Solvent effect on the tautomerism of 4-aminopyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides
A detailed study of the tautomerism of 4-amino-1H-pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide has been carried out using different theoretical methods. Semiempirical, molecular orbital and density functional theory based ab initio methods have been used to study all the possible tautomers of this compound in the gas phase. Several continuum solvation models have been used to estimate the relative stability of the tautomers in water. Complexes with one and two molecules of water have been considered to take into account the specific solute–solvent interactions. Finally, these results have been compared with UV spectrophotometry data, giving good agreement between theoretical and experimental results in aqueous solution.