Primary processes in the type I photocleavage of dibenzyl ketones. A pulsed laser and photochemically induced dynamic nuclear polarization study

The primary homolytic α-cleavage, and subsequent decarbonylation of the intermediate phenacyl radicals, have been studied for the type I photoreaction of a series of dibenzyl ketones, using the techniques of pulsed laser photolysis and photochemically induced dynamic nuclear polarization (photo-CIDNP). Evidence for selective primary cleavage to produce the most stable radical pairs is obtained for unsymmetrical ketones. The absolute rate constants and activation parameters for the decarbonylations are obtained, and the relationship between these and the stabilities of the product radicals is discussed.