The electron spin resonance spectra of semiquinones obtained from some naturally occurring methoxybenzoquinones

Abstract

Radical anions of methoxyquinones and related compounds were generated in a static system in alkaline media. The unpaired electron distribution in these radicals could not be satisfactorily verified by simplified SCF calculations. It is shown that a simple relationship exists between splittings in the semiquinones and corresponding splittings in the closely related alkyl aryl ether radical cations. This relationship correlates very closely with the excess charge effect which has been examined quantitatively for aromatic hydrocarbon radical ions, indicating that the same effect is operative in the oxygenated radicals, in which the splittings of the cations are ca. 20% greater than corresponding splittings in the anions. These correlations, together with observed smooth variations of splitting patterns with substitution have permitted unambiguous assignment of the coupling constants of radicals such as the fumigatin anion or the 1,2-methylenedioxynaphthalene cation, without recourse to new computation.