Photochemistry of polyhaloarenes. 9. Characterization of the radical anion intermediate in the photodehalogenation of polyhalobenzenes

The product-determining intermediate in the photodehalogenation of polyhalobenzenes has been characterized by generating excimers and radical anions within a micellar core and by formation of corresponding radical anions by electron transfer from lithium p,p'-di-tert-butylbiphenyl radical anion (LiDBB). The photodechlorination of pentachlorobenzene (1; 254 nm, CH 3 CN) produces 1,2,3,5-tetrachloro- (2), 1,2,4,5-tetrachloro- (3), and 1,2,3,4-tetrachlorobenzene (4). The regiochemistry of this reaction is compared with that observed in the photodechlorination of 1 in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) with occupancy numbers (n) principally <2 and 2. Further comparisons with photodechlorination of 1 in a micellar CTAB solution (n<2) in the presence of triethylamine, as well as photodechlorination in CH 3 CN in the presence of triethylamine, were used to characterize unencumbered radical anions