The electron spin resonance spectrum of the PPP-triphenylphosphomethylene radical-cation trapped in a crystalline matrix

Abstract

X-Irradiation of a single crystal of methyltriphenylphosphonium chloride results in the formation of the oriented radical-cation, Ph₃[graphic omitted]–ĊH₂. The electron spin resonance spectrum at room temperature shows that the methylene group is undergoing rapid reorientation over a two-fold energy barrier. At 100° K, however, this reorientation is too slow to affect the spectrum, which is here essentially that of the stationary radical. The anisotropic and isotropic components of the hyperfine coupling to the ¹H nuclei of the methylene group and of the ³¹P nucleus have been determined both at room temperature and at 100° K, and their values support a conclusion, reached from an earlier study of the radical-cation Ph₃[graphic omitted]–ĊHCO₂H, that there is little delocalisation of the unpaired electron on to the phosphorus atom.