Halogen addition to unsaturated hydrocarbons

Abstract

The classical picture of halogen addition to olefins postulated a simultaneous addition of both atoms in the halogen molecule. This view was disproved by McKenzie (Proc. Chem. Soc. 1911, 150) and Frankland (J.C.S. 1912, 673) who showed that trans addition occurred in these reactions. For example, maleic acid gave racemic dibromo succinic acid with bromine, not the meso acid. Norrish (J.C.S. 1923, 3006) found that the reaction ethylene + bromine in the gas phase takes place on a polar surface only, indicating ionic intermediates.