Post Hartree–Fock and density functional theory studies on Di-Protonated Allopurinol

Post Hartree–Fock and density functional theory (DFT) methods have been employed to study the molecular properties of Di-Protonated Allopurinol²⁺ tautomers in gaseous and aqueous phase environments. The tautomers in gaseous phase have been optimized at MP2/6-311G(2d,2p) and B3LYP/6-311G(2d,2p) levels of theory. The self-consistent reaction field theory (SCRF) has been employed to optimize the tautomers in aqueous phase (ε = 78.5) at B3LYP/6-311G(2d,2p) level of theory and the solvent effect has been studied. The structure, energetics and relative stabilities of the tautomers have been analyzed both in gaseous and aqueous phases. The principle of maximum hardness (MHP) has been tested at B3LYP/6-311G(2d,2p) level of theory. The condensed Fukui functions have been calculated using the atomic charges obtained through Natural population analysis to identify the relative change in the most reactive site of the optimized structures. NMR studies have been carried out, on the basis of Cheeseman coworker’s method, to analyze the molecular environment as well as the delocalization activities of electron clouds.