Bonding in carbonyl and thiocarbonyl compounds: an ab initio charge density study of H 2CX and HC(X)YH (X,Y  O or S)

Abstract

Ab initio 6–31 G ∗ SCF-MO calculations have been carried out for formaldehyde, thioformaldehyde, and for both the s-cis and s-trans conformers of formic acid and their sulphur-containing analogues (thiol-, thiono- and dithioformic acids). The calculated wavefunctions were used to perform a detailed charge density analysis based on both the Mulliken and Bader partitioning schemes. Particular emphasis was given to the study of the effects of substitutions of oxygen-by-sulphur on the electronic distributions of the whole set of molecules and to the conformational effects due to the s-cis → s-trans rotamerization in the acids and thiolacids studied. The calculated electronic properties are successfully correlated with several geometric features exhibited by the molecules and used to explain the relative differences in energy between the s-cis and s-trans forms in formic acid and its sulphur derivatives.