ESR spectra of free radicals derived from N-aryl- and N-sulphonylaryl-1,4-benzoquinone imines

Article abstract of DOI:10.1016/0022-2860(91)80121-J

ESR spectra of free radicals from 23 derivatives of 1,4-benzoquinone imines, obtained by electrochemical or chemical reduction of these compounds or by oxidation of the corresponding p-aminophenols, have been studied in solution.In the course of the processes mentioned, anion radicals of 1,4-benzoquinone imines are formed while in the case of reduction of N-sulphonyl derivatives (depending on the potential of electrochemical generation) neutral radicals can be obtained as well.Anion radicals of the corresponding 1,4-benzoquinones are formed in the case of N-arylbenzoquinone imines; they can also be obtained in other cases if the water content in the solution is high enough (apparently as a result of hydrolysis).The pathways of free radical formation and their structural peculiarities are discussed.Neutral free radicals of 1,4-benzoquinone sulphonyldiimines are stable enough to be isolated in the solid phase.The latter are assumed to be of quinoid structure with protonated imine nitrogen.