Transition state geometry and a polar effect in the reactions of peroxy radicals with oxygen-containing compounds

The reactions of structurally different peroxy radicals with the C-H bonds of oxygen-containing compounds (ketones, aldehydes, ethers, and esters) were analyzed in terms of a parabolic model. The enthalpies of these reactions and the activation energies of equienthalpic reactions of peroxy radicals with hydrocarbons were calculated, and the contribution of the polar interaction DeltaE(mu), to the activation energy was evaluated. The geometry parameters of the transition state were calculated with the use of an algorithm developed based on quantum-chemical calculations in combination with the intersecting parabolas method. It was found that the polar interaction resulted in a change in the configuration of the C...H...O reaction center in the transition state from linear to angular. A different angle phi(C...H...O) from 180degrees appeared in this case. The following linear cor relation between DeltaE(mu) (kJ/mol) and cos (180degrees - phi) was obeyed: cos (180degrees - phi) = 1 + 6.76 x 10(-3) DeltaE(mu).