Semiempirical and ab initio study of the nature of the C-S bond in sulfonium ylides

Abstract

The importance of d-orbitals for the interpretation of properties of sulfonium ylides is demonstrated on the basis of semiempirical and ab initio calculations. The calculated C-S bond length values are sensitive to inclusion of d-orbitals into the AO basis set. Even a high quality basis (4-31 G) without d-orbitals leads to C-S bond lengths which are significantly larger than the experimental ones whereas bases including d-orbitals afford satisfactory agreement. Inclusion of d-orbitals results in charge reduction on the atoms C and S and in a substantially increased order of the bond between these atoms. The decrease of total energy which results from inclusion of d-orbitals is related to (d-p)π bonding overlap between the atoms S and C.