Multiple bond migration with participation of a protophilic agent 4. Double bond migration in 3-methylthioprop-1-ene and 3-methoxyprop-1-ene: a comparative study

Ab initio study of the pathways of migration of the double bond in the 3-methylthioprop-1-ene (1) and 3-methoxyprop-1-ene (2) molecules with participation of hydroxide ion was carried out by the RHF/6-31+G* and MP2/6-31+G//RHF/6-31+G* methods, Conformational isomerism of the initial molecules and reaction products was considered. The distinctions are discussed in the spatial and electronic structure of intermediate carbanions stabilized (for 1) due to the negative hyperconjugation. Stationary points corresponding to complexes between the molecules under study and the hydroxide ion and between the corresponding carbanion and water molecule were localized on the potential energy surfaces of the proton transfer reactions. For 2, the single-stage mechanism of prototropic rearrangement involving the H atom of the hydroxide ion was found to be more energetically preferable than the two-stage mechanism, whereas both mechanisms are expected to be equiprobable for 1.