Reexamination of the Reaction of a "Graded Set" of Radicals with N-Bromosuccinimide: A Kinetic Argument Concerning the ? and ? States of Succinimidyl

Article abstract of DOI:10.1021/ja00309a026

The NBS brominations of methylene chloride with added substrates which yield stable radicals were reinvestigated.The proposal that these substrates would affect the ratio of β-bromopropionyl isocyanate (BPI)/bromodichloromethane, the solvent bromination product, was not substantiated.Bromination of 2,3-dimethylbutane, cyclohexene, and butadiene by NBS in CH2Cl2 plus vinylidene chloride gives essentially the same BPI/CHCl2Br ratios as in the presence of neopentane but large yields of brominated and polybrominated products.Similar reactions in the presence of up to 2.5 M benzene always yield BPI but also highly brominated benzene derivatives.BPI is detected in the NBS bromination of chloroform under all conditions and is the major product in the presence of vinylidene chloride.Photolysis of N-iodosuccinimide-I2 in CHCl3 gives β-iodopropionyl isocyanate as the chief product.None of these observations support the hypothesis of ? and ? states of the succinimidyl radical, while the NBS results appear consistent with competing S.-Br. chains.