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-me thylthioprop-1-ene (1) and 3-methoxyprop-1-ene (2) molecules with participa tion of hydroxide ion was carried out by the RHF/6-31+G* and MP2/6-31+G//RH F/6-31+G* methods, Conformational isomerism of the initial molecules and re action products was considered. The distinctions are discussed in the spati al and electronic structure of intermediate carbanions stabilized (for 1) d ue to the negative hyperconjugation. Stationary points corresponding to com plexes between the molecules under study and the hydroxide ion and between the corresponding carbanion and water molecule were localized on the potent ial energy surfaces of the proton transfer reactions. For 2, the single-sta ge mechanism of prototropic rearrangement involving the H atom of the hydro xide ion was found to be more energetically preferable than the two-stage m echanism, whereas both mechanisms are expected to be equiprobable for 1.