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)2NH2 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)2NH2, ClS(O)2NH2 and FS(O)2NH2. 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.