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

The ground state of the hydroxydiphenylmethyl radical (1) leads to ben zpinacol (2) through head-to-head coupling and the diols 3 as cross-co upling product. In contrast. under the high-intensity conditions of th e laser-jet photolysis. the excited radical 1 couples in the para pos ition to afford the benzophenone derivatives 4 (head-to-tail coupling) (higher spin density at the para position / AM1 calculations). The ma jor two-photon product is benzhydrol (5). The pronounced increase in h ydrogen atom abstraction from MeOH to iPrOH by 1 is explained in term s of the greater electrophilic character of the electronically excited radical 1 versus its ground state. Copyright (C) 1996 Elsevier Scien ce Ltd