Two‐Photon Chemistry in the Laser Jet: Photochemistry of the Diphenylhydroxymethyl Radical

In the laser‐jet mode (argon ion laser) the excited hydroxy‐diphenylmethyl radical ( 3 * ) underwent H expulsion in inert solvents (benzene, acetonitrile) to produce benzophenone (two‐photon product), besides dimerization of its ground state 3 to benzpinacol (one‐photon product). In ethanol, the laser‐jet photolysis of benzophenone afforded as new products (two‐photon chemistry) benzhydrol, 4‐(1‐hydroxyethyl)benzophen‐one ( 1 ), together with benzpinacol and 1,1‐diphenyl‐1,2‐propandiol ( 4 ), which are also observed in low‐intensity photolyses (one‐photon chemistry). Benzhydrol is formed through H abstraction from the excited radical 3 * and ketone 1 possibly by coupling of an excited radical 3 * at its para position (highest spin density) with a transient 1‐hydroxyethyl radical. Photolysis of α‐phenylbenzoin ( 2 ) produced benzpinacol, benzophenone, pinacol 4 , benzhydrol, ketone 1 , and the benzoyl‐derived products benzil and benzaldehyde. Also benzhydrol was observed as a two‐photon product.