Synthesis, structural characterization, and computational study of (E)-N′-(3,4-dimethoxybenzylidene)furan-2-carbohydrazide

Abstract

An efficient synthesis of the new (E)-N′-(3,4-dimethoxybenzylidene)furan-2-carbohydrazide is described. Its molecular structural features have been characterized by FTIR, 1H NMR, 13C NMR and MS, then have been confirmed by single crystal X-ray diffraction. Quantum chemical calculations including molecular geometry, intermolecular H-bonds and vibrational frequencies were carried out for the structures to explain stability and geometry using the hybrid density functional (DFT/B3LYP) in conjunction with 6-311 + G(d,p) basis set. The calculated structural and vibrational parameters are presented and compared with their experimental X-ray and FTIR counterparts. The global minimum and local minima ground states characteristics of the title compound and its rotamers have been theoretically established through 2D potential energy scan and vibrational frequencies. Computational analysis predicted that head-to-tail E/E-dimer of the observed E-isomer has significantly stronger intermolecular hydrogen bonding in solution rather than in the gaseous state. It is found that NH and CO vibrational bands suffering blue-shift due to intermolecular hydrogen bonds (IHBs). Weak intramolecular hydrogen bonds that have been detected in the monomeric form in the gaseous state and in solution are lacking in trimers and tetramers due to loss of planarity in the molecular structure. Optimization in solution clearly shows that the strength of the IHBs decreased exponentially with dielectric continuum of the solvent used. Inexistence of solvent/monomer intermolecular hydrogen bonds has been explained in terms of Condensed Fukui Functions. Keywords: Hydrazones, DFT, Hydrogen bonds, Vibrational modes, Fukui functions