Kinetic effects in the electron spin resonance spectra of some semiquinones

Abstract

Protonation of semiquinones gives rise to kinetic effects in their e.s.r. spectra; these have been analysed by making use of changes in relative line heights with acid concentration. Supported by data which indicate that radical ions cannot be present in significant concentrations over the relevant range of acidities, it is shown that in each case studied, only the neutral species need be considered in the interpretation of the kinetic effects. Rate constants for the proton exchanges are calculated and coupling constants for the fully protonated forms (positive ions) are given for the semiquinones from hydroquinone, catechol, resorcinol and from phloroglucinol.