The effect of electron attracting substituents on halogen addition to unsaturated compounds

Abstract

The addition of a halogen molecule to an unsaturated compound is a complex process in which many reactions may take place at the same time. The rate of addition is very sensitive to slight traces of impurities and different catalytic effects are possible, consequently it is quite understandable that the results of early workers are often complicated and difficult to interpret. However, in recent years by a more rigorous control of the experimental conditions it has been possible to isolate some of the main addition reactions and using these mechanisms as a working basis steady progress has been made in the understanding of the addition mechanisms. It was shown in 1925 by Francis (J.A.C.S. 1925, 47, 2340) that addition was a two stage process, and that in the bromination in aqueous solution a foreign ion could replace the bromine ion in the addition process. This led to the formulation of the reaction as