Chemistry Department, Kuwait University, Kuwait Manuscript received 22 October 1973; revised 29 March 1975; accepted 29 April 1975 The reactions between bromine and chloroprene (2-chloro-1,3-butadiene), bromine and iso­prene (2-methyl-1,3-butadiene) and chlorine and isoprene have been investigated. The reaction between bromine and chloroprene goes essentially by 1, 4-addition to give trans-2-chloro-1, 4-dibromo-2-butene with a small amount of 1, 2-and 3, 4-addition as indicated by lithium aluminum hydride reduction of the reaction products. Similar analysis of the reaction products from bromine and isoprene is complicated by allylic rearrangement of the 1, 2-and 3, 4-addition products to the 1, 4-addition product and also by the fact that the lithium aluminum hydride reduction of both of these addition products could give 2-methyl-2-butene, the reduction product of the 1, 4-addition compound. The products of the reduction consist only of those arising from the 1, 2-, 3, 4-and 1, 4-addition compounds. No. monobromo diene was obtained. The reaction between chlorine and isoprene yields a rnonochloride, 2-chloromethyl-1, 3 -butadiene, and both 3, 4-dichloro -2 -methyl -1 -1 -butene and 1, 4 -dichloro - 2 methyl-2-butene. These compounds are formed by 3, 4-and 1, 4-additions respectively. The mechanistic implications of these reactions are discussed.