Investigation of the structure of and the properties of the potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo[3,4-d]pyridazine-1,4-diones in the gaseous and aqueous phases using the AM1 semi-empirical method

Potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo3,4-d]pyridazine-1,4-diones and their fixed tautomeric forms have been studied in order to predict their tautomeric equilibrium constants and pK_a values using semi-empirical AM1 quantum-chemical calculations at the SCF level in the gas phase and in aqueous solution. Hydroxy-oxo forms were found to be more stable than dioxo and dihydroxy forms. The results obtained from the tautomeric equilibria and basicity calculations are in good agreement with experimental data.