MINDO-FORCES Calculation of the Benzyl and Vinyl Radicals

The MIND0/3-F0RCES method is applied for the calculation of the 1CH2-1-H2 CH4 reaction. The variation of geometry is carried out in such a manner as to allow for the deviation from the Csv symmetry along the H7 —CH, 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 ß = 1.8Ä 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 AH[ value of 269.68 kcal/mol (274.0 kcal/mol exp.). The activation energy of the decomposition reaction CH4 + > CH3+ + His 84.54 kcal/mol, the reaction enthalpy is 42.83 kcal/mol (38.10 kcal/mol exp.). Using both MINDO/2and MIND0/3.F0RCES a Q>v geometry is calculated for the benzyl radical. The AHf 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 H{ value of 69.8 kcal/mol (65 kcal/mol exp.).