Synthesis, molecular structure and spectral analysis of ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate: A combined experimental and quantum chemical approach

A new hydrazone, ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate (PDNBAH) has been synthesized and characterized by FT-IR, 1H NMR, UV–visible spectroscopy. All the quantum chemical calculations have been performed by density functional theory (DFT), using B3LYP functional and 6-31G(d,p) as basis set. The calculated and experimental wavenumber analyses confirm the existence of dimer of PDNBAH. The calculated binding energies of dimer using DFT and Bader's atoms in molecules (AIM) theory are −14.32 and −15.41 kcal/mol respectively. The intermolecular hydrogen bond energy of dimer due to the involvement of intermolecular hetero-nuclear double hydrogen bonds (NH⋯OC) through pyrrolic NH and CO of ester is also calculated to be equal to −12.29 kcal/mol using AIM calculation. The strength and the nature of hydrogen bonding and weak interactions in dimer have been analyzed by AIM theory in detail. The presence of resonance assisted hydrogen bonds (RAHB) has been confirmed by calculated ellipticity parameters using AIM calculation. The calculated thermodynamic parameters show that the reaction is non spontaneous at room temperature. The local reactivity descriptors show that C(13) is most reactive site for nucleophilic attack.

A new pyrrole containing hydrazone ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate (PDNBAH) has been synthesized and characterized by FT-IR, 1H NMR, UV–visible spectroscopy. All the quantum chemical calculations have been performed by DFT level of theory using B3LYP functional and 6-31G(d,p) as basis set. The calculated and experimental wavenumber analysis confirms the existence of dimer form of molecule. The calculated binding energies of dimer using DFT and AIM theory are −14.32 and −15.41 kcal/mol respectively. The presence of resonance assisted hydrogen bonds (RAHB) in sixteen membered pseudo ring has been confirmed by calculated ellipticity parameters using AIM program. The calculated thermodynamic parameters show reaction is non spontaneous at room temperature. The local reactivity descriptors show C(13) is the most reactive site for nucleophilic attack.Figure optionsDownload as PowerPoint slideHighlights
► FT-IR spectrum of PDNBAH was recorded and compared with the theoretical results.
► The theoretical calculations were made using DFT/B3LYP/6-31G(d,p) method.
► By using TD-DFT/6-31G method, electronic spectra for title compound have been 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.