E.S.R. studies of some polycyclic semiquinones and derived radicals

Abstract

Oxidation of various 2,2?-dihydroxybiphenyls and binaphthyls gave ex. spectra which revealed no evidence of equal sharing of the unpaired electron between the two halves of the molecule. By contrast reduction of 3,3?- and 4,4?-di-t-butyl-2,5,2?,5?-diphenoquinones and of 2,2?-di- 1,4-naphthoquinone gave symmetrical spectra indicating rapid spin exchange between the rings. The species responsible are radical monoanions. Secondary radicals formed from naphthoquinones indicated the occurrence of hydroxylation. The formation of a substituted furan was also observed. The absence of splitting by one of the aromatic ring hydrogens in 2-hydroxy-1,4-naphthosemiquinones was noted and examination of a series of bromo-2-hydroxy-3-phenyl-1,4-naphthoquinones showed that splitting decreased in the order a_H(6) > a_H(8) > a_H(5) > a_H(7) with a_H(7), like a_H(3) in the semiquinones without a phenyl substituent at this position, usually being too small to be resolved.