Multiple-photon chemistry in the benzophenone photoreduction during laser-jet photolysis: Effect of alcohol solvent on cross-coupling versus hydrogen abstraction of the electronically excited hydroxydiphenylmethyl radical

Article abstract of DOI:10.1016/0040-4020(96)00576-5

The ground state of the hydroxydiphenylmethyl radical (1) leads to benzpinacol (2) through head-to-head coupling and the diols 3 as cross-coupling product. In contrast, under the high-intensity conditions of the laser-jet photolysis, the excited radical 1* couples in the para position to afford the benzophenone derivatives 4 (head-to-tail coupling) (higher spin density at the para position/AM1 calculations). The major two-photon product is benzhydrol (5). The pronounced increase in hydrogen atom abstraction from MeOH to iPrOH by 1* is explained in terms of the greater electrophilic character of the electronically excited radical 1* versus its ground state.