The oxidation potentials ofcis- andtrans-1,2-diphenylcyclopropane (1) andcis- andtrans-2,3-diphenyloxirane (2) have been determined by cyclic voltammetry, spectroscopically (using an empirical correlation of the long wavelength transition of the charge-transfer complexes with tetracyanoethylene) and by using an empirical correlation based upon the gas phase ionization potentials measured by photoelectron spectroscopy. The values obtained by these three very different techniques agree to within ±0.15 V. The results are interpreted in terms of the initial formation of the phenyl radical cation with the three-membered ring intact. The higher oxidation potentials ofcis- andtrans-2, relative to those ofcis- andtrans-1, are attributed to inductive electron withdrawal from the phenyl group by the oxygen of the oxirane ring. The relevance of these results to the photosensitized (electron transfer) behaviour of these compounds is discussed.