Experimental and theoretical study of 4-formyl pyrrole derived aroylhydrazones

• The DFT methods have been used for computational study.
• Theoretical FT-IR spectra of the studied compounds was compared with the experimental results.
• Experimental 1H NMR chemical shifts have been compared with theoretical results.
• Chemical reactivity has been explained with the aid of global and local electronic descriptors.

Two new 4-formyl pyrrole derived aroylhydrazones (3a, b) from ethyl 4-formyl-3,5-dimetyl-1H-pyrrole-2-carboxylate and aroylhydrazides (3,5-dinitrobenzohydrazide/2-hydrazinocarbonyl-N-phenyl-acetamide) have been synthesized and characterized by various spectroscopic techniques 1H NMR, Mass, UV–Visible and FT-IR. The calculated thermodynamic parameters show that the formation of 3a as spontaneous, whereas 3b as non-spontaneous. TD-DFT has been used to calculate the absorption wavelengths, oscillator strength (f) and the nature of electronic excitations. Natural bond orbital (NBO) analysis has been carried out to explore the various conjugative and hyperconjugative interactions and their second order stabilization energy (E(2)) within monomer and its dimer. The dimer formation of 3a, 3b due to result of intermolecular hydrogen bonding N1H30⋯O84, N1H28⋯O60 is obvious in 1H NMR, NBO and FT-IR as down field chemical shifts, n(O84) → σ∗(N1H30), n(O60) → σ∗(N1H28) interactions, vibrational red shifts, respectively. To determine the strength and nature of hydrogen bonding, topological parameters at bond critical points (BCP) have been analyzed by ‘Quantum theory of Atoms in molecules’ (QTAIM) in detail. The global electrophilicity index (ω) has been calculated to determine the relative electrophilic strength of molecules. The local reactivity descriptors analyses such as Fukui functions (fk+, fk−), local softnesses (sk+, sk−) and electrophilicity indices (ωk+, ωk−) have been performed to determine the reactive sites within molecules. The first hyperpolarizabilities (β0) of 3a, b have been computed to evaluate the non-linear optical (NLO) response of the investigated molecules.

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