
</gallery>
|<gallery>
MA8113 EtheneHOMO.jpg
</gallery>
|-
|
=== Transition State ===
|<gallery>
MA8113 LUMO TS.jpg
</gallery>
|<gallery>
MA8113 HOMO TS.jpg
</gallery>
|}
For the Diels-Alder reaction to take place the diene must be in the cis conformation.The molecular orbital diagram of the Diels-Alder reaction with 1,3 butadiene and ethene is shown below.[[File:MA8113 MOexercise1.jpg|centre|thumb|Figure 1: Molecular orbital diagram of 1,3 butadiene and ethylene]]

This Diels-Alder reaction is thermally allowed in accordance with the Woodward-Hoffmann, see the analysis of the frontier orbitals below.
{| class="wikitable"
!
!
|-
![[File:MA8113 REACTANTS 1.jpg|thumb|329x329px|Figure 2: Reactants 1,3 butadiene and ethylene]]
![[File:MA8113 WOHOF.gif|thumb|Figure 3: Woodward–Hoffmann frontier orbitals]]
|}

The bonds lengths of the reactants:

The 4 C-C length of the 1,3 butadiene reactant is 4.2 angstrongs, see figure 2 (C1-C6).

The C-C length of ethylene is 1.4 angstrongs, see figure 2 (C11-C12)

The bond lengths of the transition state:

The 6 C-C length of the transition state is 5.6 angstrongs.

The C-C bond lengths of the product is 8.96 angstrongs

The van der Waals radius of a carbon atom is 1.70 angstrongs this is larger than 1.42 angstrongs
of a partially formed C-C bond.<ref>S.S. Batsanov, ''Inorg. Mater.'', 2001, '''37''' (9), 871-885.</ref>

=== Orbital overlap: ===
Symmetric- Asymmetric would give a zero integral

Symmetric- Symmetric would give a non-zero integral

Asymmetric- Asymmetric would give a zero integral

== Exercise 2: ==
'''Endo product'''
[[File:MA8113 Endo2.jpg|centre|thumb]]The reactants were optimized at a minimum PM6 level and the transition state was obtained using frequency and optimization method at a PM6 level. Analysis of the vibration result showed a value of -960.04.

The HOMO and LUMO of the endo transition state is shown below:<gallery>

</gallery>

<nowiki> </nowiki><nowiki>*</nowiki>** '''Molecular orbital diagram:'''
{| class="wikitable"
|[[File:MA8113 LUMO TS.jpg|thumb|178x178px|LUMO]]
|[[File:MA8113 HOMO TS.jpg|thumb|178x178px]]
|}

Thermochemistry: -0.0561797 Hartrees which is -147 kJ/mol

This reaction is a normal electron demand Diels-Alder reaction.

The endo product is the thermodynamic product.
[[File:MA8113 IRC ENDO.jpg|thumb|centre]]

'''Exo Product'''

Optimizing the reaction at PM6 level and at a set distance of 2.2 angstrong and further optimization and frequency calculation using the PM6 level method, with the bonds frozen obtain a transition state with a negative frequency of -958.64.

IRC analysis with force constant always and following in both direction at PM6 level obtain results as shown below.

The exo product is the kinetic product. The reaction is an inverse demand Diels-Alder reaction.
[[File:MA8113 HOMO 1 EXO.jpg|left|thumb|150x150px|HOMO of the Exo Product]]

[[File:MA8113 LUMO 1 EXO.jpg|left|thumb|150x150px|LUMO of Exo Product]]

'''''<nowiki/>'''''

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

==== 1. Diels-Alder ====
{| class="wikitable"
![[File:MA8113 Structure ENDO (TS).jpg|thumb|The transition state]]
![[File:MA8113 Structure ENDO.jpg|thumb|The adduct]]
|}

The IRC calculation using the PM6 method with calculation of the force constant once in both directions the result is outlined below:
{| class="wikitable"
![[File:MA8113 IRC CAL 1.jpg|thumb]]
![[File:MA8113 IRC CAL 2.jpg|thumb]]
|}
The activation energy of this reaction 25 kJ/mol and the overall change in energy is 172 kJ/mol

2. Cheletropic

{| class="wikitable"
![[File:MA8113 ts C2.jpg|thumb|Adduct]]
![[File:MA8113 ADDUCT C1.jpg|thumb|Transition state]]
!
|}

Rep:Mod:MA8113

2017-01-26T16:18:23Z

Ma8113: 1

Transition States

What is a transition state and a minimum?

A transition state is the highest energy structure that lies between the reactants and products.

Energy minimum is the minimum energy point along a reaction coordinate.

== '''1. Exercise 1''' ==

The 1,3 butadiene and ethylene were optimised at the PM6
level and the bond distance frozen at 2.2 angstroms using the redundant coordinate editor. Further calculations of optimization to a minimum were carried out to the output file. Optimization to a TS bermy and frequency analysis of the log file at the PM6 level, with the force constant being calculated once produced a transition state output file. Further analysis of the transition
state with the IRC method resulted in the output data as shown below in this section.

The IRC calculated results are shown below:
{| class="wikitable"
|[[File:MA8113 IRC ENERGY 16.jpg|thumb]]
|[[File:MA8113 IRC ENERGY 16A.jpg|thumb]]
|}

'''HOMO and LUMO Molecular Orbitals'''
{| class="wikitable"
!
!
=== LUMO ===
!
=== '''HOMO''' ===
|-
|
=== 1,3 Butadiene ===

=== (Diene) ===
|<gallery>
MA8113 ButadieneLUMO.jpg
</gallery>
|<gallery>
MA8113 ButadieneHOMO.jpg
</gallery>
|-
|
=== Ethylene ===

=== (Dienophile) ===
|<gallery>
MA8113 EtheneLUMO.jpg
</gallery>
|<gallery>
MA8113 EtheneHOMO.jpg
</gallery>
|-
|
=== Transition State ===
|<gallery>
MA8113 LUMO TS.jpg
</gallery>
|<gallery>
MA8113 HOMO TS.jpg
</gallery>
|}
For the Diels-Alder reaction to take place the diene must be in the cis conformation.The molecular orbital diagram of the Diels-Alder reaction with 1,3 butadiene and ethene is shown below.[[File:MA8113 MOexercise1.jpg|centre|thumb|Figure 1: Molecular orbital diagram of 1,3 butadiene and ethylene]]

This Diels-Alder reaction is thermally allowed in accordance with the Woodward-Hoffmann, see the analysis of the frontier orbitals below.
{| class="wikitable"
!
!
|-
![[File:MA8113 REACTANTS 1.jpg|thumb|329x329px|Figure 2: Reactants 1,3 butadiene and ethylene]]
![[File:MA8113 WOHOF.gif|thumb|Figure 3: Woodward–Hoffmann frontier orbitals]]
|}

The bonds lengths of the reactants:

The 4 C-C length of the 1,3 butadiene reactant is 4.2 angstrongs, see figure 2 (C1-C6).

The C-C length of ethylene is 1.4 angstrongs, see figure 2 (C11-C12)

The bond lengths of the transition state:

The 6 C-C length of the transition state is 5.6 angstrongs.

The C-C bond lengths of the product is 8.96 angstrongs

The van der Waals radius of a carbon atom is 1.70 angstrongs this is larger than 1.42 angstrongs
of a partially formed C-C bond.<ref>S.S. Batsanov, ''Inorg. Mater.'', 2001, '''37''' (9), 871-885.</ref>

=== Orbital overlap: ===
Symmetric- Asymmetric would give a zero integral

Symmetric- Symmetric would give a non-zero integral

Asymmetric- Asymmetric would give a zero integral

== Exercise 2: ==
'''Endo product'''
[[File:MA8113 Endo2.jpg|centre|thumb]]The reactants were optimized at a minimum PM6 level and the transition state was obtained using frequency and optimization method at a PM6 level. Analysis of the vibration result showed a value of -960.04.

The HOMO and LUMO of the endo transition state is shown below:<gallery>

</gallery>

<nowiki> </nowiki><nowiki>*</nowiki>** '''Molecular orbital diagram:'''
{| class="wikitable"
|[[File:MA8113 LUMO TS.jpg|thumb|178x178px|LUMO]]
|
|}

Thermochemistry: -0.0561797 Hartrees which is -147 kJ/mol

This reaction is a normal electron demand Diels-Alder reaction.

The endo product is the thermodynamic product.
[[File:MA8113 IRC ENDO.jpg|thumb|centre]]

'''Exo Product'''

Optimizing the reaction at PM6 level and at a set distance of 2.2 angstrong and further optimization and frequency calculation using the PM6 level method, with the bonds frozen obtain a transition state with a negative frequency of -958.64.

IRC analysis with force constant always and following in both direction at PM6 level obtain results as shown below.

The exo product is the kinetic product. The reaction is an inverse demand Diels-Alder reaction.
[[File:MA8113 HOMO 1 EXO.jpg|left|thumb|150x150px|HOMO of the Exo Product]]

[[File:MA8113 LUMO 1 EXO.jpg|left|thumb|150x150px|LUMO of Exo Product]]

'''''<nowiki/>'''''

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

==== 1. Diels-Alder ====
{| class="wikitable"
![[File:MA8113 Structure ENDO (TS).jpg|thumb|The transition state]]
![[File:MA8113 Structure ENDO.jpg|thumb|The adduct]]
|}

The IRC calculation using the PM6 method with calculation of the force constant once in both directions the result is outlined below:
{| class="wikitable"
![[File:MA8113 IRC CAL 1.jpg|thumb]]
![[File:MA8113 IRC CAL 2.jpg|thumb]]
|}
The activation energy of this reaction 25 kJ/mol and the overall change in energy is 172 kJ/mol

2. Cheletropic

{| class="wikitable"
![[File:MA8113 ts C2.jpg|thumb|Adduct]]
![[File:MA8113 ADDUCT C1.jpg|thumb|Transition state]]
!
|}