A comparative theoretical study of the effects of first- and second-row substituents in α-substituted carbanions

Abstract

This Paper reports the investigations we carried out on substituent effects in the carbanions H₂–X (where X = F, Cl, OH, or SH), using an ab initio SCF-MO treatment with three different basis sets of at least double zeta quality augmented with a set of diffuse p functions on carbon and with or without diffuse p functions and d polarization functions on the heteroatoms It was found that with all these substituents the carbanion centre is pyramidal, with inversion barriers that are larger than that of H₃, and which decrease in the order Cl > F > OH > SH. We also found that the order of stabilization energies is Cl > SH > F > OH. The 3d orbitals play a negligible role in determining the stabilization energies of H₂^–Cl and H₂^–SH. However, the 3d orbitals have a significant effect on the determination of some structural properties of H₂^–SH and H₂^–Cl.