MOLECULAR MODELING OF THE ISOTHIAZOLO[5,4-B]PYRIDIN-3(2H)-ONE DERIVATIVES

The performance of several semiempirical (MNDO, AM1, PM3, and SAM1) an d ab initio (HF and MP2/6-31G) methods for describing the structural and electronic features of a series of isothiazolopyridines, some of t hem bearing a hypervalent sulphur, is compared. Most of semiempirical methods calculate reasonable molecular structures, as compared with X- Ray structures, even in the case of S-oxides and S,S-dioxides. However , dipole moments are barely reproduced by these methods, even in the c ase of SAM1, which includes d orbitals. Hartree-Fock ab initio calcula tions do not lead to good dipole moment values in the case of S,S-diox ides. The agreement with experimental values is much better in the cas e of second order Moller-Plesset calculations, but this seems to be du e to the systematic differences found between HF and MP2 values. (C) 1 996 Elsevier Science Ltd