Synthesis, molecular structure, multiple interactions and chemical reactivity analysis of a novel ethyl 2-cyano-3-[5-(hydrazinooxalyl–hydrazonomethyl)-1H-pyrrol-2-yl]-acrylate and its dimer: A combined experimental and theoretical (DFT and QTAIM) approach

A detailed spectroscopic analyses of a newly synthesized ethyl 2-cyano-3-[5-(hydrazinooxalyl–hydrazonomethyl)-1H-pyrrol-2-yl]-acrylate (3) have been carried out using 1H and 13C NMR, UV–Visible, FT-IR and mass spectroscopic techniques. All the quantum chemical calculations have been carried out using DFT level of theory, B3LYP functional and 6-31G(d,p) as basis set. The 1H and 13C NMR chemical shifts are calculated using gauge including atomic orbitals (GIAOs) approach in DMSO-d6. TD-DFT is used to calculate the energy (E), oscillatory strength (f) and wavelength absorption maxima (λmax) of various electronic transitions and their nature within molecule. Natural bond orbital (NBO) analysis is carried out to investigate the various intra and intermolecular interactions in dimer and their corresponding second order stabilization energy (E(2)). A combined theoretical and experimental vibrational analysis confirms the existence of dimer and the binding energy of dimer is calculated as 9.21 kcal/mol using DFT calculations. To determine the energy and nature of different interactions topological parameters at bond critical points (BCPs) have been analyzed by Bader’s ‘atoms in molecules’ (AIMs) theory in detail. Electrophilic charge transfer (ECT) is calculated to investigate the relative electrophilic or nucleophilic behavior of reactant molecules involved in chemical reaction. Global electrophilicity index (ω = 5.5836 eV) shows that title molecule (3) is a strong electrophile. The local reactivity descriptors such as Fukui functions ( f k + , f k - ) , local softness ( s k + , s k - ) and electrophilicity indices ( ω k + , ω k - ) analyses are performed to determine the reactive sites within molecule.