Semi-empirical atomic charges and dipole moments in hypervalent sulfonamide molecules: descriptors in QSAR studies

The Mulliken and ESP-based atomic charges and dipole moments have been calculated for a group of substituted methanesulfonamides by several ab initio and semi-empirical methods, in order to find the most reliable semi-empirical method of calculating these quantities in hypervalent molecules. It was found that the ab initio Mulliken charges on the sulfonamide H were meaningless,and that the ab initio ESP-based atomic charges calculated using any non-minimal basis set well reproduced the dipole moments. The semi-empirical results were less satisfactory, but in general, the ESP-based charges were more promising than the Mulliken charges, and CNDO-based dipole moments agreed better with ab initio dipole moments than with those calculated by AM1 or PM3. All charges for hypervalent molecules such as sulfonamides, calculated with semiempirical methods, should be treated with caution. (C) 1998 Elsevier Science B.V.