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The vapor-phase photobromination of 1-bromobutane with molecular bromine (5:1) yields 11 products resulting from direct substitution or the elimination of a bromine atom from the 1 -(bromomethyl)propyl radical. The 1 -butene resulting from elimination undergoes addition, and allylic substitution and addition to yield polyhalogenated materials. The major portion of the bromine (65% ) produced 1,2,3-tribromobutane and 1,2,3,4-tetrabromobutane. Bromination with bromine-81 produced isotopically enriched products which were consistent with the proposed mechanism and showed that 33% of the 1,2-dibromobutane formed arose from the elimination-readdition process. Vapor phase photobromination carried out to partial completion with high concentrations of bromine and hydrogen bromide resulted in only minimal amounts of 0 scission of the 1 -(bromomethyl)propyl radicals. Under these conditions the bromination of perdeuterio-1-bromobutane allowed the determination of the relative rates of transfer, with bromine and hydrogen bromide, of the radicals formed in the reaction and further allowed the determination of the relative rates of abstraction at each position in the molecule. The relative rates of transfer and abstraction indicate that the radical formed 0 to the electronegative bromine atom is stabilized (i.e., more easily formed and less reactive with hydrogen bromide) compared to those in the other positions in the molecule.

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The competitive N-bromosuccinimide (NBS) bromination of cyclopentane vs. cyclohexane was shown to proceed by a mechanism dominated by either a bromine atom chain, a succinimidyl chain, or a mixed chain. The dominance of each of the major chain-carrying processes depends upon the solventa used, to some degree upon the reactivity of the substrate, and upon the additives (molecular bromine or ethylene) used to moderate or enhance one or (8) Tanner, D. D.; Mcaher, M. W.; Das, N. C.; Blackburn, E. V. J. Am. (9) Traynham, J. G.; Green, E. E.; Lee, Y. S.; Schweinsberg, F.; Low, (IO) Tanner, D. D.; Ruo, T. C.-S.; Takiguchi. H.: Guillaume. A. Can. Chem. SOC. 1971,93,5846. C . E. J. Am. Chem. SOC. 1972,94,6552. J . Chem. 1981,59, 1368.

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