Abstract The compounds CH3XCH3 (1), CH3XCF3 (2), C6H5XCF3 (3) and C6H5XC6H5 (4), where X: a, S(O), b, S(NSO2CF3), c, SO2, d, S(O)NSO2CF2, e, S(NSO2CF3)2, were studied by 1H, 13C, and 19F NMR spectroscopy and by MO-SCF method in MNDO-PM3 valence approximation. The peculiarity of the structure of the X group is a deficiency of electron density on the sulfur atom and a high negative charge on the neighboring O and N atoms. The S-N bond polarity is higher than that of the S-O bond. The S-N bond index is nearly unity (1b 1.06, 1d 0.98, 1e 1.02) and is lower than for the S-O bond (1a 1.24, 1c 1.19). Hence, the S-O and S-N bonds in 1-4 cannot be considered as double ones. They are strongly polarized with a prevailing contribution of the electrostatic component, the covalent contribution being low. In compounds with NSO2CF3 groups total electronic charge on the X group is higher than in 1a-4a and 1c-4c. As a consequence, total electronic charge on the CH3, CF3 and C6H5 groups is lower in compounds 1-4b, d, e than...