Participation by neighbouring groups in addition reactions. Part II. Effect of neighbouring bromine in the bromination and iodination of olefins

Abstract

Rate measurements have been carried out for the bromination (in methanol) and iodination (in water) of the bromo-olefins CH₂CH[CH₂]_nBr for n= 1–4. The bromination results were analysed by use of an attenuation plot which showed clearly that there was no rate enhancement over that expected on polar grounds. No attenuation plot was done for the iodinations since no rate data are available for the unsubstituted compounds but inspection of the second-order rate coefficients shows a rate maximum for n= 3 which suggests a degree of anchimeric assistance by the neighbouring bromine atom in this case. The magnitude of the effect is markedly less than for the reaction of the corresponding alcohols (–OH participation), i.e., OH(5) Br(5) and Br(6) is not detected.