An ab initio quantum chemical study of reactions of hexano-6-lactam peroxy radicals with phenoxy or diphenyl radicals

Molecular mechanism of the inhibition reaction of lactam peroxy radicals with phenoxy and diphenylaminyl radicals yielding cyclic imide was studied. Ab initio quantum chemical methods-MP2 and DFT were used for models where benzene rings were replaced with methyl groups to find the transition state between the complex of starting radicals and the complex of products. Both methods give qualitatively similar results. For calculations of real systems with phenyl substituents, only DFT method was used. A transition state was round for the reaction of both types of radicals. The reaction can occur through a four-membered ring in the reaction center, breaking the O-O bond of the lactam peroxy radical HCOO. with simultaneous transfer of hydrogen from the carbon atom to the departing oxygen. The (OH)-O-. formed combines with the phenoxy or diphenylaminyl radical. The activation barriers for the suggested inhibition are very low (less than 30 kcal mol(-1)). Final gains of energy for the reaction were found to be about 70 kcal mol(-1) for diphenylaminyl radical and about 50 kcal mol(-1) for phenoxy radical. Thus, both reactions should be exothermic. (C) 2001 Elsevier Science Ltd. All rights reserved.