Synthesis, molecular structure and spectral analysis of ethyl 4-formyl-3,5-dimethyl-1H-pyrrole-2-carboxylate thiosemicarbazone: A combined DFT and AIM approach

A new ethyl 4-formyl-3,5-dimethyl-1H-pyrrole-2-carboxylate thiosemicarbazone (EFDMPCT) has been synthesized and characterized by elemental analysis and FT-IR, 1H NMR, UV–Visible, DART-mass spectroscopy. Quantum chemical calculations have been performed by DFT level of theory using B3LYP functional and 6-31G (d,p) as basis set. The calculated 1H NMR chemical shifts using gauge including atomic orbitals (GIAO) approach are in good agreement with the observed chemical shifts. The electronic transitions within molecule have been interpreted using the time dependent density functional theory (TD-DFT). The calculated and experimental wavenumbers analyses confirm the existence of dimer. Topological parameters electron density, Laplacian of electron density, kinetic electron energy density, potential electron density and the total electron energy density at the bond critical points (BCP) analyzed using ‘Atoms in Molecules’ AIM theory reveals intra and inter molecular hydrogen bonding other weaker interactions in detail. The calculated intermolecular hydrogen bond energy of dimer is −12.2176 kcal/mol using AIM calculation. The results of AIM ellipticity confirm the existence of resonance assisted hydrogen bonds in dimer. The calculated thermodynamic parameters show that reaction is exothermic and non-spontaneous at room temperature. The local reactivity descriptors find the reactive sites within molecules have been calculated.

► FT-IR spectrum of EFDMPCT is recorded and compared with the theoretical results.
► The resonance assisted intermolecular hydrogen bonds are characterized using AIM calculations.
► By using TD-DFT/6-31G method, electronic transitions for title compound are predicted.
► The 1H NMR spectrum has also been calculated using GIAO method.
► Chemical reactivity has been explained with the aid of global and local electronic descriptors.