MINDO-FORCES Calculation of the Benzyl and Vinyl Radicals and the Reactions 1CH2 + H2 → CH4 and CH4 .+ → CH3 + + H

Abstract

Abstract The MINDO/3-F0RCES method is applied for the calculation of the 1CH2+H2 → CH4 reaction. The variation of geometry is carried out in such a manner as to allow for the deviation from the C2v symmetry along the H7 -CH2 reaction coordinate. The changes in the geometric parameters of the system during the reaction are followed. It is found that the transition state of the reaction corresponds to R = 1.8 Å and has a geometry closer to the reactants than the products. The calculated activation energy is 13.57 kcal/mol and the calculated reaction enthalpy 106.36 kcal/mol (118.9 kcal/mol exp.). Similar calculations for the CH4 .+ yield a D2d structure and a ⊿Hf value of 269.68 kcal/mol (274.0 kcal/mol exp.). The activation energy of the decomposition reaction CH4 .+ → CH3 + + H· is 84.54 kcal/mol, the reaction enthalpy is 42.83 kcal/mol (38.10 kcal/mol exp.). Using both MINDO/2- and MINDO/3.FORCES a C2v geometry is calculated for the benzyl radical. The ⊿Hf values are 48.40 and 67.93 kcal/mol respectively. The latter calculation shows that the rotated perpendicular conformation of the methylene group is by 2 kcal/mol less stable than the planar one. The rotation transition state corresponds to the rotation angle 50°. The change in ithe geometric parameters during the rotation is followed. For he vinyl radical the MINDO/3-FORCES calculation yields a CCH angle of 151.1° and a Hf value of 69.8 kcal/mol (65 kcal/mol exp.).