Photochemical bromination of arenes. 2. Fluorobenzene derivatives[1]

Photochemically induced reaction of fluorobenzene and a range of polyfluorobenzenes, both in an excess of the arene and with fluorotrichloromethane as solvent, gave isolable adducts only with fluorobenzene, the isomeric difluorobenzenes, and in very small yield with 1,3,5-tri-fluorobenzene. These adducts were identified by combustion analysis, mass spectrometry, and n.m.r. techniques ( 1 H, 19 C, 19 F). In every case, the expected substitution products accompanied these adducts, and in the more fully fluorinated benzene derivatives substitution was the only process observed. Fluorotrichloromethane encouraged the formation of adducts, but the concurrent formation of substantial amounts of substitution products suggested that adducts are not the necessary precursors of the substitution products, in contrast with other systems.