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

Molecular mechanism of the inhibition reaction of lactam peroxy radicals wi th phenoxy and diphenylaminyl radicals yielding cyclic imide was studied. A b initio quantum chemical methods-MP2 and DFT were used for models where be nzene rings were replaced with methyl groups to find the transition state b etween the complex of starting radicals and the complex of products. Both m ethods 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 t hrough a four-membered ring in the reaction center, breaking the O-O bond o f the lactam peroxy radical HCOO. with simultaneous transfer of hydrogen fr om the carbon atom to the departing oxygen. The (OH)-O-. formed combines wi th the phenoxy or diphenylaminyl radical. The activation barriers for the s uggested inhibition are very low (less than 30 kcal mol(-1)). Final gains o f energy for the reaction were found to be about 70 kcal mol(-1) for diphen ylaminyl radical and about 50 kcal mol(-1) for phenoxy radical. Thus, both reactions should be exothermic. (C) 2001 Elsevier Science Ltd. All rights r eserved.