Electron spin resonance studies. Part XI. Heterolytic fragmentations of hydroxycyclohexadienyl radicals

Abstract

Several monosubstituted benzenoid compounds are oxidised by the system, titanous ion–hydrogen peroxide, to give, according to the pH, either cyclohexadienyl radicals (by addition of the hydroxyl radical to the aromatic ring) or radicals formed by the loss of a group from the side-chain; this group may be H, CO₂H, or CH₂·OH. It is argued that the former radicals are formed first and that, if they have the appropriate structural features, they undergo acid-catalysed heterolytic bond ruptures in which hydroxide ion is eliminated from the ring and a proton, or a proton and carbon dioxide or formaldehyde, is lost from the side-chain.