Ab initio MO calculations for the oxides, oxyacids, and oxyanions of S( IV ) and S( VI )

Ab initio molecular orbital (MO) calculations for two series of sulfur–oxygen compounds are reported: the S(IV) system of SO2, H2SO3, HSO , and SO , and the S(VI) system of SO3, H2SO4, HSO , and SO . Geometries about the sulfur atoms were optimized using the STO‐3G* basis set; energies at these geometries were computed by the STO−3G and 44‐31G basis sets both with and without five Gaussian d orbitals on S. The sulfur–oxygen bond lengths and the angles about the central atoms agree fairly well with experiment. The stabilization energy associated with the addition of the d orbitals was found to be a constant amount per bond (ca. 54 and 28 kcal mole−1 in the minimal and extended bases, respectively) in hypervalent compounds. The isomer HSO was predicted to be more stable than SO2(OH)−, but the reverse was true for HSO2(OH) compared to SO(OH)2. The deprotonation energies for the acids and the hydration energies for the oxides also were computed and discussed with reference to experimental data.