Ab initio and DFT studies on tautomerism of indazole in gaseous and aqueous phases

Abstract

Ab initio and DFT methods have been used to study the five tautomeric forms of indazole (IZT1, IZT2, IZT3, IZT4, IZT5) in gaseous and aqueous phases. The tautomers in gas phase have been optimized at MP2/6-311G(2d,2p), B3LYP/6-311G(2d,2p) and B3PW91/6-311G(2d,2p) levels of theory. The self-consistent reaction field theory (SCRF) has been used 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 were compared and analyzed both in gaseous and aqueous phases. The principle of maximum hardness has been tested by calculating chemical hardness and chemical potential at HF/6-311G(2d,2p) level of theory to predict the order of stability of the tautomers. The condensed Fukui functions have been calculated to identify the relative change in most reactive site of the optimized tautomers in gas phase using atomic charges obtained through Mulliken population analysis scheme. 13C-NMR studies have been carried out for these tautomers in the gas phase at B3LYP/6-311G(2d,2p) level of theory on the basis of Cheeseman co-worker's method and the results were discussed.