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

The substituent effect on the 1-deazapurine system energetic, tautomerism, σ- and π-electron distribution in valence orbital and aromaticity were studied by means of the B3LYP/cc-pVTZ calculations. Regardless the substituent and the substitution site the most stable in the gas phase is the N9–H tautomer and the least stable is the N3–H one. In water, the N9–H and N7–H tautomers are expected to co-exist in equilibrium. The σ and π valence orbital population in the two rings of the 1-deazapurine system, and the two media, were meticulously considered for all the substituents. The aromaticity indices are in line with weaker stability of the N3–H tautomer and domination of the N9–H form over the N7–H one.