Sulfonyl radicals, sulfinic acid, and related species: an abinitio molecular orbital study

Abstract

Extensive abinitio molecular orbital calculations on six sulfonyl radicals (XSO2 where X = H, CH3, NH2, OH, F, and Cl), the simplest sulfinic acid HSO2H3 and its isomeric sulfone H2SO2, the HSO2− anion of sulfinic acid, the isomeric anion SO2H−, and for completeness, the SO2H radical are presented. By use of the STO-3G* basis set, which includes d-type polarization functions on second-row atoms, all geometrical parameters are varied until the total energy is minimized, subject only to certain symmetry restrictions specified for each system. The inclusion of d orbitals on S is observed to affect the S—O bond lengths by as much as 0.45 Å. The calculations suggest that the radical site in sulfonyl radicals is significantly delocalized over the entire functional group and that the geometrical parameters of the SO2 functional group in sulfonyl radicals are nearly independent of the substituent (r(S—O) = 1.47 ± 0.01 Å, < OSO = 123 ± 2°). Estimates of the X—S bond energy in CH3SO2, NH2SO2, and OHSO2 are consistent with the chemistry of alkylsulfonyl and aminosulfonyl radicals and lead to an interesting prediction for alkoxylsulfonyl radicals. Furthermore the calculations yield lower total energies for HSO2H, HSO2−, and SO2H than for the respective isomeric forms H2SO2, SO2H−, and HSO2.