Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1194–1205

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Molecular conformational stability and Spectroscopic analysis of Parared with experimental techniques and quantum chemical calculations R. Srinivasaraghavan a, S. Thamaraikannan a, S. Seshadri b,⇑, T. Gnanasambandan c a

Department of Physics, SCSVMV University, Enathur, Kanchipuram 631 561, India Department of Physics, L.N. Govt. College, Ponneri 601 204, India c Department of Physics, Pallavan College of Engineering, Kanchipuram 631502, India b

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

 Molecular structure of Parared and its

Conformer C3 of parared.

conformers were investigated.  Spectroscopic properties of molecule were examined by FT-IR, and FT-Raman techniques.  The complete vibrational assignments are performed on the basis of the potential energy distribution (PED).  Nonlinear optical properties and natural bond orbital analysis were investigated.

a r t i c l e

i n f o

Article history: Received 28 April 2014 Received in revised form 2 July 2014 Accepted 18 July 2014 Available online 16 September 2014 Keywords: Parared PED NBO NLMO MEP

a b s t r a c t The complete vibrational assignment and analysis of the fundamental modes of Parared was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically from the optimized geometry of the compound from the DFT–B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO–LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated. Ó 2014 Elsevier B.V. All rights reserved.

Introduction Parared is otherwise called as Paranitraniline red, is a chemical dye. Chemically, the dye is similar to Sudan. It dyes cellulose fabrics as brilliant red. The reaction rate of the dye is not very fast. ⇑ Corresponding author. Tel.: +91 9445257477. E-mail address: [email protected] (S. Seshadri). http://dx.doi.org/10.1016/j.saa.2014.07.046 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

The dye can be washed away easily from cellulose fabrics if not dyed correctly [1]. Chemically Parared is also called as 1-[(E)(4-Nitrophenyl) diazenyl-2-naphthol. The additive is mainly used to color waxes, petrol, oils, and polishes. Sudan has also been adopted for coloring various foodstuffs, including particular brands of curry powder and chillipowder. The study of vibrational spectra of substituted pyridines, mainly Parared, attracts the attention of spectrophysicists due to their wide application in Dyes. Several

R. Srinivasaraghavan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1194–1205

researchers have studied various investigations on the title compounds so far [2,3]. Rubaie and Jameel [4] studied the Synthesis and characterization of Azo dye like Parared and its derivatives. Ajani et al. [5] have studied Synthesis and Spectroscopic Study of Naphtholic and Phenolic Azo Dyes. Studies related to vibrational Spectroscopic investigation and assignments using ab initio and DFT techniques for the title compound are not reported and analyzed in the literature. Hence in this study, we set out experimental and theoretical investigation of the vibrational and electronic transitions of Parared. In the ground state theoretical geometrical parameters, IR and Raman spectra, HOMO and LUMO energies of title molecule were calculated by using Gaussian 03W program. Detailed interpretations of the vibrational spectra of the Parared have been made on the basis of the calculated potential energy distribution (PED). The experimental results (IR and Raman spectra) were supported by the computed results, comparing with experimental characterization data; vibrational wavenumbers are in fairly good agreement with the experimental results. The redistribution of electron density (ED) in various bonding, antibonding orbitals and E(2) energies have been calculated by natural bond orbital (NBO)/natural localized molecular orbital (NLMO) analysis to give clear evidence of stabilization originating from the hyper conjugation of various intra-molecular interactions. By analyzing the density of states, the molecular orbital compositions and their contributions to the chemical bonding were studied. The study of HOMO, LUMO analysis has been used to elucidate information regarding charge transfer within the molecule. Moreover, the Mulliken population analyses of the title compound have been calculated and the results have been reported. The experimental and theoretical results supported each other, and the calculations are valuable for providing a reliable insight into the vibrational spectra and molecular properties. Experimental The compound Parared was purchased from Sigma–Aldrich Chemical Company, USA and used as such without further purification to record FTIR and FT Raman spectra. The FTIR spectrum of the compounds is recorded in the region 4000–400 cm1 in evacuation mode on Bruker IFS 66V spectrophotometer using KBr pellet technique (solid phase) with 4.0 cm1 resolutions. The FT-Raman spectra of these compounds are also recorded in the same instrument with FRA 106 Raman module equipped with Nd: YAG laser source operating at 1.064 lm line widths with 200 mW power. The spectra are recorded in the range of 3500–100 cm1 with scanning speed of 30 cm1 min1 of spectral width 2 cm1. The frequencies of all sharp bands are accurate to ±1 cm1. The spectral measurements were carried out at Sophisticated Analytical Instrumentation Facility, IIT, Chennai, India. Computational details A complete information regarding the structural characteristics and the fundamental vibrational modes of Parared, has been carried out using the B3LYP correlation functional calculations. The calculations of geometrical parameters in the ground state were performed using the Gaussian 03 [6] program. DFT calculations were carried out with Becke’s three-parameter hybrid model [7] using the Lee–Yang–Parr correlation [8] functional (B3LYP) method. The geometry optimization was carried out using the initial geometry generated from standard geometrical parameters at B3LYP method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The optimized geometry was determined by minimizing the energy with respect to all geometrical parameters without imposing

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molecular symmetry constraints. Harmonic vibrational wavenumbers were calculated using analytic second derivatives to confirm the convergence to minima in the potential surface. At the optimized structure of the examined species, no imaginary wavenumber modes were obtained, proving that a true minimum on the potential surface was found. The calculated frequencies are scaled according to the work of Rauhut and Pulay [9,10], a scaling factor of 0.9631 for B3LYP/6-31G(d,p) and 0.967 for B3LYP/6-311++G(d,p). According to Scaled Quantum Mechanics (SQM) procedure using selective scaling in the natural internal coordinate representation [11,12], the transformation of force field; subsequent normal coordinates analysis and calculation of the Potential Energy Distribution (PED) were done on a PC with the MOLVIB program (version V7.0-G77) written by Sundius [13–15]. By the use of GAUSSVIEW molecular visualization program [16] along with available related molecules; the vibrational frequency assignments were made by their PED with a high degree of confidence. The PED elements provide a measure of each internal coordinate’s contribution to the normal coordinates. Results and discussion Molecular geometry In order to find the most optimized geometry, the energies were carried out for Parared, using B3LYP/6-311++G(d,p) method and basis set for various possible conformers. There are three conformers for Parared. The computationally predicted various possible conformers obtained for the compound Parared is shown in Fig. 1. The total energies obtained for these conformers were listed in Table 1. It is clear in Table 1, the structure optimizations have shown that the conformer C3 have produced the global minimum energy of 344.9246 KJ/Cal. Therefore, C3 form is the most stable conformer than the other conformers. The optimized molecular structure with the numbering of atoms of the Parared is shown in Fig. 2. The most optimized structure parameters of Parared calculated by DFT-B3LYP levels with the 6-31G(d,p) and 6-311++G(d,p) basis set are listed in Table 2 in accordance with the atom numbering scheme given in Fig. 2. The optimized molecular structure of Parared belongs to C1 point group symmetry. Table 2 compares the calculated bond lengths and angles for Parared with those experimentally available from literature value [17]. From the theoretical values, we can find that most of the optimized bond angles are slightly differ from the experimental values, due to the theoretical calculations belong to isolated molecules in gaseous phase and the experimental results belong to molecules in solid state. The theoretical values for the Parared molecule were compared with the experimental values by means of the root mean square deviation values. Comparing the B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) methods, most of the bond lengths and bond angles are the same in both the methods. The inclusion of diffusion and polarization functions is important to have a better agreement with experimental geometry. Vibrational assignments The molecular structure of Parared belongs to C1 point group symmetry. For C1 symmetry there would not be any relevant distribution. The molecule Parared consists of 33 atoms and expected to have 93 normal modes of vibrations of the same A species under C1 symmetry. These modes are found to be IR and Raman active suggesting that the molecule possesses a non-Centro symmetric structure, which recommends the title compound for nonlinear optical applications. The harmonic vibrational modes calculated for Parared at B3LYP level using the 6-31G(d,p) and 6-311++G(d,p) basis set along with

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Potential energy distribution have been summarized in Tables 3. The observed FTIR and FT Raman bands for various modes of vibrations of Parared are assigned and are presented in Table 3 along with the DFT data. The force fields thus determined were used to calculate the vibrational potential energy distribution (PED) using the latest version of MOLVIB program [13–15]. The experimental FT-IR and FT-Raman spectra with corresponding theoretically simulated IR and Raman spectra of Parared as shown in Figs. 3 and 4 respectively, where the calculated infrared intensities and Raman intensities are plotted against the vibrational frequencies. In the spectra, the theoretically simulated spectra are more regular than the experimental ones because many vibrations presenting in condensed phase lead to strong perturbation of infrared and Raman intensities of many other modes. The RMS error of the observed and calculated frequencies (unscaled) of Parared is quite obvious since the frequencies are calculated on the basis of quantum mechanical force fields usually differ appreciably from observed frequencies. This is partly due to the neglect of anharmonicity and partly due to the approximate nature of the quantum mechanical methods. In order to reproduce the calculated frequencies, the scale factors were refined and optimized via a least squares refinement algorithm.

C1

OAH Vibrations The OAH group gives rise to three vibrations (stretching, in-plane bending and out-of-plane bending vibrations). The OAH group vibrations are likely to be the most sensitive to the environment, so they show pronounced shifts in the spectra of the hydrogen bonded species. The precise positions of OAH bond are dependent on the strength of hydrogen bond. The non-hydrogen bonded or free hydroxyl group absorbs strongly in the 3700–3584 cm1 region, while the existence of intermolecular hydrogen bond formation can lower the OAH stretching frequency to the 3550–3000 cm1 region, with the increase in IR intensity and broadness [18,19]. In this study the O–H stretching modes were calculated at 3394 in FTIR and 3395 in FT Raman spectrum of Parared and assigned to OAH stretching mode of vibration.

C2

C3

Fig. 1. Various possible conformers of Parared.

Table 1 Total energies of different conformations of Parared calculated at the B3LYP/ 6-311++G(d,p) level of theory. Sl. no

Conformers

Energy (KJ/mol)

1 2 3

C1 C2 C3

681.2857 515.0162 344.9346

CAH Vibrations The substituted benzene like molecule gives rise to CAH stretching, CAH in-plane and CAH out-of-plane bending vibration. In the aromatic compounds, the carbon–hydrogen stretching vibrations normally occur at 3250–3000 cm1 [20]. Heterocyclic compound CAH vibration absorption bands are usually weak; in many cases it is too weak for detection. The bands due to CAH in-plane bending vibrations interact somewhat with CAC stretching vibrations is observed as a number of bands in the region 1450–1100 cm1. The CAH out-of-plane bending vibrations occur in the region 900–667 cm1 [20,21]. In this region the vibrations are not found to be affected due to the nature and position of the substituent [22]. In the present work, the bands observed at 3223 cm1 and 3189 cm1 in the Parared compound have been assigned to CAH stretching vibration. Apart from the mentioned values other vibrations in the same range are assigned to CAH asymmetric and symmetric vibrations respectively. The CAH bending vibrations appear at two distinct regions 1480–1300 cm1 and 1100–900 cm1, due to in plane and out of plane bending vibrations respectively [23,24]. The band position observed at 1474 cm1 and 1082 cm1 in experimental spectrum of Parared are assigned to CAH in plane and out of plane bending vibrations The wavenumbers calculated through DFT techniques are in good agreement with the experimental data [23]. CAN vibrations The identification of CAN stretching vibration is a very difficult task, since the mixing of bands is possible in this region. The FT

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Fig. 2. Structure of Parared.

Raman band observed at 1323 cm1 in Parared has been designated to the CAN stretching mode of vibration. These assignments are made in accordance with the assignment proposed by Abkowicz-Bienko et al. [25]. The CAN stretching band assigned at 1319 cm1 in 2,6-dibromo-4-nitroaniline by Krishnakumar and Balachandran [26], Raja et al. [27] have identified the FTIR band at 1342 cm1 due to CAN in theophylline. Gunasekaran et al. [28] have observed the CAN stretching band at 1312 cm1 in benzocaine. The calculated value at 1325 cm1 of Parared is in excellent agreement with the observed value for the corresponding mode of vibration. CAC vibrations The CAC aromatic stretching vibration gives rise to characteristic bands in both the observed IR and Raman spectra, covering the spectral range from 1600 to 1400 cm1. The IR bands located at 1579, 1545, 1502 cm1 and 1352 cm1; the Raman bands centered at 1588, 1545, 1503 and 1352 cm1 have been assigned to CAC stretching vibrations. Of these bands, 1545 cm1 have appeared characteristically strong in the IR and Raman spectra. The calculated bands at B3LYP level in the same region are in excellent agreement with experimental observations of both in FTIR and FT Raman spectra of Parared [29–31]. The ring in plane vibrations has given rise to weak bands across the low wavenumber region, that is to say, below 1000 cm1. The bands at 866 cm1 and at 965 cm1 have been assigned to CAC in plane bending vibrations. As is seen from Table 4 the predicted vibrational bands agree well with the observed ones. Other molecular properties

b is calculated for the title compound by taking into account the Kleimman symmetry relations and the square norm of the cartesian expression for the b tensor [34]. The first order hyperpolarizability (b) of this novel molecular system and the related properties (a0 and Da) of Parared were calculated, based on the finite field approach. The complete equations for calculating the magnitude of the total static dipole moment l, the mean polarizability a0, the anisotropy of the polarizability Da, and the mean first order hyperpolarizability b, using the x, y, z components are defined as follow: 1=2

l ¼ ðl2x þ l2y þ l2z Þ b ¼ ðb2x þ b2y þ b2z Þ

a0 ¼

1=2

axx þ ayy þ azz 3 1

1

Da ¼ 22 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xx 2 where

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bz ¼ bzzz þ bxxz þ byyz The components of polarizability and the first order hyperpolarizability of the title compound can be seen in Table 4. The calculated value of first hyperpolarizability shows that Parared might have the NLO properties.

NLO properties NBO/NLMO analysis Many organic molecules that containing conjugated p electrons are characterized hyperpolarizabilities have been analyzed by means of vibrational spectroscopy [32,33]. Both the B3LYP/ 6-31G(d,p) and B3LYP/6-311++G(d,p) method has been used for the prediction of first order hyperpolarizability (b) of the title compound. The tensor components of the static first order hyperpolarizability (b) were analytically calculated by using the same method as mentioned above. From the computed tensorial components,

NBO (natural bond orbital) analysis provides an efficient method for studying intra and inter molecular bonding and interaction among bonds, and also provides a convenient basis for investigation charge transfer or conjugative interactions in the molecular system [32]. By the use of the second-order bond– antibond (donor–acceptor) NBO energetic analysis, insight in the most important delocalization schemes was obtained. The change

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Table 2 Molecular parameters of Parared. Molecular parameters Bond lengths C1AC2 C1AC10 C1AN12 C2AC3 C2AO11 C3AC4 C3AH23 C4AC5 C4AH24 C5AC6 C5AC10 C6AC7 C6AH25 C7AC8 C7AH26 C8AC9 C8AH27 C9AC10 C9AH28 O11AH29 N12AN13 N13AC14 C14AC15 C14AC19 C15AC16 C15AH30 C16AC17 C16AH31 C17AC18 C17AN20 C18AC19 C18AH32 C19AH33 N20AO21 N20AO22 Bond angles C10AC1AC2 N12AC1AC2 N12AC1AC10 C3AC2AC1 O11AC2AC1 O11AC2AC3 C4AC3AC2 H23AC3AC2 H23AC3AC4 C5AC4AC3 H24AC4AC3 H29AO11AC2 C4AC3AH23 C3AC4AC5 H24AC4AC3 H24AC4AC5 C6AC5AC4 C10AC5AC4 C10AC5AC6 C7AC6AC5 H25AC6AC5 C9AC10AC5 H25AC6AC7 C8AC7AC6 H26AC7AC6 H26AC7AC8 C9AC8AC7 H27AC8AC7 H27AC8AC9 C10AC9AC8 H28AC9AC8 H28AC9AC10 C14AN13AN12 C15AC14AN13 C19AC14AN13 C19AC14AC15

Table 2 (continued)

Expt.

B3LYP/ 6-31G(d,p)

B3LYP/ 6-311++G(d,p)

1.408 1.446 1.395 1.417 1.353 1.372 1.088 1.419 1.086 1.419 1.430 1.376 1.087 1.414 1.086 1.379 1.086 1.419 1.082 0.968 1.267 1.416 1.404 1.408 1.389 1.084 1.394 1.082 1.398 1.468 1.387 1.083 1.083 1.232 1.232

1.397 1.442 1.403 1.417 1.352 1.374 1.087 1.417 1.086 1.419 1.428 1.375 1.086 1.414 1.085 1.379 1.086 1.420 1.082 0.963 1.261 1.419 1.398 1.408 1.383 1.084 1.391 1.081 1.396 1.468 1.388 1.081 1.082 1.232 1.231

1.408 1.446 1.395 1.417 1.353 1.372 1.088 1.419 1.086 1.419 1.430 1.376 1.087 1.413 1.086 1.379 1.086 1.419 1.082 0.968 1.267 1.416 1.404 1.408 1.389 1.085 1.394 1.082 1.398 1.468 1.387 1.083 1.083 1.232 1.232

118.850 126.330 119.763 120.037 120.420 119.530 120.301 118.478 120.220 121.067 119.867 108.508 120.344 121.495 119.856 119.066 121.457 118.735 119.808 120.753 118.583 118.039 120.663 119.573 120.415 120.012 121.003 119.526 119.470 120.823 120.623 118.554 113.646 115.281 124.895 119.803

118.900 126.400 119.800 120.900 118.600 119.700 122.100 117.385 119.300 121.000 118.600 109.500 120.400 121.000 119.800 119.200 121.500 118.700 119.800 120.700 118.700 118.200 120.500 119.600 120.600 119.800 121.100 119.400 119.600 120.600 120.200 119.200 114.600 115.300 124.200 120.400

118.900 126.300 120.000 120.400 118.800 120.000 122.000 117.900 119.500 121.300 118.500 108.500 120.200 121.100 119.900 119.100 121.500 118.700 119.800 120.800 118.600 118.000 120.700 119.600 120.400 120.000 121.000 119.500 119.500 120.800 120.600 118.500 113.600 115.300 124.900 119.800

Molecular parameters

Expt.

B3LYP/ 6-31G(d,p)

B3LYP/ 6-311++G(d,p)

C16AC15AC14 H30AC15AC14 C18AC19AC14 H33AC19AC14 H30AC15AC16 C17AC16AC15 H31AC16AC15 H31AC16AC17 C18AC17AC16 N20AC17AC16 N20AC17AC18 C19AC18AC17 H32AC18AC17 O21AN20AC17 O22AN20AC17 H32AC18AC19 H33AC19AC18 O22AN20AO21

120.567 118.212 120.037 119.003 121.221 118.519 121.987 119.493 122.055 119.001 118.943 119.008 119.194 117.747 117.756 121.798 120.958 124.496

120.300 118.800 119.700 119.800 120.900 118.400 121.400 120.100 122.200 118.900 118.900 119.000 119.800 117.700 117.700 121.200 120.500 124.600

120.600 118.200 120.000 119.000 121.200 118.500 122.000 119.500 122.100 119.000 118.900 119.000 119.200 117.700 117.800 121.800 121.000 124.500

in electron density (ED) in the (r*, p*) antibonding orbitals and E(2) energies have been calculated by natural bond orbital (NBO) analysis [32] using DFT methods to give clear evidence of stabilization originating from various molecular interactions. NBO analysis has been performed on Parared (Parared) in order to elucidate intramolecular hydrogen bonding, intramolecular charge transfer (ICT) interactions and delocalization of p-electrons. The hyperconjugative interaction energy was deduced from the second-order perturbation approach [33].

Eð2Þ ¼ nr

F ij 2 ðrjFjrÞ2 ¼ nr er  r DE

where (r|F|r)2 or F 2ij is the Fock matrix element between the i and j NBOs, r and er are the energies of r and r* NBOs, and nr is the population of the donor r orbital. In Table S1 (Supplementary material), the perturbation energies of significant donor–acceptor interactions are presented. The larger the E(2) value, the intensive is the interaction between electron donors and electron acceptors. In Parared, the interactions between the first lone pair of nitrogen N1 and the antibonding of C8AC13 have the high E(2) value around 26.34 kcal/Mol. The other significant interactions giving stronger stabilization to the structure are the interactions between antibonding of C2AC3 between the first lone pair of nitrogen N1. Table 6 gives the occupancy of electrons and p-character [34] in significant NBO natural atomic hybrid orbitals. In CAH bonds, the hydrogen atoms have almost 0% of p character. On contrary, almost 100% p-character was observed in both the atoms of all the p bonding and antibonding between C2AC3, C4AC5, C6AC7, C8AC13, C9AC10 and C11AC12. Similarly, 100% p-character was observed in the first lone pair of N1 and in the third lone pair of Br14. The natural localized molecular orbital (NLMO) analysis has been carried out since they show how bonding in a molecule is composed from orbitals localized on different atoms. The derivation of NLMOs from NBOs gives direct insight into the nature of the localized molecular orbital’s ‘‘delocalization tails’’ [34,35]. Table S2 (Supplementary material) shows significant NLMO’s occupancy, percentage from parent NBO and atomic hybrid contributions of Parared calculated at B3LYP level using 6-31G(d,p) basis set. Among the bonded orbitals, the NLMO of BD(2) C2-C3 is the most delocalized and has only 81% contribution from the localized BD(2) C2-C3 parent NBO, and the delocalization tail (18%) consists of the hybrids of C4, C5, C6 and C7. Similarly, the BD (2)

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Table 3 Vibrational assignments of Parared using B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p). Experimental 1

IR m cm

410 446 453 465 469 491 550 571 579 588 615 636 669 686 733 749 775 787 833 842 858 866 908 934 953 964 976 988 1010 1048 1082 1101 1105 1115 1117 1126 1128 1160 1192 1205 1238 1263 1283 1290 1292 1325 1332 1352 1398 1405 1452 1474 1506 1530 1545 1553 1568 1579

Calculated using B3LYP/6-31G(d,p) 1

Raman m cm

107 147 165 182 217 280 302 315 347 358 409

495 570

612 630 671 731

830 860

984

1105

1165 1201 1241

1323

1397 1449 1503 1545 1554

1

Calculated using B3LYP/6-311++G(d,p) 1

Cal. Val. m cm

IR intensity

Raman intensity

Cal. Val. m cm

IR intensity

Raman intensity

19 33 47 57 88 110 149 166 181 215 280 304 313 344 359 409 446 453 465 469 491 549 570 579 589 614 636 669 689 733 746 776 787 833 843 859 866 908 933 952 965 976 982 1009 1045 1080 1099 1107 1114 1116 1127 1128 1163 1191 1203 1239 1264 1282 1290 1293 1325 1332 1352 1399 1407 1451 1473 1502 1529 1543 1555 1569 1579

0.136 0.571 0.517 0.064 2.562 1.576 2.404 7.517 1.455 8.738 5.024 28.650 92.155 10.452 3.391 1.585 9.173 10.964 0.984 2.639 4.451 9.878 6.043 2.247 1.921 5.406 4.799 10.771 0.317 1.560 13.138 11.409 5.219 5.257 11.600 41.341 7.456 54.375 9.575 0.060 53.494 2.111 23.537 22.212 49.676 0.007 1.639 5.076 2.370 3.704 0.106 0.236 13.511 0.845 64.386 41.263 19.960 0.954 11.334 23.078 25.220 13.756 5.470 99.811 3.978 0.640 77.471 37.994 12.124 1.127 21.605 99.425 67.451

11.704 1.612 6.929 1.261 4.738 1.348 2.118 12.513 0.964 0.466 8.498 6.315 2.501 2.458 2.011 1.275 3.342 2.771 0.510 6.982 6.436 3.359 11.017 3.248 6.515 0.388 1.817 2.777 10.377 4.002 22.847 2.654 2.224 5.073 6.867 14.639 3.895 3.623 3.399 3.221 25.913 3.783 8.342 25.697 36.608 1.350 0.306 10.516 14.439 28.292 2.757 1.162 96.284 7.327 14.411 49.788 35.223 46.795 20.937 18.749 47.391 49.472 28.243 12.492 94.005 52.766 33.323 46.486 38.082 71.286 39.848 6.928 31.378

19 34 46 60 90 107 149 165 182 214 281 303 312 345 360 407 445 453 464 470 491 550 570 578 589 615 637 669 689 734 745 777 789 832 843 859 866 909 932 950 965 975 983 1010 1046 1081 1099 1102 1113 1118 1126 1128 1167 1193 1203 1241 1263 1282 1291 1295 1327 1335 1349 1397 1408 1456 1475 1504 1529 1545 1556 1568 1581

0.158 0.119 0.364 0.051 0.504 2.802 3.296 4.846 3.568 2.628 4.974 26.112 89.716 8.859 3.897 1.911 7.188 12.649 1.501 4.029 6.947 10.896 6.297 2.558 1.170 3.471 4.881 13.243 0.537 1.769 13.551 8.870 7.261 5.880 15.794 42.272 8.562 52.345 8.818 1.446 51.685 1.617 21.328 17.331 40.452 0.848 2.160 4.261 1.528 3.649 0.101 1.573 19.870 1.668 76.003 35.181 12.212 0.583 12.363 28.662 24.674 10.793 3.178 92.835 7.183 1.838 65.818 32.960 11.489 3.149 24.725 93.637 67.839

6.697 4.365 5.431 0.950 4.681 1.717 7.101 10.698 0.641 1.284 5.172 7.630 2.108 1.879 1.093 2.510 4.587 3.826 0.409 6.131 7.929 6.194 15.690 7.478 6.041 0.233 7.816 17.444 11.779 3.593 14.535 1.317 5.162 8.044 15.591 11.087 3.640 1.959 2.969 5.820 26.743 2.899 21.382 28.574 41.900 0.847 0.282 13.652 21.973 30.189 1.868 2.348 98.047 7.300 17.578 48.576 33.058 58.846 16.883 14.678 59.973 45.815 24.086 19.919 85.572 58.801 32.676 31.061 37.487 65.787 38.541 5.003 32.544

Assignment with PED %

s ring (19) b ring (11) + sCN(57) Ring breathing(13) s CN (29) x N N (34) + cCH(8) a CO (28) + b CCN(30) Ring breathing (21) s N N (18) + b CCN(24) a C N (32) + cCH(17) Ring breathing (12) b C N (33) + cCH (9) b O H (48) sN C (7) b O H (74) + b NCC(13) d C O (35) + b CNC(9) s ring (23) + cCH(12) b Ring (22) + cCN (11) Ring breathing (25) b CCO(20) + b NCC(19) sR(69) + cCH(30) cCO(8) + sNC(5) cCN(15) + cCO(13) sNC(13) + b CCO(21) b R(12) + b CNO(10) mCN(8) + mCC(16) b CCO(30) + b R(19) cCO(59) + sNC(17) b CCH(13) + b R(63) b CCH(21) + mCC(6) b NCO(6) + b CCH(6) b R(27) + mCC(24) sR(50) + cCN(23) cCH(10) + b CNC(8) cCH(86) + cCN(8) mCC(32) + mCN(20) b R(15) + b CNN(8) cCH(86) + cCN(7) cCH(91) + sR(7) cCH(79) + mCC(25) b CNC(9) + b NCO(9) mCC(42) + mCN(21) cCH(91) + N@O scis(27) Rtrigd(19) + b CH(21) mCC(11) + mCN(6) b CCH(49) + b R(15) b R(33) + mCC(26) cCO(19) + b CCH(9) mCC(55) + b CCH(20) mCC(63) + b CCH(29) b CH(79) + mCC(28) b CH(68) + mCC(19) b CCH(64) + mCC(31) mCC(27) + mCN(12) b CCH(64) + mCC(27) b CCH(79) + mCC(16) mCN(39) + mCC(32) b CNO(6) + b CCH(5) b CCH(8) + b CCO(6) mCN(38) + mCC(22) mCN(33) + mCC(32) b CNO(16) + b CCH(9) b CCH(80) + mCN(14) mCC(72) + mCC(15) b CCH(41) + mCC(9) mCN(14) + b COH(11) mCN(6) + b CNH(6) mNO2sym (64) b CCH(9) mCC(72)+mCN(15) CHipb(84) + mCC(23) mCC(34) + b CH(11) b R(9) + b CCN(5) mNO2asym (64) mCC(35) + b CH(23) (continued on next page)

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Table 3 (continued) Experimental

Calculated using B3LYP/6-31G(d,p)

Calculated using B3LYP/6-311++G(d,p)

IR m cm1

Raman m cm1

Cal. Val. m cm1

IR intensity

Raman intensity

Cal. Val. m cm1

IR intensity

Raman intensity

1589 1602 1630 1647 1665 2962 2983 3032 3068 3132 3165 3188 3202 3223 3245 3287 3331 3361 3394

1588

1588 1602 1632 1647 1666 2962 2982 3033 3067 3130 3165 3189 3204 3224 3242 3289 3331 3360 3393

2.914 59.710 94.031 77.525 49.005 18.322 54.289 98.741 32.941 12.409 0.519 12.434 26.491 37.883 1.544 6.641 0.272 0.632 0.393

11.555 68.886 76.522 9.873 72.095 9.990 45.142 40.667 99.959 95.865 32.573 53.883 63.660 70.184 53.184 80.568 27.108 54.192 16.277

1589 1603 1635 1647 1667 2965 2983 3037 3068 3132 3168 3189 3205 3223 3241 3287 3333 3356 3397

0.731 30.728 96.532 95.564 46.319 19.689 57.993 96.705 32.191 13.932 2.117 18.608 20.327 30.958 1.561 5.882 0.856 0.119 0.312

10.737 68.434 69.105 21.155 72.788 8.745 47.050 82.256 92.202 95.680 42.113 75.033 49.602 94.852 49.130 69.706 46.428 77.896 19.889

2967 2980 3067 3132 3189 3222 3245 3332 3395

Assignment with PED %

mCC(63) + b CH(26) mCC(62) + bCCH(23) mCC(54) + bCH(7) mNN(94) mNO2asym (63) mCH(99) m CHsym(97) m CHsym(96) m CHsym (99) m CHasym(97) m CHasym (99) mCH(99) m CHasym (99) mCH(99) mCH(99) m CHasym (99) m CHasym (98) m CHasym (98) m OH (97)

% Transmittance

(b) B3LYP/6-311++G(d,p)

(b) B3LYP/6-31G(d,p)

(a)

Wavenumber (cm-1) Fig. 3. Comparative (a) experimental and (b) theoretical IR spectra of Parared.

C8-C13 has delocalization tail (17%) consists of hybrids of C9, C10, C11 and C12. The NLMO of first lone pairs of nitrogen atom N1 is the most delocalized NLMO and has only 88% contribution from the localized LP(1) N1 parent NBO, and the delocalization tail (9%) consists of the hybrids of C2, C3, C8 and C13. This delocalization can also be observed in the perturbation theory energy analysis given in Table S3 (Supplementary material). Molecular electrostatic potential Molecular electrostatic potential and electrostatic potential is useful quantities to illustrate the charge distributions of molecules and used to visualize variably charged regions of a molecule. Therefore, the charge distributions can give information about how the molecules interact with another molecule. The molecular electrostatic potential is widely used as a reactivity map displaying most probable regions for the electrophilic attack of charged pointlike reagents on organic molecules [36]. The molecular electrostatic potential V(r) that is created in the space around a molecule by its nuclei and electrons is well established as a guide to molecular reactive behavior. It is defined by:

VðrÞ ¼

X A

ZA  ðRA  rÞ

Z

qðr0 Þ ðr 0  rÞ

dr

0

in which ZA is the charge of nucleus A, located at RA, q(r0 ) is the electronic density function for the molecule and r0 is the dummy integration variable [37]. At any given point r(x, y, z) in the vicinity of a molecule, the molecular electrostatic potential (MEP), V(r) is defined in terms of the interaction energy between the electrical charge generated from the molecule electrons and nuclei and a positive test charge (a proton) located at r [38]. In the graphic of total electron density surface mapped with the electrostatic potential, the sign of the electrostatic potential in a surface region is determined by the predominance of negative charges contribution or positive charges contribution. Accordingly, it is possible to identify regions more susceptible to an approximation of electrophilic molecules or nucleophilic molecules, so the molecular electrostatic potential map is commonly used as reactivity map. To predict regions more susceptible to approximation of either electrophiles or nucleophiles, MESP was calculated at the B3LYP/6-31G(d,p) is shown in Fig. 5. The importance of total electron density surface mapped with the electrostatic potential lies in

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Raman intensity

(b) B3LYP/6-311++G(d,p)

(b) B3LYP/6-31G(d,p)

(a)

Wavenumber (cm-1) Fig. 4. Comparative (a) experimental and (b) theoretical Raman spectra of Parared.

Table 4 The calculated l, a and b components of Parared. Parameters

B3LYP/6-31G(d,p)

B3LYP/6-311++G(d,p)

Parameters

B3LYP/6-31G(d,p)

B3LYP/6-311++G(d,p)

lx ly lz l axx axy ayy axz ayz azz atot Da

7.7650 2.5181 0.0528 8.1633 438.157 2.539 237.636 6.942 7.557 73.712 142.949 397.386

7.4156 2.9167 0.2380 7.7377 311.741 4.117 204.792 6.750 13.043 88.437 156.935 430.293

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz btot (esu)

736.656 545.425 85.053 19.476 33.196 3.877 7.352 8.105 4.353 0.611 1.21  1030

565.678 58.574 43.012 8.431 53.674 5.565 21.675 6.648 0.546 0.535 1.26  1030

Table 5 Mullikan atomic charges table of Parared. Atom

B3LYP/ 6-31G(d,p)

B3LYP/ 6-311++G(d,p)

Atom

B3LYP/ 6-31G(d,p)

B3LYP/ 6-311++G(d,p)

C C C C C C C C C C O N N C C C C

0.20474 0.42602 0.35634 0.09977 0.05731 0.12010 0.16456 0.14934 0.11885 0.03216 0.63373 0.33492 0.28539 0.22022 0.14930 0.10674 0.12666

0.22256 0.34834 0.14178 0.11992 0.09090 0.13178 0.08937 0.09057 0.11121 0.06032 0.51535 0.33594 0.30063 0.26291 0.09851 0.09806 0.25173

C C N O O H H H H H H H H H H H

0.11170 0.12987 0.52504 0.47232 0.47210 0.15397 0.16835 0.15524 0.15499 0.15626 0.17943 0.35269 0.19089 0.22052 0.21998 0.19773

0.10843 0.07532 0.38343 0.40309 0.39712 0.08619 0.09917 0.08780 0.09117 0.09336 0.11227 0.31918 0.11800 0.14082 0.13430 0.11462

positive, zero or negative regions. In GaussView visualizing program [10] the following spectral color scheme is used. So potential increases in the order: red < orange < yellow < green < cyan < blue. Therefore red indicates negative regions, blue indicates positive regions, while green appears over zero electrostatic potential regions. It is accepted that the negative (red) and the positive (blue) potential regions in the mapped MESP represent regions susceptible to approach electrophilic molecules or nucleophilic molecules, respectively. It can be seen that the most possible sites for electrophilic attack is H15. Negative regions of the studied molecule are found around the C5, C6 and C7 atoms indicating a possible site for nucleophilic attack. According to these calculated results, the MEP map shows that the negative potential sites are on electronegative atoms as well as the positive potential sites are around the hydrogen atoms. The contour map provides a simple way to predict how different geometries could interact and is shown in Fig. 6. Mulliken charge distribution

the fact that it simultaneously displays molecular size, shape, as well as positive or negative electrostatic potential regions in terms of color grading and is very useful in research of molecular structure with its physiochemical property relationship [39]. The different values of the electrostatic potential are represented by different colors. The range values for the color scale of the mapped MESP should be symmetrical to allow easy identification of negative (red) and the positive (blue) potential regions. The use of a symmetrical potential scale values eases the recognition of

The Mulliken populations show one of the simplest pictures of charge distribution. The Mulliken charges provide net atomic populations in the molecule while electrostatic potentials yield the electric field out of the molecule produced by the internal charge distribution. Thus, in the reactivity studies, Mulliken populations and MESP are complementary tools, and correlation between the schemes is expected [40]. However, Mulliken population analysis requires very careful because problems as large changes of the calculated atomic charges with small changes in the bases used and

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Table 6 Molecular properties of Parared. Molecular properties

EHOMO (eV) ELUMO (eV) EHOMO–LUMO gap (eV) Ionization potential (I) eV Electron affinity (A) eV

B3LYP

Molecular properties

6-31G(d,p)

6-311++G(d,p)

7.8755 0.9869 8.8625 7.8755 0.9869

5.8717 2.8281 3.0436 5.8717 2.8281

Chemical hardness (g) Softness(S) Chemical potential (l) Electronegativity (v) Electrophilicity index (x)

B3LYP 6-31G(d,p)

6-311++G(d,p)

4.4312 0.2257 3.4443 3.4443 5.9316

4.3499 0.2299 1.5218 1.5218 1.1579

For Mulliken charge distribution, the GaussView adopts the follow colors scheme: bright red for more negative charge and bright green for a more positive charge. The red hues illustrate negative charges while green hues expose positive charges. The charge distribution of the compound shows that carbon atom (C8) attached with nitrogen atoms have negative charges. All the hydrogen atoms have positive Mulliken charges. The atom C2 has the highest Mulliken charge (0.39624) when compared to other atoms. The nitrogen (N1) atoms are much more negative charge than the other atoms. The smallest Mulliken charge value (1.08219) was obtained for N1 atom. The Mulliken charge distribution and the MESP informations are concordant. Global and local reactivity descriptors

Fig. 5. Molecular electrostatic potential of Parared.

The Highest Occupied Molecular Orbitals (HOMOs) and Lowest– Lying Unoccupied Molecular Orbitals (LUMOs) are named as Frontier molecular orbitals (FMOs). The energy gap between the HOMOs and LUMOs is the critical parameters in determining molecular electrical transport properties helps in the measure of electron conductivity. To understand the bonding feature of the title molecule, the plot of the Frontier orbitals, the highest occupied molecular orbital HOMO and lowest unoccupied molecular orbital LUMO as shown in Fig. 7. The HOMO shows that the charge density localized mainly on carbonyl and amine group where as LUMO is localized on ring system. Gauss-Sum 2.2 Program [41] has been used to calculate group contributions to the molecular orbitals and prepare the density of the state (DOS) as shown in Fig. 8. The DOS spectra were created by convoluting the molecular orbital information with GAUSSIAN curves of the unit height. By using HOMO and LUMO energy values for a molecule, the global chemical reactivity descriptors of molecules such as hardness, chemical potential, softness, electronegativity and electrophilicity index as well as local reactivity have been defined [42–46]. Pauling introduced the concept of electronegativity as the power of an atom in a molecule to attract electrons to it. Hardness (g), chemical potential (l) and electronegativity (v) and softness are defined follows.

    1 @2E 1 @l VðrÞ ¼ VðrÞ 2 @N 2 2 @N   @E l¼ VðrÞ @N   @E VðrÞ v ¼ l ¼  @N

g¼

Fig. 6. The contour map of electrostatic potential of the total density of Parared.

the overestimation of the covalent character of a bond are common. So, in general, the absolute magnitude of the atomic charges has little physical meaning, on the other hand, their relative values can offer valuable information. The Mulliken charge distribution of the molecule was calculated at B3LYP level with 6-31G(d,p) and 6311++G(d,p) basis sets. Mulliken charge distribution graphically and structurally is shown in Figs. S1 and S2 (Supplementary material). The total atomic charges of Parared using B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) methods were listed in Table 5.

where E and V(r) are electronic energy and external potential of an N-electron system respectively. Softness is a property of a molecule that measures the extent of chemical reactivity. It is the reciprocal of hardness.

S¼

1

g

Using Koopman’s theorem for closed-shell molecules, g, l and v can be defined as

R. Srinivasaraghavan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1194–1205

HOMO DIAGRAM

1203

LUMO DIAGRAM

Fig. 7. Frontier molecular orbital of Parared.

Fig. 8. DOS spectrum of Parared.

g¼

IA 2

l¼

ðI þ AÞ 2

v¼

IþA 2

where A and I are the ionization potential and electron affinity of the molecules respectively. The ionization energy and electron affinity can be expressed through HOMO and LUMO orbital energies as I = EHOMO and A = ELUMO. Electron affinity refers to the capability of a ligand to accept precisely one electron from a donor. The ionization potential calculated by B3LYP/6-31G(d,p) and B3LYP/ 6-311++G(d,p) methods for Parared is 5.3863 eV and 5.4477 eV respectively. Considering the chemical hardness, large HOMO– LUMO gap means a hard molecule and small HOMO–LUMO gap means a soft molecule. One can also relate the stability of the molecule to hardness, which means that the molecule with least HOMO–LUMO gap means it, is more reactive. Recently Parr et al. [42] has defined a new descriptor to quantify the global electrophilic power of the molecule as an electrophilicity index (x), which defines a quantitative classification of the global electrophilic nature of a molecule Parr et al. [42] have proposed electrophilicity index (x) as a measure of energy lowering due to maximal electron flow between donor and acceptor. They defined electrophilicity index (x) as follows:

x¼

l2 2

Using the above equations, the chemical potential, hardness and electrophilicity index have been calculated for Parared and their values are shown in Table 6. The usefulness of this new reactivity quantity has been recently demonstrated in understanding the toxicity of various pollutants in terms of their reactivity and site selectivity [47–49]. The calculated value of electrophilicity index describes the biological activity of Parared. Temperature dependence of thermodynamic properties The statistical thermodynamics, like the standard thermodynamic functions such as heat capacity, entropy and enthalpy were calculated using perl script THERMO.PL [50] and are listed in Table 7. As observed from Table 7, the values of CP, H and S all increase with the increase of temperature from 100 to 1000 K, which is attributed to the enhancement of the molecular vibration as the temperature increases. The correlation equations between heat capacity (C°pm), entropy (S°m), enthalpy (H°m) changes and temperatures were fitted by quadratic formulas and the corresponding fitting

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Table 7 Thermo dynamical properties of Parared. T (K)

S (J/mol K)

100 200 298.15 300 400 500 600 700 800 900 1000

369.31 470.01 560.58 562.26 651.7 737.94 819.95 897.21 969.71 1037.66 1101.42

371.92 477.61 574.65 576.46 672.48 764.4 851.03 931.99 1007.44 1077.78 1143.5

References

CP (J/mol K)

ddH (kJ/mol)

112.23 188.84 270.62 272.16 352.13 421.28 478.04 524 561.39 592.17 617.81

7.51 22.48 45.01 45.51 76.8 115.57 160.64 210.82 265.15 322.88 383.41

116.05 201 290.94 292.6 376.94 447.01 502.8 547.05 582.57 611.55 635.54

7.67 23.4 47.55 48.09 81.67 122.99 170.59 223.17 279.71 339.46 401.86

factors (R2) for these thermodynamic properties are 0.9999, 0.9998 and 0.9998, respectively. The corresponding fitting equations are as follows and the correlation graphs of those shown in Fig. S3 (Supplementary material). 

S m ¼ 240:03433 þ 0:7328 T  1:79433  104 T 2 ðR2 ¼ 0:9999Þ 

C pm ¼ 15:26587 þ 0:65639 T  2:82786  104 T 2 ðR2 ¼ 0:9998Þ 

Hm ¼ 7:65942 þ 0:08696 T þ 1:73344  104 T 2 ðR2 ¼ 0:9998Þ All the thermodynamic data provide helpful information to further study of the title compounds. They compute the other thermodynamic energies according to the relationship of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermo chemical field. Notice: All thermodynamic calculations were done in gas phase and they could not be used in solution.

Conclusion A complete structural, thermodynamic, first-order hyperpolarizability, Mulliken population analysis, vibrational and electronic investigations of Parared have been carried out with FTIR and FTRaman Spectroscopic technique along with DFT/B3LYP method with different basis sets. The gas phase structure and conformational properties of Parared and its conformers were determined by quantum chemical calculations. It is found that molecule has three conformations. The equilibrium geometries and harmonic frequencies of Parared was determined and analyzed at the DFT level utilizing 6-31G(d,p) and 6-311++G(d,p) basis set, giving allowance for the lone pairs through diffuse functions. The difference between observed and calculated wavenumber values of the most of the fundamental modes is very small. Any discrepancy noted between the observed and the calculated vibrational band assignments may be due to the fact that the calculations have been actually done on a single molecule in the gaseous state contrary to the experimental values recorded in the presence of intermolecular interactions. The various intramolecular interactions that is responsible for the stabilization of the molecule was revealed by natural bond orbital analysis. The lowering of HOMO and LUMO energy gap clearly explicates the charge transfer interactions taking place within the molecule.

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.saa.2014.07.046.

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