Spectrochimica Acta Part A 92 (2012) 295–304 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy j ourna l ho me page: www.elsevier.com/locate/saa Molecular structure, heteronuclear resonance assisted hydrogen bond analysis, chemical reactivity and first hyperpolarizability of a novel ethyl-4-{[(2,4- dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate: A combined DFT and AIM approach R.N. Singh ∗ , Amit Kumar, R.K. Tiwari, Poonam Rawat, Vikas Baboo, Divya Verma Department of Chemistry, University of Lucknow, University Road, Lucknow 226007, India a r t i c l e i n f o Article history: Received 2 December 2011 Received in revised form 4 February 2012 Accepted 22 February 2012 Keywords: DFT Hydrogen bonded dimer AIM Ellipticity Reactivity descriptor NLO a b s t r a c t A new ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate (EDPHEDPC) has been synthesized and characterized by FT-IR, 1 H NMR, UV–vis, DART-Mass spec- troscopy 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 1 H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO as solvent. The time dependent density functional theory (TD-DFT) is used to find the various electronic transitions and their nature within molecule. A combined theoretical and experimental wavenumber analysis confirms the existence of dimer. Topological parameters such as electron density ( BCP ), Laplacian of electron density (▽ 2  BCP ), kinetic electron energy density (G BCP ), potential electron density (V BCP ) and the total electron energy density (H BCP ) at bond critical points (BCP) have been analyzed by Bader’s ‘Atoms in molecules’ AIM theory in detail. The intermolecular hydrogen bond energy of dimer is calculated as -12.51 kcal/mol using AIM calculations. AIM ellipticity analysis is carried out to confirm the presence of resonance assisted intra and intermolecular hydrogen bonds in dimer. The calculated thermodynamic parameters show that reaction is exothermic and non-spontaneous at room temperature. The local reactivity descriptors such as Fukui functions (f k + , f k - ), local softnesses (s k - , s k + ) and electrophilicity indices (ω k + , ω k - ) analyses are performed to determine the reactive sites within molecule. Nonlinear optical (NLO) behavior of title compound is investigated by the computed value of first hyperpolarizability (ˇ 0 ). © 2012 Elsevier B.V. All rights reserved. 1. Introduction Hydrazones are an important class of compounds due to their various properties and applications. They are versatile starting materials for the synthesis of a variety of N, O or S containing heterocyclic compounds such as oxadiazolines, thiazolidinones, tri- azolines, and various types of other organic compounds [1–7]. Due to the presence of 〉N N C〈 functional frame, [2 + 2] cycloaddi- tions and 1,3 dipolar cycloadditions with hydrazones have been turned into a valuable tool for the synthesis of azetidinones and pyrazoles respectively [8,9]. Hydrazones having an azomethine proton CH N NH constitute an important class of compounds for new drug development [10–14]. They are mainly used as ∗ Corresponding author. Mobile: +91 9451308205. E-mail address: rnsvk.chemistry@gmail.com (R.N. Singh). antimicrobial, antitubercular [15–19] and antidiabetic agents [20]. They have also been used as potentially DNA damaging and muta- genic agents [21,22]. They have strong coordinating ability towards different metal ions [23,24]. In addition, aroyl hydrazones and their mode of chelation with transition metal ions present in the living system have been of significant interest [25,26]. The anion recep- tor 2,4-dinitrophenylhydrazone of pyrrole--carboxaldehyde has been used for the development of potential chemosensors [27]. The chemical stability of hydrazones and their high melting points have recently made them attractive as prospective new materials for opto-electronic applications [28]. The nitro phenyl hydrazones exhibit a series of good organic nonlinear optical (NLO) proper- ties [29–31]. In particular, the interest to this compound is being due to the above applications and fact that the pyrrole fragment is a constituent of many biological systems. In order to obtain information for significant application about pyrrole containing 2,4-dinitrophenylhydrazones, the title compound is synthesized 1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2012.02.086