L. Senthilkumar, P. Kolandaivel
Oct 24, 2003
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Journal
Journal of Molecular Structure-theochem
Abstract
Abstract In the present investigation, the tautomerism of 6-thioxanthine molecules have been studied using ab initio and density functional theory methods in gas phase. The relative energies of these tautomers were calculated at HF, MP2, B3LYP, B3PW91 level of theory using 6-31G* basis set. Further, the tautomers were studied in aqueous phase ( e =78.5) using Tomasi's polarisable continuum model (PCM) at HF, B3LYP, and B3PW91 levels of theory. The relative energy value indicates that tautomer 6TX9 is the most stable tautomer in both gas and aqueous phases at all the levels of theory. The chemical hardness studies show the failure of Maximum Hardness Principle to predict most stable tautomer and order of stability in both gas and aqueous phases due to the intra molecular interactions. 13 C NMR studies were carried out on these tautomers on the basis of cheeseman coworker's method [J. Chem. Phys. 104 (1996) 5497] and the results are discussed. The condensed Fukui functions have been calculated using the atomic charges of Mulliken population analysis scheme for the tautomers in gas and aqueous phases. The calculated condensed Fukui function values predict the reactive site of 6-thioxanthine tautomers for positron, electron and radical attacks in both gas and aqueous phases.