Abstract

A systematic study of the tautomerism of 4-amino-1H-pyrido[2,3-c][1,2,6]thiadiazine 2,2-dioxide has been carried out. Thus, the relativity stability of the possible tautomers has been studied in the gas phase by ab initio and functional density theory (DFT) methods. The theoretical study in solution has been carried out using several continuum solvation models as self consistent reaction field (SCRF) and the Poisson-Boltzmann method. In addition, complexes with one or two molecules of water have been calculated in order to consider explicit solute-solvent interactions. These results have been compared with UV spectrophotometry data, giving good agreement between theoretical and experimental results in aqueous solution. Finally, the gauge invariant atomic orbital method (GIAO) for calculating magnetic absolute shielding with both the ab initio method (RHF/6-31G*) and density functional theory (B3LYP/6-31G*) have been applied to explore this method to study the tautomeric equilibrium in the pyrido[2,3-c][1,2,6]thiadiazine 2,2-dioxide system. (C) 2004 Elsevier B.V. All rights reserved.