The 1-deazapurine derivatives, tautomerism, substituent effect, and aromaticity: A computational study

► The stability, σ-and π-electron distribution, and aromaticity were studied for 1-deazapurines in the gas phase and water. ► The N9-H tautomer is always the most stable in the gas phase. ► In water, the N7-H and N9-H tautomers co-exist. ► The N3-H tautomer is always the least stable. ► The substituent effect combined with the three studied factors is discussed.