The effect of fluorine as leaving group in the photolysis of 2-fluoro-1,2-diphenylethanone: Preparative and mechanistic investigation

Photolysis of 2-fluoro-1,2-diphenylethanone (1) in MeCN or MeOH produces mainly 2-phenylbenzofuran. In MeOH some traces of solvent addition to the benzoyl radical formed by α-cleavage were detected. In trifluoroethanol several products are due to direct α-cleavage. Only 3% of 2-phenylbenzofuran and 13% of the α-ketocation solvent adduct are formed. The triplet state of 1 observed in nanosecond experiment at low temperature has been confirmed in femtosecond experiment. The triplet is formed quite fast at 370 nm (rise time 4.5 ps in acetonitrile and 22 ps in trifluoroethanol) and is stable up to 1.9 ns (a lifetime of 20 ns has been determined by quenching experiments with naphthalene).