Transition State Modeling - Computer Modeling Studies I Ground State Modeling

C. Computer Modeling Studies I Ground State Modeling

II. Transition State Modeling

A transition state calculation was carried out on each ester in both the S-cis and S-trans conformation, except in the cases of angelic methyl ester and methyl 3,3-dimethyl acrylate which do not have significant concentrations of the S-trans isomer at room temperature. Two transition state models were carried out for each ester conformer relating to the two faces of attack of dimethyldioxirane described as “in” and “out”, where “in” describes the methyl groups of the dioxirane positioned over the carbonyl group, or in the plane of the molecule, and “out” describes the 180 degree flip of that. Methyl esters were used in all cases to simplify the calculations, and minimize errors that may be derived from rotation of an ethoxy group, and comparison of the energy of a methyl group vs. that of an ethyl group. Each transition state energy was used along with the ground state calculations and a ground state energy calculation of dimethyldioxirane to find the energy of activation of the reaction. Calculations were first undertaken using a semi empirical approach using the AM-1 method where the heat of formation of the starting materials, transition state, and dimethyldioxirane were used to calculate the energy of activation at 23O C. (Tables 21-27).

Table 21: Ground state, transition state, and activation energies for the reaction of methyl acrylate with dimethyldioxirane using the AM-1 method.

Methyl acrylate (6) Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea in

(Kcal/mol) Ea out (Kcal/mol)

S-cis -69.616 -40.04 -39.479 18.868 19.429

S-trans -70.037 -39.477 -39.292 19.852 20.037

Table 22: Ground state, transition state, and activation energies for the reaction of methyl crotonate with dimethyldioxirane using the AM-1 method.

Methyl crotonate (5) Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea In

(Kcal/mol) Ea Out (Kcal/mol)

S-cis -80.574 -49.406 -48.897 20.46 20.969

S-trans -80.138 -48.82 -48.728 20.61 20.702

Table 23: Ground state, transition state, and activation energies for the reaction of methyl 3,3- dimethyl acrylate with dimethyldioxirane using the AM-1 method.

Methyl 3,3 dimethyl acrylate (4) Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea In

(Kcal/mol) Ea Out (Kcal/mol)

Table 24: Ground state, transition state, and activation energies for the reaction of methyl methacrylate with dimethyldioxirane using the AM-1 method.

Methyl methacrylate (2)

Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea In

(Kcal/mol) Ea Out (Kcal/mol) S-trans -76.530 -45.959 -45.397 19.863 20.425

S-cis -76.642 -46.303 -45.309 19.631 20.625

Table 25: Ground state, transition state, and activation energies for the reaction of angelic methyl ester with dimethyldioxirane using the AM-1 method.

Angelic methyl ester (3)

Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea In

(Kcal/mol) Ea Out (Kcal/mol) S-cis -85.48 -52.667 -52.514 22.105 22.258

Table 26: Ground state, transition state, and activation energies for the reaction of tiglic methyl ester with dimethyldioxirane using the AM-1 method.

Tiglic methyl

ester (1) Ground state energy (Kcal/mol) Transition state energy In. (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea in

(Kcal/mol) Ea out (Kcal/mol) S-cis -85.819 -53.757 -52.35 21.354 22.761 S-trans -85.596 -52.751 -52.795 22.137 22.093

Table 27: Ground state, transition state, and activation energies for the reaction of 1-methyl cyclohexene carboxylate with dimethyldioxirane using the AM-1 method.

Methyl- 1 - cyclohexene-1- carboxylate (8)

Ground state energy (Kcal/mol) Transition state energy In. (Kcal/mol) Transition state energy Out. (Kcal/mol) Ea In

(Kcal/mol) Ea Out (Kcal/mol) S-trans -93.945 -59.775 -61.037 23.726 22.2

Table 28: Ground state, transition state, and activation energies for the reaction of 1-methyl cyclopentene carboxylate with dimethyldioxirane using the AM-1 method.

Methyl -1- cyclopentene-1- carboxylate (9)

Ground state energy (Kcal/mol) Transition state energy In (Kcal/mol) Transition state energy out (K/cal/mol) Ea In

(Kcal/mol) Ea out (Kcal/mol) S-cis -81.091 -47.19 -48.283 23.193 22.100 S-trans -81.059 -48.068 -46.923 22.283 23.428

The transition state calculations were also carried out using the density functional level with a 6-31 G* basis set to compare to the semi-empirical calculations (Tables 29-36).

Table 29: Ground state, transition state, and activation energies for the reaction of methyl acrylate with dimethyldioxirane using the density functional method.

Methyl acrylate (7)