ATOMIC CHARGES DERIVED FROM DIFFERENT METHODS - A COMPARATIVE-STUDY APPLIED TO SO2 HETEROCYCLES

Atomic charges were calculated at ab initio level using different meth ods of charge determination to compare them and estimate their utility in the electronic description of heterocycles containing the SO2 moie ty. Those procedures implemented on the Gaussian92 program were includ ed [Mulliken population analysis, Weinhold-Reed natural population ana lysis (NPA) and CHELPG]. The first two are based on the molecular orbi tals while in the third one the charges are derived by fitting the ele ctrostatic potential. Two sets of compounds were chosen to represent t he different characteristics of the SO2 heterocycles studied: simpler five-member heterocycles and SO2 small derivatives. These molecules we re optimized at the HF/6-31G level and their energy evaluated by a pu nctual calculation MP2/6-31G//HF/6-31G*. The dipole moments for these molecules were obtained by using all the methods previously mentioned and compared with the SCF, MP2, and experimental dipole moments. The influence on the charges of some atoms by changing the electronegativi ty of neighboring atoms has also been investigated for these compounds . The results obtained show that the best methods to describe the elec tronic distribution of the oxathiole studied are Mulliken and CHELPG a t the MP2 level of calculation. The charge distributions obtained with these two methods for these particular heterocycles are discussed. (C ) 1997 John Wiley & Sons, Inc.