Experimental and theoretical study of 4-formyl pyrrole derived aroylhydrazones

Journal of Molecular Structure 1084 (2015) 326–339

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Experimental and theoretical study of 4-formyl pyrrole derived aroylhydrazones Poonam Rawat, R.N. Singh ⇑ Department of Chemistry, University of Lucknow, Lucknow 226007, U.P., India

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The DFT methods have been used for

computational study.  Theoretical FT-IR spectra of the

studied compounds was compared with the experimental results. 1  Experimental H NMR chemical shifts have been compared with theoretical results.  Chemical reactivity has been explained with the aid of global and local electronic descriptors.

a r t i c l e

i n f o

Article history: Received 1 November 2014 Received in revised form 13 December 2014 Accepted 14 December 2014 Available online 20 December 2014 Keywords: Aroylhydrazone NBO Hydrogen bonding QTAIM Electronic descriptor First hyperpolarizability

a b s t r a c t Two new 4-formyl pyrrole derived aroylhydrazones (3a, b) from ethyl 4-formyl-3,5-dimetyl-1H-pyrrole2-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 N1AH30  O84, N1AH28  O60 is obvious in 1H NMR, NBO and FT-IR as down field chemical shifts, n(O84) ? r⁄(N1AH30), n(O60) ? r⁄(N1AH28) 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 (x) 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 (xk+, xk) have been performed to determine the reactive sites within molecules. The first hyperpolarizabilities (b0) of 3a, b have been computed to evaluate the non-linear optical (NLO) response of the investigated molecules. Ó 2014 Elsevier B.V. All rights reserved.

Introduction

⇑ Corresponding author. Tel.: +91 9451308205. E-mail address: [email protected] (R.N. Singh). http://dx.doi.org/10.1016/j.molstruc.2014.12.045 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

Aroylhydrazones are special group of compounds in the Schiff bases family due to their wide applications in chemistry, biology and characterized by the presence of frame ˜C@NANHACOA having

P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339

two inter-linked nitrogen atoms in different hybridization states as Nsp2ANsp3. They are found to be good synthons for the target syntheses of 1,3,4-oxadiazine, 1,2,4-triazine, pyrazole derivatives [1] and 1,3,4-oxadiazolines, 2-azetidinones, 4-thiazolidinones via heterocyclic transformations [2,3]. Several aroylhydrazones have wide applications in the field of analytical chemistry as a selective metal extracting agent as well as in spectrophotometric determination of certain transition metals [4–6]. However, the most valuable property of aroylhydrazones is their great physiological activity due to the presence of the active pharmacophore (˜C@NANHACOA) and provides a wide range of application in medicinal and pharmaceutical fields with various biological applications. Therefore, a number of hydrazone derivatives have been used for the treatment of diseases such as convulsant [7], malaria [8], HIV, cancer [9], microbial [10–12] and tuberculosis [13–15]. Tuberculosis activity is attributed to the formation of stable chelates with transition metals present in the cell. Thus many vital enzymatic reactions catalyzed by these transition metals cannot take place in the presence of hydrazones [16]. Many of hydrazones are used as prospective new materials for the development of potential chemosensors [17], opto-electronic [18] and non-linear optical (NLO) [16–18] applications. Heteroatoms influence various properties of material and their applications [19–21]. Materials with excellent optical non-linearity and certain spectral characteristics are required for high-level technologies such as data storage, information processing, telecommunications and optical switching. Organic materials with p-extended frameworks exhibit photoluminescence and used for organic light emitting devices (OLEDs) [22]. Organic compounds are also important for photonic devices because of their strong optical non-linear properties [23]. Photoluminescence, the phenomenon of luminescence or light emission caused by the absorption of optical radiation, is widely used to characterize many chemical, physical and biological processes [24,25]. Hydrogen bonds are of versatile importance in fields of chemistry and biochemistry, which governs chemical reactions, supramolecular structures, molecular assemblies and life processes. Hydrogen bonds are classified into two categories as: (i) conventional or red shift (ii) improper or blue shift hydrogen bonds, depending upon the nature of atoms involved in the hydrogen bridges [26–28]. Therefore, the above pyrrole aroylhydrazones 3a and 3b have been synthesized and characterized using various experimental spectroscopic methods and theoretical calculations. In present paper, structural properties, spectroscopic analysis, intramolecular conjugative and hyperconjugative interactions, inter- and intramolecular hydrogen bonding, chemical reactivity and NLO properties have also been investigated.

Results and discussion Thermochemistry For simplicity, the reactants are abbreviated as 1, 2a, b, products 3a, b and byproduct water 4, respectively. The reactions involved in the formation of product molecules 3a, b are abbreviated as Reactions 1, 2, respectively. The calculated thermodynamic parameters as Enthalpy (H), Gibbs free energy (G) and Entropy (S) of 1; 2a, b; 3a, b; 4 and their change (DH, DG, DS) for Reactions 1, 2, are listed in Supplementary Table S1, respectively. For Reaction 1, the calculated negative values of enthalpy change (DH) and Gibbs free energy (DG) change of reaction show that title reactions is exothermic and spontaneous at room temperature. For Reaction 2, the positive value of (DH) shows that reaction is endothermic. The reaction 2 undergoes in the presence of catalyst

327

which lowers down the activation energy barrier and change the reaction rate to speed up the reaction. The calculated thermodynamic parameters of monomer (M), dimer (D) of 3a, b and their change for Dimerization reaction, at 25 °C are listed in Supplementary Table S2. For dimer formation, the negative values of enthalpy change (DH) and Gibbs free energy change (DG) indicate that the dimer formation is exothermic and spontaneous at room temperature. Thermodynamic equilibrium constant (Keq) for the dimerization Reaction 1, 2 is calculated as 275.5, 45.4, respectively, at room temperature. The high value of equilibrium Keq between monomer and dimer shows that dimer formation is more favored. Molecular geometry Optimized geometry of all the reactants 1, 2a, b, products 3a, b and byproduct water 4 involved in chemical reactions are shown graphically in Supplementary Scheme S1. The optimized geometry for the ground state conformer of 3a, b is shown in Fig. 1. Selected optimized geometrical parameters of 3a, b calculated at B3LYP/ 6-31G(d,p) are listed in Supplementary Table S3. The ground state lower energy conformer of both molecules 3a, b possesses C1 symmetry. The E-configuration about the Schiff base C7@N10 bond with respect to the pyrrole and ANHACOA group gives lower energy conformer. The E-configuration about Schiff base C7@N10 bond is not only observed in our theoretical study but also reported in crystal structure of various aroylhydrazone derivatives [29,30]. In 3b, the skeleton of whole molecule is approximately planner (maximum deviation up to 3.1° in dihedral angle) except the dihedral angles (N11AC12AC14AC19) and (C12AC14AC19AN21) associated with the C14 carbon atom of hydrazide CH2 group. These dihedral angles are 130.3°, 38.0°, respectively. In both 3a, b, the asymmetry of the N1AC2 and N1AC5 bonds i.e. difference between their bond lengths can be explained due to the presence of the two different groups as ‘ethoxycarbonyl’ and ‘methyl’ at C2 and C5, respectively. It leads to the elongation of N1AC2 bond. These effects are not only in quantum calculation but also reflect in crystal structure of the Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate [31], methyl 4-p-tolyl-1H-pyrrole-2-carboxylate [32]. Optimized geometry for dimer of the lowest energy ground state conformer of 3a, b is shown in Fig. 2x, y, respectively. In dimer, heteronuclear intermolecular hydrogen bonding (NAH  O) between pyrrolic (NAH) and carbonyl (C@O) oxygen of ester form two hydrogen bonds. In intermolecular hydrogen bonds, the NAH bond acts as proton donor and C@O bond as proton acceptor. According to the Etter terminology [33], the cyclic ester dimer form the ten member pseudo ring denoted as R22(10) or more extended sixteen member pseudo ring R22(16). The superscript designates the number of acceptor centers and subscript, the number of donors in the motif. In dimer of 3a and 3b, due to intermolecular hydrogen-bond formation both proton donor (NAH bond) and proton acceptor (C@O bond) are elongated from 1.010 Å to 1.020 Å, 1.223 Å to 1.231 Å, respectively. Total energy of the monomer (M) and its dimer (D) for 3a, 3b are calculated as 1458.21177830 (M), 2916.44667842 (D); 1257.245099 (M), 2514.513039 (D) a.u. respectively. The binding energy of dimer is computed as the difference between the calculated total energy of the dimer and the energies of the two isolated monomers. Thus, the binding energy of dimer is calculated as 43.26, 42.52 kJ/mol after correction in energy due to basis set superposition error (BSSE) [34]. 1

H NMR and

13

C NMR spectroscopy

The geometry of the title compound, together with that of tetramethylsilane (TMS) is fully optimized. 1H NMR chemical shifts

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Fig. 1. Optimized geometry for the ground state lower energy conformer of 3a, b.

are calculated with GIAO approach at B3LYP/6-31G(d,p) method [35]. The experimental 1H NMR spectra of 3a, b in DMSO-d6 are given in Fig. 3x, y, respectively. The calculated and experimental 1 H NMR chemical shifts of 3a, b in DMSO-d6 is given in Table 1. In the 1H NMR spectra of 3a, b a quartet and a triplet chemical shift designate presence of the ester ACH2, ACH3 group in all the molecules. The observed chemical shifts as a singlet at 8.199, 8.190 ppm indicate hydrazone linkage (CH@NANHA) in these molecules. In 3a, b, the down field chemical shift of pyrrole NH at 11.756, 11.007 ppm are responsible for intermolecular hydrogen bonding N1AH30  O84/N74AH80  O20, N1AH28  O60/N61AH64   O15, respectively. In order to compare the chemical shifts, correlation graph between the experimental and calculated 1H NMR chemical shifts is shown in Supplementary Fig. S1. The correlation coefficients (R2 = 0.91, 0.97) for 3a, b show that experimental 1H NMR data is consistent with the calculated data from optimized structure of probed molecules. The calculated and experimental 13C NMR chemical shifts of 3a, b in DMSO-d6 is given in Table 2. Additional support for molecular structures of 3a, b are provided by their 13C NMR spectra, in which chemical shifts of the C7 carbon atom at 132.15, 134.84 ppm for ACH@NA confirm the hydrazone character of these molecules. The experimental 13C NMR spectra of 3a, b in DMSO-d6 are given in Fig. 4x, y, respectively. In order to compare the chemical shifts, correlation graph between the experimental and calculated 13C NMR chemical shift is shown in Supplementary Fig. S2. The correlation coefficients (R2 = 0.97, 0.99) for 3a, b show that experimental

13

C NMR chemical shifts are in good agreement with the calculated chemical shifts. Electronic absorption (UV–Visible) spectroscopy The nature of the excitations in the observed UV–Visible spectrum of the title compound has been studied by the time dependent density functional theory (TD-DFT). The calculated and experimental electronic excitations of high oscillatory strength are listed in Table 3. The experimental UV–Visible spectra of 3a, b are shown in Fig. 5x, y, respectively. Frontier molecular orbitals i.e. the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are very popular quantum chemical parameters. They determine the molecular reactivity and ability of a molecule to absorb light. The vicinal orbitals of HOMO and LUMO play the same role of electron donor and electron acceptor, respectively. The HOMO–LUMO energy gap is an important reactivity index. The HOMO–LUMO energy gap of 2.69, 4.52 eV for 3a, b reflects the chemical reactivity of these molecules. The molecular orbital plots for high oscillator strength electronic excitations in 3a, b are shown in Supplementary Fig. 3x, y, respectively. A combined experimental and theoretical UV–Visible spectrum analysis of 3a indicates that the first observed electronic excitation at kmax = 237 nm corresponds to the aggregate of three electronic excitations calculated at k = 253.5 nm, f = 0.37; k = 260.5 nm, f = 0.18; k = 278.2 nm, f = 0.24. The second observed

P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339

329

Fig. 2. (x, y) Optimized geometry for dimer of ground state lower energy conformer of 3a, b.

k at 320 nm is in agreement with the calculated kmax = 349.2 nm, f = 0.58. For 3b, the first observed k = 226 nm corresponds to the aggregate of two electronic excitations calculated at k = 238.4 nm, f = 0.42; k = 260.3 nm, f = 0.49. The second observed kmax at 293 nm agrees well with the calculated electronic excitations

at kmax = 301.1 nm, f = 0.85. Therefore, the observed kmax is slightly blue shifted compared with the calculated kmax. On the basis of molecular orbital coefficients and molecular orbital plots, nature of all the electronic excitations in both molecules is assigned as p ? p⁄.

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Fig. 3. (x, y) The experimental 1H NMR spectra of 3a, b in DMSO-d6 solvent.

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P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339 Table 1 Calculated and experimental 1H NMR chemical shifts of 3a, b using B3LYP/6-31G(d,p) in DMSO-d6 at 25 °C. 3a

3b

Assignment

Atom no.

dcalcd.

dexp.

Atom no.

dcalcd.

dexp.

H30 H31 H32 H33 H34

9.168 2.201 2.568 2.724 8.149

11.756 2.248

H28 H29 H30 H31 H32

8.621 2.551 2.575 2.220 7.879

11.007 2.267

(s, 1H, pyrrole-NH) (s, 3H, pyrrole-CH3)

8.190

H35 H36 H37 H38

3.029 2.099 2.131 9.169

2.205

H33 H34 H49 H35

2.093 2.962 2.095 8.104

2.330

(s, 1H, Schiff base ACH@N) (s, 3H, pyrrole-CH3)

H39 H40 H41 H42 H43 H44 H45 H46 – –

9.132 9.571 9.520 4.309 4.308 1.216 1.462 1.465 – –

– –

H44/48 – H45–47 H38 H39 H40 H41 H42 H43 H36

8.775/6.941 – 7.190–7.470 4.274 4.241 1.221 1.461 1.454 9.920 3.560

–

–

–

H37

2.662

Table 2 Calculated and experimental

13

8.199

11.699 8.956–8.979 9.099 8.500 4.210–4.279 1.279–1.325

10.070 7.978–8.003 – 7.006–7.605 4.167–4.238

(s, 1H, ACH@NANHA) (d, 1H)/(d, 2H) ArAH (s, 1H, ArACH) (s, 1H)/(m, 3H) ArAH (q, J = 6.904, 2H, ester CH2)

1.240–1.286

(t, J = 6.902, 3H, ester CH3)

11.592 3.642

(s, 2H, COACH2ACO)

(s, 1H, ANHAC6H5)

C NMR chemical shifts of 3a, b using B3LYP/6-31G(d,p) in DMSO-d6 at 25 °C.

Atom no.

dcalcd.

dexp.

Assignment

Atom no.

dcalcd.

dexp.

Assignment

C2 C3 C4 C5 C6 C7 C8 C9

118.345 127.647 117.866 135.25 19.5855 139.973 13.4345 158.748

117.05 122.96 116.04 128.7 17.03 132.15 14.9 150.74

Pyrrole ring Pyrrole ring Pyrrole ring Pyrrole ring Pyrrole-CH3 Schiff base Pyrrole-CH3

C2 C3 C4 C5 C6 C7 C8 C9

118.015 127.798 117.628 135.022 19.6255 139.123 13.3725 158.732

117.52 121.9 115.02 127.95 17.86 134.84 14.23 148.04

Pyrrole ring Pyrrole ring Pyrrole ring Pyrrole ring Pyrrole-CH3 Schiff base Pyrrole-CH3 Ester ˜C@O

C12

154.508

148.66

C12

160.017

148.9

ANHAC@O

C14

137.418

130.04

ANHAC@O Benzene ring

C14

46.703

44.2

C15 C16 C17

125.874 148.095 121.594

120.58 139.38 119.64

Benzene ring Benzene ring Benzene ring

C17 C18 C19

63.986 17.173 159.108

52.8 15.68 148.46

COACH2A Ester-CH2 Ester-CH3

C18 C19 C22 C23

148.992 130.842 63.8705 17.0455

140.05 125.04 53.07 15.94

Benzene ring Benzene ring Ester-CH2 Ester-CH3

C22 C23 C24 C25 C26 C27

137.457 115.335 126.675 120.208 126.235 115.127

130.12 108.22 110.88 110.24 110.48 108.06

Ester ˜C@O

Natural bond orbitals (NBO) analysis Natural bond orbital (NBO) analysis is an important tool for studying hybridization, covalency effects, hydrogen-bonding and van der Waals interactions [36–39]. In 3a, b, the interactions p(C2AC3) ? p⁄(C4AC5), p(C4AC5) ? p⁄(C2AC3) are responsible for the conjugation of respective p-bonds in pyrrole ring due to the high electron density at conjugated p bonds (1.677–1.771) and low electron density at p⁄ bonds (0.379–0.422) and stabilized the molecules with energy 64.85, 103.05 kJ/mol, respectively. The interaction n1(N1) ? p⁄(C2AC3)/p⁄(C4AC5) shows that loan pair of pyrrole N atom take part in electron delocalization within ring and stabilized the molecules with maximum energy in the region 128.83–205.02 kJ/mol. In same manner, the p ? p⁄ interactions of benzene ring in 3a, b designate the conjugation of respective p-bonds within ring and stabilized the molecules in a broad region 67.80–92.17 kJ/mol, due to presence of the different substituent at benzene ring. In 3a, the interactions p(C16AC17) ? p⁄(N24AO25), p(C18AC19) ? p⁄(N27AO28) are stabilized the molecule to a

ANHAC@O Benzene ring Benzene ring Benzene ring Benzene ring Benzene ring Benzene ring

greater extent 96.68 kJ/mol, due to presence of the NO2 group. It is to be noticed that the charge transfer interactions are formed by the orbital overlap between bonding (p) and antibonding (p⁄) orbitals, which results in intramolecular charge transfer (ICT) causing stabilization of the system. The movement of p-electron cloud from donor to acceptor i.e. intramolecular charge transfer (ICT) can make the molecules more polarized, which must be responsible for the NLO properties of molecules. Therefore, 3a, b, may be used for non-linear optical materials. In 3a, b, the primary hyperconjugative interactions n1(O21) ? r⁄(C8AH35), n1(O16) ? r⁄(C8AH34) are responsible for intramolecular hydrogen bonding as C8AH35  O21, C8AH34  O16, respectively. The secondary hyperconjugative interactions r ? r⁄ associated with pyrrole and benzene ring are stabilized the molecules with energy in the region 13.97–25.90, 10.96– 19.41 kJ/mol, respectively. The presence of nitro group in 3a stabilized the molecule to a greater extent 680.20, 693.60 kJ/mol due to the interactions n2(O26) ? p⁄(N24AO25), n2(O29) ? p⁄ (N27AO28), respectively. In 3b, the interactions n1(O13) ? r⁄

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Fig. 4. (x, y) The experimental

13

C NMR spectra of 3a, b in DMSO-d6 solvent.

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Table 3 Comparison between calculated and experimental electronic excitations for 3a, b: E (eV), oscillatory strength (f), kmax (nm) using TD-DFT/B3LYP/6-31G(d,p) in DMSO at 25 °C.

3a

3b

Excitations

E

Oscillator strength (f)

kmax calcd.

kmax exp.

Assignment

97 ? 107, H  8 ? L + 1 105 ? 110, H ? L + 4 105 ? 109, H ? L + 3 105 ? 108, H ? L + 2

4.88 4.75 4.45 3.55

0.37 0.18 0.24 0.58

253.5 260.5 278.2 349.2

237

p ? p⁄

320

p ? p⁄

96 ? 100, H  2 ? L + 1 96 ? 99, H  2 ? L 98 ? 100, H ? L + 1 98 ? 99, H ? L

5.20 4.76

0.42 0.49

238.4 260.3

226

4.11

0.85

301.1

293

p(C26AC27) ? p⁄(C7AN10) p(C26AC27) ? p⁄(C9AO15) p(C24AC25) ? p⁄(C7AN10) p(C24AC25) ? p⁄(C9AO15)

intermolecular interactions n1(O84)/n2(O84) ? r⁄(N1AH30), n1(O60)/ n2(O60) ? r⁄(N1AH28) whereas, the blue shift hydrogen bonding C6AH31  O84, C6AH31  O60 due to the interactions n1(O84)/n2(O84) ? r⁄(C6AH31), n1(O60)/n2(O60) ? r⁄(C6AH31), respectively. Selected Lewis orbitals (occupied bond or lone pair) of 3a, b with their NBO hybrid orbitals are listed in Supplementary Table S5. The NBO hybrid orbitals analysis shows that all the CAN bond orbitals are polarized towards the nitrogen atom (ED = 59.44–62.96% at N), whereas CAO/NAO bond orbitals towards oxygen atom (ED = 51.35–68.21% at O). The electron density distribution (occupancy) around the lone pair also influences the polarity of the compound. Therefore, they consist with the maximum electron density on the oxygen and nitrogen atoms, which is responsible for the polarity of molecule. Vibrational analysis The theoretical (selected) and experimental vibrational modes of 3a, b, and their approximate assignments are given in Table 4. Comparison between experimental and theoretical IR spectra in the region 4000–400 cm1 is shown in Fig. 6x, y. The calculated vibrational wavenumbers are higher than their experimental values for the majority of the normal modes. Two factors may be responsible for the discrepancies between the experimental and computed wavenumbers. The first is caused by the environment (gas and solid phase) and the second is due to the fact that the experimental values are an anharmonic wavenumbers while the calculated values are harmonic ones. Therefore, mcalcd are scaled down using scaling factor 0.9608 [40], to discard the anharmonicity present in real system.

Fig. 5. (x, y) The experimental UV–Visible spectra of 3a, b.

(N21AH43), n1(O20) ? r⁄(C23AH44) are responsible for intramolecular hydrogen bonding as N21AH43  O13, C23AH44  O20, respectively. Second order perturbation theory analysis of the Fock matrix in NBO basis for for various intra- and intermolecular interactions in dimer of 3a, b are given in Supplementary Table S4. In dimer of 3a, b, the primary hyperconjugative interactions n1(O20)/n2(O20) ? r⁄(N74AH80), n1(O15)/n2(O15) ? r⁄(N61AH64) from monomer unit (1) to unit (2) confirm presence of the classical hydrogen bonding N74AH80  O20, N61AH64  O15 and stabilized the molecule up to 41.47 kJ/mol. Another weak intermolecular interactions n1(O20)/n2(O20) ? r⁄(C75AH81), n1(O15)/ n2(O15) ? r⁄(C67AH74) confirm presence of the blue shift hydrogen bonding C75AH81  O20, C67AH74  O15, respectively. In same way, for 3a, b the conventional hydrogen bonding N1AH30  O84, N1AH28  O60 can be explained due to the

NAH vibrations In the experimental FT-IR spectra of 3a, b, the NAH stretches of pyrrole (mN1AH30/28) are observed at 3276, 3268 cm1, whereas these are calculated at 3336–7 cm1 in dimer and 3498–9 cm1 in monomer. The observed wavenumbers at 3276, 3268 cm1 are in good agreement with the mcalcd in dimer than monomer and also correlate with the earlier reported strong absorption band at 3358 cm1 for hydrogen bonded dimer of pyrrole-2-carboxylic acid recorded in solid state using KBr pellet, but it deviates to the reported free mNH band at higher wavenumber 3465 cm1, recorded in solution phase [41]. Therefore, solid state spectra of 3a, b attribute to the vibration of hydrogen bonded NAH group. In dimer, the stretching wavenumber of hydrogen bond donor (NAH) is red-shifted (i.e. the elongation of NAH bond) due to its conventional nature than the hydrogen bond free NAH group in monomer. In 3a, b, the observed NAH wagging modes of pyrrole (xN1AH30/28) at 774, 779 cm1 correspond to the mcalcd at 795– 6 cm1. The observed CANAH bending vibrations of pyrrole at 1280, 1272 cm1 agree well with the mcalcd at 1269–70 cm1. In 3a, b, the observed wavenumbers at 3425, 3440 cm1 designate to the NAH stretches of C@NANAH part of molecule. The observed

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Table 4 Theoretical (dimer) and experimental vibrational wavenumbers of 3a, b at B3LYP/631G(d,p) level and their assignments: Wavenumbers ðV=cm1 Þ, Intensity (km mol1). V calcd.

V exp.

V calcd.

V exp.

Assignment PED

3369

3425

3369

3440

3336 –

3276 –

3337 3318

3268 –

3143 – 3010 2986 2945 2919 1716

3097 – 2988 – 2927 2877 1782

3080 3067 3010 2986 2945 2919 1693

3093 3043 2981 – 2923 2870 1674

1657 1616 1596

1658 1613 1574

1657 1620 1590

1644 1605 1560

1568 1544 1473 1472 1440 1373 –

1543 1502 1464 – 1432 1378 –

– 1547 1481 1472 1440 1373 1341

– 1512 1444 – 1418 1367 1319

mNAH ACH@NANH mNAH-pyrrole mNAH ANHACO mCAH-benzene mCAH-benzene mas-CH ester Me mas-CH ester CH2 ms-CH ester CH2 m-CH pyrrole Me mC@O ACH@NANHACO mC@O ester carbonyl mC@N -Schiff base [mCAC R1 + dANH ANHACO] masANO2 mC@C pyrrole [mCAC R1 + dCAHACAR1]

1339 1272 1268

1344 – 1280

– 1291 1269

– – 1272

1244 1206 1137

1233 1195 1102

1243 1194 1125

1226 1180 1127

1098 1089

– 1076

1098 1087

– 1091

1081 1006 976 897 839 795 737

– 949 918 887 843 774 730

1072 1006 973 – 836 796 744

– 945 932 – 822 779 755

700 642 613 551 522

654 626 601 566 527

678 632 616 558 510

671 630 609 557 500

482

483

468

468

dsc-CH2 ester das-Me1 ds-Me1

x-CH2 [COACH2ACO] ms-NO2 x-ester CH2 dCNH pyrrole + m(O@CAO) mCAN O@CAN [dipAR1 + mCAN O@CAN] t-CH2 [COACH2ACO + ester] q-Me

m(CAOAC) ester d-CHC benzene

mCAC ester (d-OCN) + (d-NNC) d-NO2 [d-COC ester + doop-R1] x-NH pyrrole

x-NH [˜CONH] x-CH [R1] + R1-puckering d-CCC pyrrole + d-OCO ester doop-C@O [˜CONH carbonyl] doop-CAH [R1]

x-NH [C@NANAH] x-NH [C@NANAH]

ms – symmetric stretching, mas – asymmetric stretching, dsc – scissoring, x – wagging, t – twisting, d – deformation, dip – in plane deformation, doop – out of plane deformation, R1 – benzene.

respectively [43]. The xACH2 of COACH2ACO is observed at 1319 cm1, whereas this is assigned at 1341 cm1 in theoretical IR spectrum [43]. The observed wavenumbers at 1102, 1127 cm1 assign to the twisting mode of CH2 group. According to the Internal coordinate system recommended by Pulay et al. [42], CH3 group associate with different vibrational modes namely: symmetric stretch (ms), asymmetric stretch (mas), symmetric deformation (ds), asymmetric deformation (das) and rocking (q). In 3a, b, the observed masCH3 at 2988, 2981 cm1 correspond to the mcalcd at 3010 cm1 and also matches well with the reported band in the region 2985 ± 25, for asymmetric CAH stretches of CH3 [43]. In 3a, b, the observed bands at 1432, 1418 cm1 display the das deformation modes, whereas bands at 1378, 1367 cm1 to the ds deformation modes of methyl groups, respectively. The CAH stretches (ArAmCAH), ‘in-plane’ (dipAR1) and ‘out-of-plane’ (doopAR1) bending vibrations in substituted benzenes absorb in the regions 3100–3000, 1300–1000, 900–675 cm1, respectively [44]. In 3a, b, the observed bands at 3097, 3093 cm1 assign to the ArAmCH stretching vibrations. The observed wavenumbers at 1195, 1180; 843, 822 cm1 assign to the dipACH, doopACH bending vibrations of benzene ring, respectively. A combination band of xACH and ring puckering vibration (a tortional mode) of benzene at 654, 671 cm1 corresponds to the mcalcd at 700, 678 cm1. C@O, CAO vibrations In the experimental FT-IR spectra, ester carbonyl stretches (mC@O) for 3a, b are observed at 1658, 1644 cm1, whereas these are calculated at same wavenumber 1657 cm1 in dimer and 1690 cm1 in monomer. The downshifted observed mC@O at 1658, 1644 cm1 also correspond to the earlier reported wavenumber at 1665 cm1 for dimer of syn-pyrrole-2-carboxylic acid [41]. Therefore, the downshifting in the mC@O stretching mode in 3a, b confirms the involvement of C@O group in intermolecular hydrogen bonding. In dimer, the stretching wavenumber of hydrogen bond acceptor (C@O) is red-shifted due to its conventional nature than the hydrogen bond free C@O group in monomer. In 3a, b, the observed wavenumber at 1782, 1674 cm1 demonstrate to the mC@O of ACH@NANHACO part of molecule, respectively. The observed symmetric and asymmetric stretching vibrations of ester CAO at 1076, 1091; 1280, 1272 cm1 agree with the mcalcd at 1088– 7; 1268–9 cm1, respectively. In 3a, b, the observed wavenumber at 843, 822 cm1 assign to the deformation mode of ester CAOAC, respectively.

xNAH of C@NANAH at 527, 500 cm1 well correspond to the mcalcd at 522, 510 cm1. CAH vibrations Three methyl groups are present in the molecule. Two of them are directly attached to the C5, C3 carbon atoms of pyrrole ring and one with the CH2 of ester group. The pyrrole and benzene ring are abbreviated as R and R1, respectively. According to the Internal coordinate system recommended by Pulay et al. [42], CH2 group associate with six types of vibrational frequencies namely: symmetric stretch (ms), asymmetric stretch (mas), scissoring (dsc), rocking (q), wagging (x) and twisting (t). The dsc and q deformations belong to polarized ‘in-plane’ vibration, whereas x and t deformations belong to depolarized ‘out-of-plane’ vibration. In 3a, b, the calculated weak band at 2986 cm1 designates to the masCH2 and matches well with the reported band in literature in the region 3000 ± 50 [43]. The observed msCH2 at 2927, 2923 cm1 correspond to the mcalcd at 2945 cm1 and also matches well with reported band in literature in the region 2965 ± 30 cm1, for symmetric CAH stretches of CH2 [43]. The (dsc) and (x) deformation modes for ester CH2 assigned at 1472, 1272–1291 cm1 match well with the reported bands in the region 1455 ± 55, 1350 ± 85 cm1,

C@N, CAN and CAC vibrations For 3a, b, Schiff base tC@N modes assigned at 1616, 1620 cm1 match well the observed wavenumbers at 1613, 1605 cm1, experimentally. The presence of the tC@N bands in 3a, b confirm hydrazone linkage in the investigated molecules. The calculated bands for tC@N also match with the reported band at 1602 cm1 [45]. The observed wavenumber at 1233, 1226 cm1 assign to the mCAN stretches and in agreement with the reported band in the region 1275 ± 55 cm1 [46]. The CAC stretches in pyrrole ring are observed at 1502, 1512 cm1, whereas they are calculated at 1544, 1547 cm1. The observed dCACAC associated with pyrrole ring at 626, 630 cm1 agree with the mcalcd at 642, 632 cm1, respectively. In aromatic hydrocarbons, the skeletal vibrations involving carbonAcarbon stretching within the ring absorb in the regions 1600–1585 and 1500–1400 cm1. The DFT modes at 1596, 1590 cm1 assign to the mCAC stretches in R1 and correspond to the observed band at 1574, 1560 cm1, respectively. The observed bands at 1464, 1444 cm1 demonstrate to a combination band of mCAC and dCAHAC associated with ring R1. In ring R1, DFT modes for doopACAC are observed at 566, 557 cm1 and also match well with the reported band at 600–420 cm1 [44].

P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339

335

Fig. 6. (x, y) The experimental and theoretical (monomer, dimer) IR spectra of 3a, b.

N@O vibrations The molecule under investigation 3a possesses two nitro groups. The nitro groups show two types of stretching vibrations as asymmetric (mas) and symmetric (ms). The mas stretches are always observed at higher wavenumber than ms stretches. In 3a, the mas and ms stretch of nitro groups calculated at 1568, 1339 cm1 are in agreement with the observed wavenumbers at 1543, 1344 cm1, respectively. The mas and ms stretching vibrations of nitro group are also reported in literature at 1600, 1319 cm1, respectively [46]. The calculated d-NO2 at 897 cm1 is observed at same wavenumber in the experimental FT-IR spectrum.

hydrogen bond energy (E). Espinosa proposed proportionality between hydrogen bond energy (E) and potential energy density (VBCP) at H  N/O contact as E = 1/2 (VBCP) [49]. According to this equation, In 3a hydrogen bond energy of N1AH30  O84, C8AH35  O21, C75AH81  O20 are calculated as 25.64, 13.84, 6.42 kJ/mol, whereas in 3b hydrogen bond energy of N1AH28  O60, C8AH34  O6, C6AH31  O60, N21AH43  O13, C23AH44   O20 are calculated as 25.61, 13.73, 6.40, 30.46, 17.69, respectively. In 3a, b, the presence of bond critical point (BCP) at C6  N10 contact designates presence of the intermolecular interaction.

Quantum theory of atoms in molecules (QTAIM) analysis

Chemical reactivity

Molecular graphs of 3a, b using AIM program at B3LYP/631G(d,p) level are shown in Supplementary Fig. S4x, y. Topological as well as geometrical parameters for bonds of interacting atoms in 3a, b are given in Supplementary Tables S6 and S7, respectively. For all the intra and intermolecular interactions NAH  O/CAH  O electron density (qH  A) and its Laplacian (r2qBCP) follows the Koch and Popelier criteria and the distance between interacting atoms (dH  O = 1.90–2.58 Å) is less than the sum of van der Waals radii of these atoms (rH + rO = 2.72). Therefore, these interactions are hydrogen bonds. In 3a, b, all the hydrogen bonds are weak due to (r2qBCP) > 0 and HBCP > 0, whereas in 3b intramolecular hydrogen bond N21AH43  O13 is medium due to (r2qBCP) > 0 and HBCP < 0. In this article, QTAIM theory is used to estimate

The chemical reactivity of molecule is described in three ways as: (i) Molar refractivity (MR) (ii) Global and local electronic reactivity descriptors. Molar refractivity (MR) Molar refractivity (MR) is an important property used in quantitative structure property relationship (QSPR). It is directly related to the refractive index, molecular weight and density of steric bulk and responsible for the lipophilicity and binding property of investigated system. It can be calculated by the Lorentz–Lorentz equation [47–49] and defined as:

  MR ¼ ðn2  1Þðn2 þ 2Þ  ðMW=qÞ ¼ 1:333 pNa0

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where n – refractive index, MW – molecular weight, q – density, (MW/q) – molar volume, N – Avogadro Number, a0 – polarizability of molecular system. This equation holds for both liquid and solid state of system. Molar refractivity is related to the London dispersive forces that act in the drug–receptor interaction. Using this equation, the molar refractivity (MR) for 3a, b are calculated as 104.4, 101.9 esu, respectively, which responsible for binding property of aroylhydrazone molecules for treatment of different diseases. Molar refractivity based binding property of 4-Quinolinyl and 9-Acrydinylhydrazones as potent antimalarial agents active against C-Q resistant clone K1 Plasmodium falciparum strain is also well reported in literature [50].

Table 6 Selected electrophilic reactivity descriptors (fk+, sk+, xk+) for reactant 1 and nucleophilic reactivity descriptors (fk, sk, xk) for reactants 2a, b using Hirshfeld charges. 1

fk+

sk +

xk+

2a

fk

sk 

xk

C7 C10

0.1479 0.0921

0.0287 0.0179

0.3702 0.2305

N9 N10

0.1066 0.1312

0.0246 0.0302

0.7374 0.9071

2b N1 N23

0.0288 0.0361

0.0047 0.0058

0.0359 0.0450

fk+, fk (in e); sk+, sk (in eV1) and xk+, xk (in eV).

xfk+, xk = xfk, where, + and  sign show nucleophilic, electroElectronic reactivity descriptors Global reactivity descriptors. Global chemical reactivity descriptors such as electronegativity (v) = 1/2(eLUMO + eHOMO), chemical potential (l) = 1/2 (eLUMO + eHOMO), global hardness (g) = 1/2 (eLUMO – eHOMO), global softness (S) = 1/2g and electrophilicity index (x) = l2/2g are highly successful in predicting global reactivity trends [51–60]. According to Parr et al., electrophilicity index (x) is a global reactivity index similar to the chemical hardness and chemical potential. This is positive and definite quantity and measures the stabilization in energy when the system acquires an additional electronic charge (DN) from the environment. The energies of frontier molecular orbitals (eHOMO, eLUMO), energy gap (eLUMO – eHOMO), electronegativity (v), chemical potential (l), global hardness (g), global softness (S), global electrophilicity index (x) for 1; 2a, b; 3a, b and ECT for reactant systems as [1 M 2a], [1 M 2b] are listed in Table 5. The global elecrophilicity index (x = 7.71, 2.66 eV) for 3a, b shows that 3a behaves as strong electrophiles than 3b. Electrophilic charge transfer (ECT) = (DNmax)A – (DNmax)B [60] is defined as the difference between the DNmax values of interacting molecules A and B. If we consider two molecules A and B approach to each other (i) if ECT > 0, charge flow from B to A (ii) if ECT < 0, charge flow from A to B. ECT is calculated as 0.31, 0.49 for reactant systems [1 M 2a], [1 M 2b], respectively i.e. ECT > 0, which indicates that charge flows from 2a, b to 1. Therefore, 1 acts as global electrophile and 2a, b as global nucleophile. Local reactivity descriptors. The site selectivity of a chemical system cannot be studied using the global reactivity descriptors. For this purpose, appropriate local reactivity descriptors as Fukui function to describe the reactivity of an atom in a molecule are needed to be defined. The local reactivity descriptors [51–60] such as Fukui functions fk+(r), fk(r) are calculated using the following equations as: fk+(r) = [qk(N + 1) – qk(N)], for nucleophilic attack; fk(r) = [qk(N) – qk(N  1)], for electrophilic attack, where, q is the gross charge of atom k in the molecule and N, N + 1, N  1 are electron systems containing neutral, anion, cation form of molecule, respectively. Using Fukui functions, other local reactivity descriptors as local softnesses (sk+, sk) and electrophilicity indices (xk+, xk) are calculated using following equations as: sk+ = Sfk+, sk = Sfk; xk+ =

philic attack, respectively. Selected electrophilic reactivity descriptors (fk+, sk+, xk+) for reactant (1) and nucleophilic reactivity descriptors (fk, sk, xk) for reactants 2a, b using Hirshfeld charges are given in Table 6. The maximum values of local electrophilic reactivity descriptors (fk+, sk+, xk+) at aldehyde carbon C7 of reactant 1 indicates that this is the most electrophilic site. The nucleophilic reactivity descriptors (fk, sk, xk) of reactant 2a, b shows that N atom of NH2 (N10/N23) is the most nucleophilic site. Therefore, the nucleophilic attack of N10 site for 2a and N23 for 2b at the most electrophilic site C7 of reactant 1 confirms formation of product molecules or Schiff base linkage (C7@N10) in aroylhydrazones 3a, b. Selected reactivity descriptors as Fukui functions (fk+, fk), local softnesses (sk+, sk), local electrophilicity indices (xk+, xk) for 3a, b using Hirshfeld charges are given in Table 7. In product molecules 3a, b the maximum values of the electrophilic reactivity descriptors (fk+, sk+, xk+) at Schiff base carbon (C7) indicate that this site is more prone to nucleophilic attack. Therefore, electrophilic reactivity descriptors of 3a, b favor the formation of new heterocyclic compounds such as oxadiazoline, thiazolidinones and azetidinones etc. by attack of nucleophilic part of the dipolar reagent on the C7 site of C7@N10 bond. In same way, the maximum values of the nucleophilic reactivity descriptors (fk, sk, xk) at N11, N21 indicate that this site is more prone to electrophilic attack for 3a, b, respectively. Static dipole moment (l0), mean polarizability (|a0|), anisotropy of polarizability (Da) and first hyperpolarizability (b0) Theoretical calculation provides another method to investigate substantial characters of materials. Hyperpolarizability is difficult task to measure directly; computational calculation is analternate choice and provides another method to investigate extensive properties of materials. Polarizabilities and hyperpolarizabilities are described to response of a system in the presence of an applied electric field [61]. They determine the strength of molecular interactions (long-range intermolecular induction, dispersion forces, etc.), cross sections of different scattering and collision processes, as well as the non-linear optical (NLO) properties of the system [62,63]. In order to investigate the relationship between molecular structure and NLO response, first hyperpolarizability (b0) of this

Table 5 Calculated (eH, eL), energy band gap (eL – eH), electronegativity (v), chemical potential (l), global hardness (g), global softness (S) and global electrophilicity index (x) for 1; 2a, b; 3a, b and Electrophilic charge transfer (ECT) for reactant systems [1 M 2a], [1 M 2b].

1 2a 3a 2b 3b

eH

eL

(eL – eH)

v = l

g

S

x

ECT

6.1609 7.6391 5.9022 5.8366 5.7332

1.0163 3.3064 3.2120 0.3074 1.2090

5.1446 4.3326 2.6901 6.1441 4.5242

3.5886 5.4728 4.5571 2.7645 3.4711

2.5723 2.1663 1.3450 3.0720 2.2621

0.1943 0.2308 0.3717 0.1627 0.2210

2.5032 6.9130 7.7198 1.2439 2.6631

(0.3115)[1M2a]

H-HOMO, L-LUMO; eH, eL, (eL – eH), v, l, g, x (in eV) and S (in eV1).

(0.4952)[1M2b]

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P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339 Table 7 Selected electrophilic (fk+, sk+, xk+) and nucleophilic (fk, sk, xk) reactivity descriptors for products 3a, b using Hirshfeld charges. Sites

fk+

sk +

xk+

3a

C7 C9 C12

0.0171 0.0043 0.0012

0.0063 0.0016 0.0004

0.1323 0.0335 0.0097

3b

C7 C9 C12 C19

0.1284 0.0440 0.0581 0.0119

0.0283 0.0097 0.0128 0.0026

0.3420 0.1172 0.1547 0.0317

Sites

fk

sk 

xk

3a

N1 N11

0.0532 0.0794

0.0198 0.0295

0.4112 0.6132

3b

N1 N11 N21

0.0352 0.0445 0.0492

0.0077 0.0098 0.0108

0.0939 0.1185 0.1312

fk+, fk (in e); sk+, sk (in eV1) and xk+, xk (in eV).

Table 8 Calculated dipole moment (l0), polarizability (|a0|), anisotropy of polarizability (Da), first hyperpolarizability (b0) and their components for 3a, b.

lx ly lz l0 axx ayy azz |a0| Da

3a

3b

5.92 2.37 0.81 6.43 461.16 260.10 116.98 41.40 126.42

5.11 1.17 0.53 5.27 429.36 250.92 137.20 40.38 116.51

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz b0

3a

3b

5286.76 774.76 231.17 316.21 347.38 79.20 59.91 30.25 23.58 17.44 48.96

331.73 320.33 127.48 130.52 142.32 36.24 48.21 1.06 23.11 14.91 4.50

l0 in Debye; |a0| and Da in 1024 esu; b0 in 1030 esu.

novel molecular system, and related properties (|a0| and Da) are calculated using B3LYP/6-31G(d,p), based on the finite-field approach and their calculated values are given in Table 8. In the presence of an applied electric field, the energy of a system is a function of the electric field. First hyperpolarizability is a third rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 3D-matrix can be reduced to 10 components due to the Kleinman symmetry [64]. It can be given in the lower tetrahedral format. Total static dipole moment (l0), mean polarizability (|a0|), anisotropy of polarizability (Da) and first hyperpolarizability (b0), using x, y, z components are defined as [65].



l0 ¼ l2x þ l2y þ l2z

1=2

  ja0 j ¼ 1=3 axx þ ayy þ azz h i1=2 2  2 Da ¼ 21=2 axx  ayy þ ayy  azz þ ðazz  axx Þ2 þ 6 a2xx b0 ¼

h

bxxx þ bxyy þ bxzz

2

 2  2 i1=2 þ byyy þ bxxy þ byzz þ bzzz þ bxxz þ byyz

Large value of particular component of the polarizability and hyperpolarizability indicate a substantial delocalization of charge in these directions. Since the value of the polarizability (|a0|), first hyperpolarizability (b0) of Gaussian 09 output are reported in atomic unit (a.u.) and these values are converted into electrostatic unit (esu) using converting factors as (for a0: 1 a.u. = 0.1482  1024 esu; for b0: 1 a.u = 0.008639  1030 esu). The first hyperpolarizabilities (b0) of the title molecules (3a, b) are calculated as 48.96, 4.50  1030 esu, respectively. In this study, p-Nitroaniline (p-NA) is chosen as a reference molecule because there were no experimental values for the title compound. The p-NA is one of the prototypical molecules used in the study of the NLO properties of molecular systems (for p-NA, b = 8.5  1030 esu) [66]. The 3a has high first hyperpolarizability

due to presence of two strong charge acceptor nitro group. In case of 3b the acceptor side is weak and intramolecular hydrogen bonding further alter its capacity, therefore has low first hyperpolarizability. Therefore, the investigated molecule (3a) will show good non-linear optical response than (3b) and can be used as non-linear optical (NLO) material. Conclusions In this study the detailed analysis of synthesized pyrrole aroylhydrazones 3a, b by spectroscopic and theoretical techniques has been presented. The calculated 1H NMR chemical shifts are in good agreement with the observed chemical shifts, experimentally. A combined experimental and theoretical UV–Visible spectral analysis indicates that observed kmax have blue shifts compared to the calculated kmax values. The molecular orbital coefficients and molecular orbital plots analysis suggest that nature of electronic excitations involved in both molecules 3a, b as p ? p⁄. The down field 1H NMR chemical shift, NBO interactions as n(O84) ? r⁄(N1AH30)/n(O60) ? r⁄(N1AH28) and vibrational red shift in both proton donor pyrrole NAH and proton acceptor ester carbonyl C@O show presence of intermolecular hydrogen bonding N1AH30  O84/N74AH80  O20, N1AH28  O60 N61AH64  O15, respectively. AIM calculation also confirms presence and strength of these hydrogen bonds due to existence of the bond critical point (BCP) at H  O contact. The high value of global elecrophilicity index (x = 7.71 eV) for 3a shows that this behaves as strong electrophile than 3b. In addition, theoretical results from local reactivity descriptors are in complete agreement with observed reactivity of hydrazones. The local electrophilic reactivity descriptors show that azomethine carbon (C7) of 3a, b is more reactive site for nucleophilic attack and used as precursor for the syntheses of new heterocyclic compounds as azetidinones, oxadiazolines and thiazolidinones. These compounds exhibits strong effective intramolecular charge transfer (ICT) due to movement of p-electron cloud from donor to acceptor i.e. shows high polarity and responsible for NLO properties of molecules. The large value of first hyperpolarizability (b0 = 48.96  1030 esu) of 3a show that this molecule can be used as attractive material for non-linear optical (NLO) applications. Quantum chemical calculations The quantum chemical calculations have been carried out using Gaussian 09 program package [67]. The optimization, 1H NMR chemical shifts, vibrational wavenumbers, global and local reactivity descriptors and first hyperpolarizability have been calculated at B3LYP functional and 6-31G (d,p) basis set. To estimate the thermodynamic parameters as enthalpy (H) and Gibbs free energy (G), the thermal corrections to these parameters are added to the calculated total energies. The 1H NMR chemical shifts are calculated using gauge including atomic orbital (GIAO) approach using

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IEFPCM model in appropriate solvent (DMSO). Time dependent density functional theory (TD-DFT) is used to find the various electronic excitations and their nature within molecule. The optimized geometrical parameters are used in the vibrational wavenumbers calculation to characterize all stationary points as minima and their harmonic vibrational wavenumbers are positive. Gauss-View program is used for visualization of optimized geometry of the molecules [68]. Experimental section All the chemicals were used of analytical grade. Ethyl 4-formyl3,5-dimetyl-1H-pyrrole-2-carboxylate was prepared by an earlier reported method [69]. Hydrazides (2a, b) were prepared by refluxing the equimolar reaction mixture of corresponding ester derivatives and hydrazine hydrate in methanol. The Mass spectra of 3a, b were recorded on JEOL-Acc TDF JMS-T100LC, Accu TOF mass spectrometer. The 1H NMR spectra were recorded in DMSO-d6 on Bruker DRX-300 spectrometer using TMS as an internal reference. The FT-IR spectra were recorded in KBr medium on a Brukerspectrometer. The UV–Visible absorption spectra (1  105 M in DMSO) were recorded on V-670 JASCO spectrophotometer. Synthesis of ethyl-4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5dimethyl-1H-pyrrole-2-carboxylate (3a) An equimolar solution of 3,5-dinitrobenzohydrazide (0.2317 g, 1.0251 mmol) and ethyl 4-formyl-3,5-dimetyl-1H-pyrrole-2-carboxylate (0.2000 g, 1.0251 mmol) in 20 ml methanol was stirred for 8 h at room temperature and precipitate was appeared. The precipitate was filtered off washed with methanol and dried in air, afforded 3a as yellow color solid. Yield: 0.175 g, 42.35%. m.p. – decomposed above 265 °C. MS (m/z): for C17H17N5O7 Calcd. 403.1128, Obs. 404.20 [M++1]. Anal. Calcd. for C17H17N5O7: C 50.60%, H 4.25%, N 17.36%; Obs.: C 50.64%, H 4.22%, N 17.38%. Synthesis of ethyl 3,5-dimethyl-4-[{2-phenylcarbamoyl-acetyl)hydrazonomethyl]-1H-pyrrole-2-carboxylate (3b) To the equimolar solution of 2-hydrazinocarbonyl-N-phenylacetamide (0.1978 g, 1.0251 mmol) and ethyl 4-formyl-3,5-dimetyl-1H-pyrrole-2-carboxylate (0.2000 g, 1.0251 mmol) in 25 ml methanol was added 0.01 ml of conc. HCl acid as catalyst. The reaction mixture was refluxed for 14 h and the precipitate was appeared. The precipitate was filtered off, washed with methanol and dried in air, afforded 3b as cream color solid. Yield: 68.52%, m.p.: decomposed above 220 °C, MS (m/z): for C19H22N4O4: Calc. 370.1641, Found 371.18 [M++1]. Anal. Calcd. for C19H22N4O4: C 61.59%, H 5.99%, N 15.143; obs.: C 61.62%, H 5.96%, N 15.16%. Acknowledgement The authors are thankful to the DST and CSIR for providing research fund and IIT Kanpur for spectral data. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.molstruc.2014. 12.045. References [1] R.M. Mohareb, R.A. Ibrahim, H.E. Moustafa, Open Org. Chem. J. 4 (2010) 8–14. [2] S. Rollas, S.G. Küçükgüzel, Molecules 12 (2007) 1910–1939.

[3] F. Armbruster, U. Klingebiel, M. Noltemeyer, Z. Naturforsch. 61b (2006) 225– 236. [4] B. Tang, L. Zhang, J. Zhang, Z. Chen, Y. Wang, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 60 (2004) 2425–2431. [5] E. Kavlentis, Anal. Lett. 21 (1988) 689–697. [6] P.V. Chalapathi, B. Prathima, Y.S. Rao, K.J. Reddy, G.N. Ramesh, D.V.R. Reddy, A.V. Reddy, Res. J. Chem. Environ. 15 (2011) 579–585. [7] J.R. Dimmock, S.C. Vashishtha, J.P. Stables, Eur. J. Med. Chem. 35 (2000) 241– 248. [8] P. Melnyk, V. Leroux, C. Serghergert, P. Grellier, Bioorg. Med. Chem. Lett. 16 (2006) 31–35. [9] L. Savini, L. Chiasserini, V. Travagli, C. Pellerano, E. Novellino, S. Cosentino, M.B. Pisano, Eur. J. Med. Chem. 39 (2004) 113–122. [10] S. Rallas, N. Gulerman, H. Erdeniz, IL FARMACO 57 (2002) 171–174. [11] A. Gursoy, N. Terzioglu, G. Otuk, Eur. J. Med. Chem. 32 (1997) 753–757. [12] O.O. Ajani, C.A. Obafemi, O.C. Nwinyi, D.A. Akinpelu, Bioorg. Med. Chem. 18 (2010) 214–221. [13] L.W. Zheng, L.L. Wu, B.X. Zhao, W.L. Dong, Y.J. Miao, Bioorg. Med. Chem. 17 (2009) 1957–1962. [14] D.R. Richardson, P.V. Bernhardt, J. Biol. Inorg. Chem. 4 (1999) 266–273. [15] K.K. Bedia, V.O.E. Seda, K. Fatma, S. Nathaly, R. Sevim, A. Dimoglo, Eur. J. Med. Chem. 41 (2006) 1253–1261. [16] G. Darnell, D.R. Richardson, Blood 94 (1999) 781–792. [17] M. Yu, H. Lin, H. Lin, Ind. J. Chem. Sec. A 46 (2007) 1437–1439. [18] B. Szczesna, U. Lipkowska, Supramol. Chem. 13 (2001) 247–251. [19] Y.P. Wu, E. Rahm, R. Holze, Electrochim. Acta 47 (2002) 3491–3507. [20] M. Koh, T. Nakajima, R.N. Singh, Mol. Cryst. Liq. Cryst. 310 (1998) 341–346. [21] V.P. Gupta, P. Tandon, P. Rawat, R.N. Singh, A. Singh, Astron. Astrophys. 528 (2011) 129–134. [22] Y. Shirota, H. Kageyama, Chem. Rev. 107 (2007) 953–1010. [23] W. Blau, Phys. Technol. 18 (1987) 250–268. [24] R.F. Vogt, G. E Martin, V. Zenger, in: O.S. Wolfbeis (Ed.), Springer Series on Fluorescence, vol. 5, Springer, Berlin, 2008, pp. 4–31. [25] U.R. Genger, D. Pfeifer, K. Hoffmann, G. Flachenecker, A. Hoffman, C. Monte, in: O.S. Wolfbeis (Ed.), Springer Series on Fluorescence, vol. 5, Springer, Berlin, 2008, pp. 65–99. [26] Y. Gu, T. Kar, S. Scheiner, J. Am. Chem. Soc. 121 (1999) 9411–9422. [27] F.H. Allen, V.J. Hoy, J.A.K. Howard, V.R. Thalladi, G.R. Desiraju, C.C. Wilson, G.J. Mcintyre, J. Am. Chem. Soc. 119 (1997) 3477–3480. [28] D. Philp, J.M.A. Robinson, J. Chem. Soc. Perkin Trans. 2 (1998) 1643–1650. [29] E.-Y. Wei, Acta Cryst. E 68 (2012) o1304. [30] Q.-S. Zong, Acta Cryst. E 68 (2012) o1338. [31] C.T. Arrannja, M.R. Siva, A.M. Beja, A.F.P.V. Ferreira, A.J.F.N. Sobral, Acta Cryst. E 64 (2008) o1989. [32] M.G. Gardiner, R.C. Jones, S. Ng, J.A. Smith, Acta Cryst. E 63 (2007) o470. [33] M.C. Etter, Acc. Chem. Res. 23 (1990) 120–126. [34] S.F. Boys, F. Bernardi, Mol. Phys. 19 (1970) 553–566. [35] K. Wolinski, J.F. Hinton, J.F. Pulay, J. Am. Chem. Soc. 112 (1990) 8251–8260. [36] I.M. Snehalatha, C. Ravikumar, I.J. Hubert, N. Sekar, V.S. Jayakumar, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 72 (2009) 654–662. [37] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899–926. [38] J.P. Foster, F. Weinhold, J. Am. Chem. Soc. 102 (1980) 7211–7218. [39] F. Weinhold, C.R. Landis, Valency, Bonding: A Natural Bond Orbital Donor– Acceptor Perspective, Cambridge University Press, Cambridge, New York, Melbourr, 2005. pp. 215–274. [40] J.A. Pople, H.B. Schlegel, R. Krishnan, D.J. Defrees, J.S. Binkley, M.J. Frisch, R.A. Whiteside, R.F. Hout, W.J. Hehre, Int. J. Quantum Chem. 15 (1981) 269–278. [41] A.T. Dubis, S.J. Grabowski, D.B. Romanowska, T. Misiaszek, J. Leszczynski, J. Phys. Chem. A 106 (2002) 10613–10621. [42] P. Pulay, G. Fogarasi, F. Pang, J.E. Boggs, J. Am. Chem. Soc. 101 (1979) 2550– 2560. [43] M.R. Anoop, P.S. Binil, S. Suma, M.R. Sundarsanakumar, S. Mary, H.T. Varghese, C.Y. Panicker, J. Mol. Struct. 969 (2010) 48–54. [44] R.M. Silverstein, F.X. Webster, Spectrometric Identification of Organic Compounds, sixth ed., Jon Wiley Sons Inc., New York, 1963. pp. 71–109. [45] D. Gambino, L. Otero, M. Vieites, M. Boiani, M. Gonzalez, E.J. Baran, H. Cerecetto, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 68 (2007) 341– 348. [46] N. Sundaraganesan, S. Ayyappan, H. Umamaheswari, B.D. Joshua, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 66 (2007) 17–27. [47] J.A. Padrón, R. Carasco, R.F. Pellón, J. Pharm. Pharmaceut. Sci. 5 (2002) 258– 266. [48] R.P. Verma, C. Hansch, Bioorg. Med. Chem. 13 (2005) 2355–2372. [49] R.P. Verma, A. Kurup, C. Hansch, Bioorg. Med. Chem. 13 (2005) 237–255. [50] N. Uniyal, M. Sharma, B. Sharma, R.B. Tripathi, Int. J. Chem. Tech. Res. 2 (2010) 1468–1472. [51] R.N. Singh, P. Rawat, S. Sahu, J. Mol. Struct. 1065 (2014) 99–107. [52] P. Rawat, R.N. Singh, J. Mol. Struct. 1075 (2014) 462–470. [53] P. Rawat, R.N. Singh, J. Mol. Struct. 1074 (2014) 201–212. [54] R.N. Singh, P. Rawat, J. Mol. Struct. 1054–1055 (2013) 65–75. [55] R.N. Singh, A. Kumar, R.K. Tiwari, P. Rawat, R. Manohar, Struct. Chem. 24 (2013) 713–724. [56] R.N. Singh, P. Rawat, S. Sahu, Spectrochim. Acta Part A 135 (2015) 1162–1168. [57] R.N. Singh, P. Rawat, S. Sahu, J. Mol. Struct. 1076 (2014) 437–445. [58] R.N. Singh, A. Kumar, R.K. Tiwari, P. Rawat, Spectrochim. Acta Part A 112 (2013) 182–190.

P. Rawat, R.N. Singh / Journal of Molecular Structure 1084 (2015) 326–339 [59] R.N. Singh, A. Kumar, R.K. Tiwari, P. Rawat, V.P. Gupta, J. Mol. Struct. 1035 (2013) 427–440. [60] R.N. Singh, A. Kumar, P. Rawat, A. Srivastsva, J. Mol. Struct. 1049 (2013) 419– 428. [61] C.R. Zhang, H.S. Chen, G.H. Wang, Chem. Res. Chin. U 20 (2004) 640–646. [62] Y. Sun, X. Chen, L. Sun, X. Guo, W. Lu, Chem. Phys. Lett. 381 (2003) 397–403. [63] O. Christiansen, J. Gauss, J.F. Stanton, Chem. Phys. Lett. 305 (1999) 147–155.

[64] [65] [66] [67]

339

D.A. Kleinmann, Phys. Rev. 126 (1962) 1977–1979. R.N. Singh, P. Rawat, A. Kumar, J. Mol. Struct. 1061 (2014) 140–149. J.L. Oudar, D.S. Chemla, J. Chem. Phys. 66 (1997) 2664–2668. M.J. Frisch et al., Gaussian 09, Revision B.01, Gaussian Inc., Wallingford, CT, 2010. [68] Gauss-View 5.09 program, Gaussian Inc., Wallingford, CT, 06492 USA. [69] E.J.H. Chu, T.C. Chu, J. Org. Chem. 19 (1954) 266–269.