Ab initio DFT study of the rotation barriers and competitive hydrogen bond energies (in gas phase and water solution) of 2-nitroresorcinol, 4,6-dinitroresorcinol and 2-nitrophenol in their neutral and deprotonated conformations

摘要

The intramolecular hydrogen bonds of 2-nitroresorcinol, I, 4,6-dinitroresorcinol, II and 2-nitrophenol, III, have been studied, in gas phase and in water solution, at ab initio level using the DFT-B3LYP approach and the 6-31G~** basis set. The strength of the hydrogen bridges has been evaluated according to the classic procedure and by comparing the barriers to internal rotation of the studied compounds and those of nitrobenzene, phenol and resorcinol. The anions deriving from mono- and double-deprotonation were also taken into account to evidence the role of the hydrogen bridge in damping the relevant O~...O intramolecular repulsive interactions The investigation in water solution was carried out by means of the PCM-SCRF method. The obtained results do not reveal particularly important variations in the geometrical parameters with respect to those of the gas phase, but non-negligible changes occurs in the net charge densities, bond electron population and hydrogen bond energies. ΔG_(solv) and deprotonation energies are also reported.