Electron paramagnetic resonance studies of nitroxide radicals obtained from caryophyllene nitrosite

Abstract

Caryophyllene nitrosite is a versatile source of nitroxide radicals: eight different radicals have been derived from it. Two are obtained by allowing caryophyllene nitrosite in chloroform solution to react with iodine or with bromine; two by irradiating solid caryophyllene nitrosite with red light, or by irradiating solutions of caryophyllene nitrosite in toluene or in benzene with red light; two are obtained by irradiating solutions of caryophyllene nitrosite in ethanol with red light; one by irradiating solid caryophyllene nitrosite with u.v. radiation, and one by dissolving the last radical in chloroform. Three of these radicals have been isolated as pure, stable solids. Electron paramagnetic resonance spectra of the eight radicals are described and spin-Hamiltonian parameters, extracted from spectra of ‘glasses’ formed at 77°K by dispersing them in chloroform–toluene (3 : 2) solution, or from room-temperature spectra, are given. Structures for the nitroxide radicals, and some information about the mechanisms of the red and u.v. photolyses reactions, are deduced from the e.s.r. data.