Substituent effects in the e.s.r. spectra of phenoxyl radicals

Abstract

Regularities observed in the e.s.r. spectra of many o-, m- and p-substituted phenoxyl radicals allow unambiguous assignments of the coupling constants as well as the determination of their relative signs. It is shown that semiquinone anions can be classed as phenoxyl radicals and similarly for radicals from the oxidation of trihydroxybenzene derivatives.

With suitable parameters, the patterns of splittings in these radicals can be rationalised by means of McLachlan's SCF theory; a heteroatom model and an inductive model both explain most of the observed trends. INDO calculations gave a rather poor account of the splittings in phenoxyl.