Theoretical studies on S-N interactions in sulfonamides

Theoretical studies using ab initio molecular orbital and density functional methods have been carried out on sulfonamide HS(O)(2)NH2 to understand the S-N interactions present in the sulfonamide. Complete optimisation at HF/6-31+G*, MP2/6-31+G* and B3LYP/6-31+G* levels have shown that the NH2 and SO2 units are in an eclipsed arrangement. The effect of substituent on the S-N interactions has been analysed by studying, CH3S(O)(2)NH2, CIS(O)(2),NH2 and FS(O)(2)NH2. Natural bond orbital analysis has been carried out to understand various interactions present in these systems. The S-N rotational barrier obtained using G2MP2 method is 6.74 kcal/mol which has been found to be more due to the repulsive interactions than the anomeric interactions. (C) 2002 Published by Elsevier Science Ltd.