Molecular modelling of the isothiazolo[5,4-b]pyridin-3(2H)-one derivatives

Article abstract of DOI:10.1016/0040-4020(96)00443-7

The performance of several semiempirical (MNDO, AM1, PM3, and SAM1) and ab initio (HF and MP2/6-31G*) methods for describing the structural and electronic features of a series of isothiazolopyridines, some of them 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 case of SAM1, which includes d orbitals. Hartree-Fock ab initio calculations do not lead to good dipole moment values in the case of S,S-dioxides. The agreement with experimental values is much better in the case of second order Moller-Plesset calculations, but this seems to be due to the systematic differences found between HF and MP2 values.