Molecular structure, spectral studies, intra and intermolecular interactions analyses in a novel ethyl 4-[3-(2-chloro-phenyl)-acryloyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate and its dimer: A combined DFT and AIM approach

A newly synthesized chalcone, Ethyl 4-[3-(2-chloro-phenyl)-acryloyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate (ECPADMPC) has been characterized by 1H NMR, 13C NMR, UV–Vis, FT-IR, Mass spectroscopy and elemental analysis. Quantum chemical calculations have been performed by DFT level of theory using B3LYP functional and 6-31G(d,p) as basis set. The time dependent density functional theory (TD-DFT) is used to find the various electronic transitions within molecule. A combined theoretical and experimental wavenumber analysis confirms the existence of dimer. Topological parameters-electron density (ρBCP), Laplacian of electron density (▿2ρBCP), energetic parameters-kinetic electron energy density (GBCP), potential electron density (VBCP) and the total electron energy density (HBCP) at the bond critical points (BCP) have been analyzed by ‘Atoms in molecules’ AIM theory in detail. The intermolecular hydrogen bond energy of dimer is calculated as −12.3 kcal/mol using AIM calculations. AIM ellipticity analysis is carried out to confirm the presence of resonance assisted intermolecular hydrogen bonds in stabilization of dimer. The analysis clearly depicts the presence of different kind of interactions in dimer. This dimer may work as model system to understand the H-bonding interaction in biomolecules. The local reactivity descriptor analysis is performed to find the reactive sites within molecule.

Graphical abstractEthyl 4-[3-(2-chloro-phenyl)-acryloyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate (ECPADMPC) chalcone has been synthesized and characterized by 1H NMR, 13C NMR, UV–Vis, FT-IR, Mass spectroscopy and elemental analysis. Quantum chemical calculations have been performed by DFT level of theory using B3LYP functional and 6-31G(d,p) as basis set. A combined theoretical and experimental wavenumber analysis confirms the existence of dimer. Topological parameters such as electron density (ρBCP), Laplacian of electron density (▿2(ρBCP)), kinetic electron energy density (GBCP), potential electron density (VBCP) and the total electron energy density (HBCP) at the bond critical points (BCP) have been analyzed by Bader's ‘Atoms in molecules’ AIM theory in detail. The local reactivity descriptor analysis is performed to find the reactive sites within molecule. The calculated thermodynamic parameters show that reaction is endothermic and non-spontaneous at room temperature.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► FT-IR spectrum of ECPADMPC was recorded and compared with the theoretical result. ► All the theoretical calculations were made using DFT/B3LYP/6-31G(d,p) method. ► By using TD-DFT/6-31G method, electronic absorption spectrum of title compound has been predicted. ► The 1H NMR spectrum has also been calculated using GIAO method. ► Chemical reactivity has been explained with the aid of electronic descriptors.