The intramolecular hydrogen atom transfer in the photodissociation of o-chlorotoluene

Based on ab initio calculated results, a new mechanism is proposed that intramolecular hydrogen atom transfer may occur during the photodissociation of o-chlorotoluene at 266 nm. This mechanism is different from the general suggestion, i.e. (1) o-chlorotoluene (S-1) --> o-chlorotoluene (T-1) --> Cl + o-tolyl --> benzyl + Cl. Our suggestion is (2) o-chlorotoluene(S-1) --> o-chlorotoluene (T-1,S-0) --> 5-methylene-6-chloro-1,3-cyclohexadiene(MCC) (S-0) --> benzyl + Cl. Our results show that the energy barrier of the rearrangement from o-tolyl to benzyl in path (1) is too high to be overcome, but the intramolecular H atom transfer of o-chlorotoluene in path (2) may be more reasonable. (C) 1998 Elsevier Science B.V