Abstract An electron spin resonance study on a series of phenylphosphoranyl radicals generated either by uv irradiation of solutions containing the corresponding P (III) or P (V) compounds and a dialkylperoxide, or by electrochemical reduction of the phosphonium salts, is reported. It is demonstrated, by careful examination of the phenylphosphoranyl radicals formed, that the initial precursor structure strongly defines the ultimate structure of ...