Photochemistry of Polyhaloarenes. 6. The Fragmentation of Polyfluoroarene Radical Anions

Article abstract of DOI:10.1021/jo00378a016

The quantum yields for photolyses of pentafluorobenzene in the presence of different concentrations of triethylamine in acetonitrile and pentane were determined at 254 nm.Excimer formation was probed through a study of the quantum yield dependence for pentafluorobenzene photolysis upon substrate concentration in the absence of triethylamine.The linear dependence of 1/Φ vs. 1/(ArF) is complemented by an analysis of product composition, which revealed the production in a 30-min photolysis of the following: 1.2.3.5-tetrafluorobenzene (2) (0.11percent), 1,2,4,5-tetrafluorobenzene (3) (1.09percent), 1,2,3,4-tetrafluorobenzene (4) (0.09percent), octafluorobiphenyl (four isomers, 0.26, 0.85, 0.91, and 0.8percent), and HF (3.01percent).The regiochemistry of the monodefluorination of pentafluorobenzene, 1,2,3,5-tetrafluorobenzene, and 1,2,3,4-tetrafluorobenzene in the presence of triethylamine in acetonitrile or pentane (cyclohexane) was determined and is rationalized in terms of fission of the parent radical anion through a bent transition state.