A Variable Mechanism for the Nucleophilic Vinylic Substitutions in a Series of gem-Dihalogenated Alkenes by a Bidentate Sulfur Nucleophile: An Experimental and AM1 Theoretical Study

The nucleophilic substitutions of a series of gem-dihalogenated alkenes 3,5,7,8, and 9 (RS)₂C═CX₂ (X = Cl, F) with 1,2-benzenedithiolate b have been studied. Depending on the structures of the R groups (alkyl, saturated and unsaturated cycloalkyls, aromatic ring), the course of the reactions and the structures of the yielded products are modified. In the frame of the addition-elimination-type mechanism for these nucleophilic substitutions, the energy contents of the anionic intermediates, resulting from the additions of the nucleophile b to the unsaturated centers, is calculated at the AM1 method level. For the compounds 5, 7, 8, and 9, the calculated energies nicely corroborate the experimental results. For 3, anionic intermediates are no longer found by calculation, and a synchronous single-step substitution is strongly suggested.