Transition state geometry and polar effect in the addition of peroxyl radicals to olefins

Transition-state interatomic distances in the addition of peroxyl radicals to the double bond of olefins are estimated from experimental data (activation energies and rate constants) using a new algorithm combining quantum chemical and parabolic model calculations. An aromatic ring in the alpha-position with respect to the double bond elonoates the C center dot center dot center dot O distance by 0.02 x 10(-10) in. Polar groups aqjacent to the double bond affect this distance considerably. The geometric parameters of the transition states in the abstraction and addition of peroxyl radicals are compared.