On the Mechanism of N-Bromosuccinimide Brominations. Bromination of Cyclohexane and Cyclopentane with N-Bromosuccinimide

Article abstract of DOI:10.1021/jo00164a021

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 solvents 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 the other of the chain processes.No evidence was obtained, from studies of the NBS halogenation of the two substrates used, which required the intermediacy of an excited-state succinimidyl radical to explain the reactivities obtained.The observation that β-bromopropionyl isocyanate is produced under all of the reaction conditions precludes the requirement that brominations using the NBS-Br2 reagent proceed exclusively by a radical species whose reactions do not correlate with a ring-opening process.