Steric effects observed in the electron spin resonance spectra of some arylsemiquinones

Abstract

The e.s.r. spectra of radicals derived from arylhydroquinones are discussed with particular reference to how the conformations of the radicals very with increasing ortho-substitution on the aryl group. With two ortho-substituents the dihedral angle becomes close to 90° so that the major splitting from the aryl group is from the meta-protons. The results are rationalised in terms of two contributions to the coupling constants of protons associated with the aryl group, one from the π electron system and the other from delocalisation through the σ bond framework.