Polar radicals. VI. Bromination reactions with molecular bromine and N-bromosuccinimide. Apparent anomalies and similarities

Polar radicals. XI. Kinetic studies on the mechanism of the liquid phase bromination of 1-chlorobutane

“…The expression takes the form of [3] (a-position), [4] (P-position), and [5] (y-position), and each expression may in turn be integrated when the reaction is carried out to low conversion using high concentrations of bromine and hydrogen bromide.…”

“…By a combination of the integrated forms of [3], [5], and [I] or [4], [5], and [2], two expressions ( [6] and [7]) can be obtained that will allow an experimental evaluation of the effect of cage reversal on the ratio of products formed.…”

“…From the data in Table 1, using the integrated forms of 131, [4], and [5], and the vapor phase relative rate data for transfer of each radical with bromine and hydrogen bromide (see Table 2) the ratio of transfer rates with HBr, vs. HBr could be calculated for each position in the molecule. The value of [HBr,] could be obtained from the equilibrium constant, K = 2.8 + 0.3 (23"C), determined by the nmr method previously described (2).…”

“…lousing [6] We have previously suggested that the values obtained for the relative rates of bromination of several pairs of substrates in solvent liquid bromine (10-18 M) could be rationalized on the basis of competitive abstraction reactions which proceeded to products without internal (cage) or external return (5). In support of this suggestion that cage return can be interfered with by carrying out the brominations in very high concentrations of bromine it has been recently demonstrated that the deuterium isotope effect for the bromination of cyclohexane and perdeuteriocyclohexane, in the absence of external reversal, gave the same value, kR,/kR,, in the vapor phase and in solution (10-18 M liquid bromine) (3).…”

Recent controversy on imidyl radical chemistry

“…It is interesting to note that events leading to the recognition of the succinimidyl radical in 1972 emerged from the dispute over anchimeric assistance by neighboring bromine in bromine atom attack on the 8-hydrogen of alkyl bromide [21,[35][36][37][38], in which Traynham [36] had observed that the product patterns in the bromination of non-activated alkanic C-H bonds (e.g., l-bromobutane in Table I) are different with bromine and with NBS; therefore the succinimidyl radical must be partially sustaining the chain process in the latter as opposed to the purely bromine atom propagation in the former. The same group also demonstrated several reactivity differences and the presence of different bromine transfer processes in the two reagents toward unreactive alkanes, as shown below.…”