Oxidative coupling of phenols. Part 8. A theoretical study of the coupling of phenoxyl radicals

Abstract

A theoretical study is described of the stereochemistry of mutual approach of two phenoxyl radicals. Both the CNDO and MINDO/3 methods are used and Morse curves are calculated for each reaction where the reaction co-ordinate is the interplanar distance. From a number of possible stereochemistries the most favoured involves an initial coaxial sandwich geometry, which undergoes conformational changes as bond formation between the two radical species occurs. The most energetically favoured path, which is given by the staggered form of the rings, leads to ortho-para- and ortho-ortho-coupled products. Of lesser importance is a head-to-tail approach which can lead to either ortho-ortho-carbon coupling or para-oxygen coupling. The para-para- and ortho-para-couplings obtained from the eclipsed form are of still smaller significance.