Competition Between C?-S and C?-C? Bond Cleavage in ?-Hydroxysulfoxides Cation Radicals Generated by Photoinduced Electron Transfer+

A kinetic and product study of the 3-cyano-N-methyl-quinolinium photoinduced monoelectronic oxidation of a series of ?-hydroxysulfoxides has been carried out to investigate the competition between C?-S and C?-C? bond cleavage within the corresponding cation radicals. Laser flash photolysis experiments unequivocally established the formation of sulfoxide cation radicals showing their absorption band (?max ? 520?nm) and that of 3-CN-NMQo (?max ? 390?nm). Steady-state photolysis experiments suggest that, in contrast to what previously observed for alkyl phenyl sulfoxide cation radicals that exclusively undergo C?-S bond cleavage, the presence of a ?-hydroxy group makes, in some cases, the C?-C? scission competitive. The factors governing this competition seem to depend on the relative stability of the fragments formed from the two bond scissions. Substitution of the ?-OH group with -OMe did not dramatically change the reactivity pattern of the cation radicals thus suggesting that the observed favorable effect of the hydroxy group on the C?-C? bond cleavage mainly resides on its capability to stabilize the carbocation formed upon this scission. ? 2021 The Authors. Photochemistry and Photobiology published by Wiley Periodicals LLC on behalf of American Society for Photobiology.