Probing the compound (E)-2-[(4-bromophenylimino)methyl]-6-ethoxyphenol mainly from the point of tautomerism in solvent media and the solid state by experimental and computational methods

Abstract

In this study, (E)-2-[(4-bromophenylimino)methyl]-6-ethoxyphenol compound was investigated by mainly focusing on stacking interactions assembling the supramolecular network of the compound and on tautomerism in solvent media and in the solid state. In doing so. the molecular structure and spectroscopic properties of (E)-2-[(4-bromophenylimino)methyl]-6-ethoxyphenol were experimentally characterized by X-ray diffraction, FT-IR. NMR and UV/Vis spectroscopic techniques and computationally by DFT method. The X-ray diffraction and FT-IR analyses of the title compound reveal the existence of enol form in the solid state. The non-covalent C-H center dot center dot center dot pi and inter-molecular hydrogen bonding interactions assemble the supramolecular structure of the title compound by forming 4-connected (4,4)-net in Wells nomenclature. The dependence of tautomerism on solvent types was studied on the basis of UV/Vis spectra recorded in different organic solvents. The results showed that the title compound exists in enol form in all solvents. Computational investigation of enol-keto tautomerism was carried out at B3LYP (6-311G(d,p)) level for both enol and keto forms. The results obtained for enol form are more compatible to the experimental results than those of keto form. TD-DFT calculations carried out in both gas and solution phases indicate that the title compound adopt only enol form in solution. The enol-keto tautomerism was also investigated by evaluating the changes in thermodynamic properties (heat capacity, entropy, enthalpy and Gibbs free energy) with varying temperatures, showing that the formation of tautomerism in the title compound is non-spontaneous between 100 and 500 K and that the title compound must exist in enol form. (C) 2011 Elsevier B.V. All rights reserved.