Oxidative coupling of phenols. Part 9. The role of steric effects in the oxidation of methyl-substituted phenols

Abstract

MINDO/3 calculations indicate that for the coupling of 3,5-dimethylphenoxyl radicals the non-bonded methyl–methyl interactions cause the energy difference between the staggered (1b) and eclipsed (2b) geometries of approach to be greater than in the analogous coupling of phenoxyl radicals. The preferential and exclusive formation of the ortho-ortho-coupled products from the respective oxidations of 2,3-dimethylphenol and 2,3,5-trimethylphenol with di-t-butyl peroxide also support a mechanism, which proceeds viaa staggered transition state.