The addition of chlorine and bromine to ethyl sorbate (la) gave 1, 2-and 1, a-dihalo products derived from attack of the halogen across the y, 6 double bond. Chlorination of la under ionic conditions proceeds through a tightly bridged chloronium ion intermediate, as indicated by the stereospecific formation of erythro-1, 2-dichloride 3a. Stereospecificity in 3a is lost when chlorine is added to la under radical conditions, indicating a molecule-induced homolysis ...
