GENERATION AND DECAY OF ARYL SULFINYL AND SULFENYL RADICALS - A TRANSIENT ABSORPTION AND COMPUTATIONAL STUDY

Absorption spectra and extinction coefficients of phenylsulfinyl and p henylsulfenyl (thiyl) radicals are determined by nanosecond laser phot olysis in various solvents. Direct observation and characterization of arylsulfinyl radicals from the photolysis of several aromatic sulfoxi des provides the strongest evidence to date for a-cleavage as the pred ominant primary photochemical process for these compounds. The absorpt ion spectrum of phenylsulfinyl, with lambda(max) = 300 and 450 nm and epsilon = 1.1 x 10(4) and 1.3 x 10(3) M-1 cm(-1), is practically indep endent of solvent. Quantum yields of free sulfinyl radicals range from 0.09 to 0.18 in various solvents. Recombination rate constants very n ear diffusion control indicate that there is a large spin-orbital coup ling in the radical pair. Rate constants for the reactions of arylsulf inyl radicals with stable nitroxide radicals are among the fastest kno wn, but reactivity with O-2 is very modest. Computations indicate that the singly occupied molecular orbital is a pi orbital largely locali zed on the sulfur and oxygen atoms.