α-Halogeno ketones have been dehalogenated with a combination of aluminium chloride and ethanethiol. The mechanism involved in deiodination and debromination differs from that of dechlorination and defluorination. A hard-hard interaction between carbonyl oxygen and aluminium chloride and a soft-soft interaction between iodine or bromine and thiol are the dominant factors for direct deiodination and debromination. In dechlorination and defluorination there is initial formation of the corresponding dithioacetal, whereby hard carbonyl oxygen is replaced by the soft sulphur atom. α-Chloro- and α-fluoro-dithioacetals then undergo dehalogenation to afford vinyl sulphide as a result both of a favourable soft-soft interaction between the sulphur atoms in the dithioacetal entity and thiol, and also a favourable hard-hard interaction between the nucleophilic chlorine or fluorine and aluminium chloride. α-Chloro- and α-fluoro-benzyl benzyl ketones afforded the dehalogenated product with concomitant 1,2-transposition of the carbonyl group. This suggests that there is an indirect path which operates competitively via a 1,2-dithio-olefin from α-halogenodithioacetals to vinyl sulphide. Addition of thiol to vinyl sulphide leads to the final product. A concept of hard-soft affinity inversion is proposed.