Photolysis benzoin formation

Benzoins can also be synthesized by the photolysis of aldehydes at high concentration. The formation of benzoin can be rationalized as arising from intermolecular hydrogen abstraction followed by collapse of the radicals. 

The course of benzoin acetate photolysis in the presence of / - and y-CD in both solution and solid complexes is selective. Efficient caging for radical pair recombination induces a remarkable preference for the formation of a photocyclization product over type I products [283]. Similar cage effects improved selectivity for type II products in alkyldeoxybenzoin- -CD complexes in the solid state [284]. 

Homolysis can also be brought about by the action of radiation (usually ultraviolet), in which case it is termed photolysis. Examples are the dissociation of 2,2 -azobis(2-cyanopropane) and the formation of free radicals from benzophe-none (PhCOPh) and benzoin (PhCOCH(OH)Ph). An advantage of photolysis is that the formation of free radicals begins at the instant of exposure and ceases as soon as the light source is removed. 

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