The addition of chlorine, bromine chloride and bromine to methyl 2-chloropropenoate 1, methyl cis - 3 - chloropropenoate 2 and methyl trans - 3 - chloropropenoate 3 under ionic and radical conditions gave regioisomer mixtures. Both trans- and cis-addition of halogen species was observed, bromine preferentially adding to the non-halogenated carbon atom.