Molecular structural conformations and hydration of internally hydrogen‐bonded salicylic acid: Ab initio and DFT studies

Abstract

AbstractWe studied molecular structural conformations and hydration of internally hydrogen‐bonded salicylic acid using ab initio and density functional theory methods. Molecular geometries and energetical parameters were obtained in gaseous phase using MP2 and B3LYP levels of theory, implementing the 6‐311G(2d,2p) atomic basis set. Chemical hardness and chemical potential were calculated at HF/6‐311G(2d,2p) level of theory for all the optimized structures, and the principle of maximum hardness was tested. The condensed Fukui functions were calculated using the atomic charges obtained through a natural population analysis scheme for all optimized structures at B3LYP/6‐311G(2d,2p) level of theory, and the most reactive sites of the molecules were identified. NMR studies were carried out for all the conformers in gaseous phase on the basis of Cheeseman et al.'s method at B3LYP/6‐311G(2d,2p) level of theory; the calculated chemical shift values are discussed. The self‐consistent reaction field theory (SCRF) was used to optimize all the conformers in aqueous phase (ε = 78.39) at B3LYP/6‐311G(2d,2p) level of theory and the solvent effect was studied. The geometrical and energetical parameters of all the conformers are compared and analyzed. The dimeric structure of the most stable conformer in the gaseous phase was optimized at B3LYP/6‐311G(2d,2p) level of theory and the interaction energy studied. Selected conformers were allowed to interact with water molecule; optimized parameters are discussed. Vibrational frequency analyses were performed at MP2/6‐311G(2d,2p) level of theory and the stationary point corresponding to local minima without imaginary frequencies are obtained for all the optimized structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005