Electron spin resonance spectra of radical cations related to 1,3,5-trihydroxybenzene(phloroglucinol)

Abstract

Different e.s.r. parameters of radicals formed by the 1-electron oxidation of phloroglucinol (or of its O-methyl derivatives), vary differently with acid strength. This fact is consistent with there being at least two types of radical cation involved, a possibility which gains support from the observation of line broadening, which increases with acid strength. It is suggested that the line broadening is due to conformational changes of the methoxy groups in the neutral radicals, whereas the apparently anomalous variations of coupling constants arise from solvation effects, which might include changes in the relative concentrations of conformational isomers with acid strength. The magnitudes of the coupling constants are explained in terms of linear combinations of the symmetrical and antisymmetrical orbitals which are degenerate when trigonal symmetry is assumed.