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

Abstract

Extensive abinitio molecular orbital calculations on six sulfonyl radicals (XSO 2 where X = H, CH 3 , NH 2 , OH, F, and Cl), the simplest sulfinic acid HSO 2 H 3 and its isomeric sulfone H 2 SO 2 , the HSO 2 − anion of sulfinic acid, the isomeric anion SO 2 H − , and for completeness, the SO 2 H 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 SO 2 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 CH 3 SO 2 , NH 2 SO 2 , and OHSO 2 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 HSO 2 H, HSO 2 − , and SO 2 H than for the respective isomeric forms H 2 SO 2 , SO 2 H − , and HSO 2 .