Quantum mechanical study of the structure and spectroscopic (FTIR, FT-Raman), first-order hyperpolarizability and NBO analysis of 1,2-benzoxazol-3-ylmenthane sulfonamide

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 603–613

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Quantum mechanical study of the structure and spectroscopic (FTIR, FT-Raman), first-order hyperpolarizability and NBO analysis of 1,2-benzoxazol-3-ylmenthane sulfonamide S. Muthu a,⇑, G. Ramachandran b, E. Isac Paulraj c, T. Swaminathan d a

Department of Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602 105, Tamil Nadu, India Research Scholar Research and Development Centre, Bharathiyar University, Coimbatore, Tamil Nadu, India Department of Applied Physics, Pallavan College of Engineering, Kancheepuram 631 502, Tamil Nadu, India d Department of Chemical Engineering, Sri Venkateswara College of Engineering, Sriperumbudur 602 105, Tamil Nadu, India b c

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 vibrational assignment and

1,2-Benzoxazol-3-ylmenthane sulfonamide is used for adjunctive treatment of partial seizures in adults and neuropathic pain. It is chemically called as 1,2-benzoxazol-3-ylmenthane sulfonamide. An extensive work has been carried out on the title compound and its derivatives in recent year. At present, vibrational spectroscopy is used not only for functional group identification of organic compounds, but also to investigate the molecular conformation, reaction kinetics.

spectroscopic analysis have been carried out.  NBO analysis has been carried out to explain the interaction between donors and acceptors.  NLO behaviors were computed.  The HOMO and LUMO energy gap were theoretically predicated.  The molecular orbital contributions were studied.

a r t i c l e

i n f o

Article history: Received 21 December 2013 Received in revised form 22 February 2014 Accepted 25 February 2014 Available online 12 March 2014 Keywords: FTIR FT-Raman DFT NBO PED

a b s t r a c t Fourier transform infrared (FTIR) and FT-Raman spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide in the solid phase were recorded and analyzed. The molecular geometry, vibrational frequencies, infrared intensities, Raman activities and atomic charges were calculated using HF and density functional theory calculation (B3LYP) with standard 6-31G(d, p) basis set. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman spectra. The thermodynamic functions of the title compound were also performed. Stability of the molecule arising from hyper-conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The dipole moment (l), polarizability (a) and the hyperpolarizability (b) values of the molecule has been computed. Potential Energy Distribution (PED) were computed for the assignment of unambiguous vibrational fundamental modes. UV–vis spectrum of the compound was also recorded. The theoretical electronic absorption spectra have been calculated by TD-DFT/B3LYP using 6-31G(d,p) basis set. The HOMO and LUMO energy gap reveals that the chemical activity of the molecule. The molecular orbital contributions were studied by density of energy states (DOSs). Thermodynamic properties

⇑ Corresponding author. Tel.: +91 9443690138; fax: +91 4427162462. E-mail address: [email protected] (S. Muthu). http://dx.doi.org/10.1016/j.saa.2014.02.183 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

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(heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated. Finally, simulated FTIR and FT-Raman spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide showed good agreement with the observed spectra. Ó 2014 Elsevier B.V. All rights reserved.

Introduction 1,2-benzoxazol-3-ylmenthane sulfonamide is a sulfonamide anticonvulsant approved for use as an adjunctive therapy in adults with partial-onset seizures for adults; infantile spasm, mixed seizure types of Lennox Gastaut syndrome, myclonic and generalized tonic clonic seizure [1]. An open trail on 1,2-benzoxazol-3-ylmenthane sulfonamide in seven Parkinson’s disease patients had positive results [2]. Since then, it has been reported to treat the resting tremor that other therapies may leave behind [3]. It has also been studied for obesity with significant positive effects on body weight and used as a migraine preventative medication and has also been shown to be effective in some cases of neuropathic pain [4]. Molecular formula for 1,2-benzoxazol-3-ylmenthane sulfonamide is C8H8N2O3S. It belongs to C1 point group symmetry and soluble in water. An extensive work has been carried out on the title compound and its derivates in recent years [5,6]. The characteristic vibrational frequencies of this drug has been identified and assigned on the basis of their relative intensity, characteristic position and correlation of vibrational bands of related compounds. Its properties like storage condition, interactions with other trace elements were studied in details [7]. Literature survey reveals that to the best of our knowledge no ab initio HF/DFT wave number calculations of 1,2-benzoxazol-3-ylmenthane sulfonamide have been reported so far. Hence, we have undertaken detailed theoretical and experimental investigation of vibrational spectra of this molecule completely and to identify the various normal modes with greater wave number accuracy. Ab initio HF and density functional theory (DFT) calculations have been performed to support our wave number assignments. In addition, NBO analysis first order hyperpolarizability UV–vis studies along with HOMO and LUMO analysis and thermodynamic properties are also calculated at the HF(6-31G(d,p)) and B3LYP(6-31G(d,p)) level.

UV-1650PC, UV–vis regarding spectrometer. The UV pattern is taken from 105 molar solution of molecule, solved in ethanol as shown in Fig. 3. Computational details The entire calculations were performed at Hartree–Fock (HF) and density functional (DFT) levels on a Pentium IV personal computer using Gaussian 03W [8] program package invoking gradient geometry optimization [9]. The harmonic vibrational frequencies were calculated at the same level of theory for the optimized structures and obtained frequencies were scaled by HF/6-31G(d,p) 0.903 and B3LYP/6-31G(d,p) 0.961 [10]. Initial geometry generated from standard geometrical parameters was minimized without any constraint in the potential energy surface at Hartree–Fock level, adopting the standard 6-31G(d,p) basis set. This geometry was then re-optimized again at DFT levels, using the same basis set. The optimized structural parameters were used in the vibrational frequency calculation at DFT levels to characterize all stationary points as minima. We have used ab initio HF and DFT/B3LYP approach for the computation of molecular structure, vibrational frequencies and energies of optimized structures in the present work using GAUSSVIEW program with symmetry considerations along with available related molecules, vibrational frequency assignments were made with a high degree of accuracy. Next the spectra were analyzed in terms of the Potential Energy Distribution (PED) contributions by using the Vibrational Energy Distribution Analysis

Methodology Experimental details The compound under investigation namely 1,2-benzoxazol3-ylmenthane sulfonamide is purchased from Sigma–Aldrich chemicals, USA which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FTIR spectrum of the compound are recorded in Bruker IFS 66 V spectrometer in the range of 4000–400 cm1. The spectral resolution is ±2 cm1. The FT-Raman spectrum of 1,2-benzoxazol-3-ylmenthane sulfonamide is 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 spectrum is recorded in the range of 4000–100 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 experimental FTIR and FT Raman spectra along with the theoretically predicted FTIR using DFT/6-31G(d,p) and FT Raman spectra using HF/6-31G(d,p) level of calculations are shown in Figs. 1 and 2. The spectral measurements were carried out at Regional Sophisticated Instrumental Centre IIT, Chennai, India. The UV–vis spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide molecule are examined in the range of 200–400 nm in the SHIMADZU

Fig. 1. FTIR spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide (a) Experimental, (b) calculated B3LYP/ 6-31G(d,p) and (c) calculated HF/6-31G(d,p).

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Ii ¼

f ðt0  ti Þ4 Si ti ½1  expðhcti =kb TÞ

where t0 is the exciting frequency in cm1 ti is the vibrating wave number of the ith normal mode h, c and kb are the fundamental constants and f is a normalization factor for all peak intensities. The first hyperpolarizabilities (b0) of this novel molecular system, and related properties (b, a0 and a) of 1,2-benzoxazol3-ylmenthane sulfonamide were calculated using HF/6-31G(d,p) basis set, based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. Polarizabilities and hyperpolarizabilities characterize the response of a system in an applied electric field [16]. They determine not only the strength of molecular interactions (long-range inter induction, dispersion force, etc.) as well as the cross sections of different scattering and collision process but also the nonlinear optical properties (NLO) of the system [17,18]. First hyperpolarizability is a third rank tensor that can be described by 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [19]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3  3  3 matrixes is a tetrahedral. The components of b are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes

Fig. 2. FT-Raman spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide (a) experimental, (b) calculated B3LYP/ 6-31G(d,p) and (c) calculated HF/6-31G(d,p).

1 1 E ¼ E0  la F a aab F a F b  babc F a F b F c þ    2 6 where E0 is the energy of the unperturbed molecules, Fa the field at the origin la and aab babc are the components of dipole moments, polarizability and the first hyperpolarizabilities respectively. The total static dipole moments l, the mean polarizabilities a0, the anisotropy of the polarizabilities a and the mean first hyperpolarizabilities b, using the x, y and z components they are defined as: [17,18]. The total static dipole moment is 1=2

l ¼ ðl2x þ l2y þ l2z Þ

The isotropic polarizability is

a0 ¼

ðaxx þ ayy þ azz Þ 3

The polarizability anisotropy invariant is

a ¼ 21=2 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xx  Fig. 3. UV–vis spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide.

and the average hyperpolarizability is

b0 ¼ ðb2x þ b2y þ b2z Þ Program [11]. The mean linear hyper polarizability and mean first hyperpolarizability properties of the title compound were obtained molecular polarizabilities based on theoretical calculations. The natural bond orbital (NBO) calculations [12] were performed using NBO 3.1 program as implemented in the Gaussian 03W package at the above said level. In order to understand various second order interactions between the filled orbital of one subsystem and vacant orbital of another subsystem. This is a measure of the inter-molecular and intra-molecular delocalization or hyper conjugation. Prediction of Raman intensities and hyperpolarizability The Raman activities (Si) calculated with the Gaussian 03W program were subsequently converted to relative Raman intensities (Ii) using the following relationship derived from the theory of Raman scattering [13–15].

1=2

1=2

and

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bz ¼ bzzz þ bxxz þ byyz The total static dipole moment, polarizabilities and first order hyper-polarizabilities of 1,2-benzoxazol-3-ylmenthane sulfonamide were calculated. Supplementary Table S1 lists the values of the electric dipole moment (Debye) and dipole moment components, polarizabilities and hyperpolarizebilities of the1,2-benzoxazol-3-ylmenthane sulfonamide. In addition to the isotropic polarizabilities and polarizabilities anisotropy invariant were also calculated. The calculated value of dipole moment was found to be 3.109 at HF/6-31G(d,p) level. The polarizabilities and first order

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hyperpolarizabilities of 1,2-benzoxazol-3-ylmenthane sulfonamide are 288.95 a.u. 290.850 a.u. and 0.5205  1030 esu, 0.4691  1030 esu by B3LYP/6-31G(d,p) and HF/6-31G(d,p) levels, which are comparable with the reported values of similar derivatives [20]. The magnitude of the molecular hyperpolarizability b, is one of key factors in a NLO (non-linear optical) system. Total dipole moment of title molecule is approximately to those of urea and first order hyperpolarizebility of title molecule is greater than those of urea [21]. Hence we conclude that the title compound is an attractive object for future studies of nonlinear optical properties.

Table 1 Geometrical parameters optimized in 1,2-benzoxazol-3-ylmenthane sulfonamide 0 bond length (Å A) and bond angle (°) with 6-31G(d,p) basis set.

Results and discussion Molecular geometry The Molecular structure of 1,2-benzoxazol-3-ylmenthane sulfonamide is calculated by B3LYP and HF level with 6-31G(d,p) basis set shown in Table 1 in accordance with the atom numbering scheme given in Fig. 4. A general priority for reproducing the experimental bond lengths and bond angles [22] is not present among HF and DFT levels. All calculated geometrical parameters obtained at the DFT level of theory are in good agreement with the experimental structural parameters. The density functional calculation gives shortening of angles C1AC4AN3, C7AC8AH18, C9AC8AH18, C10AC9AH19, an increase of angles C5AC7AH17, C6AC10AH20, C8AC7AH17, C7AC8AC9, C8AC9 AC10, from 120° exactly at the substitution and other part0 of ring 0 respectively [23]. The C1AS11 (1.82 Å A) and S11AO12 (1.48 Å A) bond length 0are longer than the normal CAC bond length is about (1.49AÅ A) since these bonds play a bridge role between two phenyl groups. Further the results of our calculation showed that S11AO12 and S11AO13 bonds show typical double bond characteristics and all other bond lengths fall within the expected range. Some values deviates when comparing with the XRD data and these differences are probably due to intramolecular interactions in the solid state. As seen from Table 2 the optimized parameters are slightly over estimated from the experimental values due to the fact that the experimental results belong to the solid phase and theoretical calculations belong to isolated molecule in gas phase. Vibrational assignments The vibrational spectrum is mainly determined by the modes of the free molecule observed at higher wave numbers, together with the lattice (translational and vibrational) modes in the low wave number region. In our present study, we have performed a frequency calculation analysis to obtain the spectroscopic signature of 1,2-benzoxazol-3-ylmenthane sulfonamide. The 1,2benzoxazol-3-ylmenthane sulfonamide molecule consists of 22 atoms therefore they have 60 vibrational normal modes. All the frequencies are assigned in terms of fundamental, overtone and combination bands. Assignments have been made on the basis of Potential Energy Distribution (PED). The measured (FTIR and FT-Raman) wave numbers and assigned wave numbers of the some selected intense vibrational modes calculated at the HF and B3LYP level with basis sets 6-31G(d,p) along with their PED are given in Table 3. This reveals good correspondence between theory and experiment in main spectral features. The experimental and theoretical FTIR and FT-Raman spectra are shown in Figs. 1 and 2. The wave numbers calculated at the HF level are higher than the ones from B3LYP. Inclusion of IR and Raman spectra contain a number of bands at specific wave numbers. On the whole, the predicted vibrational wave numbers are in good agreement with the experimental results.

a

Molecular parameter

Experimentala

HF/6-31G(d,p)

B3LYP/6-31G(d,p)

C1AC4 C1AS11 C1AH15 C1AH16 O2AN3 O2AC6 N3AC4 C4AC5 C5AC6 C5AC7 C6AC10 C7AC8 C7AH17 C8AC9 C8AH18 C9AC10 C9AH19 C10AH20 S11AO12 S11AO13 N14AH21 N14AH22

1.49 1.80 1.09 1.09 1.40 1.35 1.31 1.44 1.40 1.40 1.39 1.38 1.08 1.41 1.08 1.39 1.08 1.08 1.46 1.46 1.01 1.06

1.39 1.78 1.07 1.06 1.41 1.36 1.21 1.42 1.46 1.40 1.39 1.46 1.07 1.40 1.08 1.42 1.09 1.07 1.52 1.47 1.02 1.05

1.38 1.82 1.05 1.07 1.42 1.37 1.11 1.41 1.39 1.39 1.42 1.49 1.08 1.41 1.09 1.41 1.01 1.08 1.48 1.39 1.09 1.08

Bond angle C4AC1AS11 C4AC1AH15 C4AC1AH16 C1AC4AN3 C1AC4AC5 S11AC1AH15 S11AC1AH16 C1AS11AO12 C1AS11AO13 H15AC1AH16 N3AO2AC6 O2AN3AC4 O2AC6AC10 C6AC5AC7 C5AC6AC10 C5AC7-C8 C5AC7AH17 C6AC10AH20 C8AC7AH17 C7AC8AC9 C7AC8AH18 C9AC8AH18 C8AC9AC10 C10AC9AH19 C9AC10AH20 O12AS11AO13 H21AN14AH22

115.30 111.90 110.30 119.40 130.50 103.50 106.20 106.40 107.90 109.20 108.30 107.70 126.70 120.00 123.40 117.50 120.80 121.60 121.63 121.40 119.50 119.10 121.90 119.10 122.50 121.80 112.30

116.60 111.70 116.30 119.50 132.40 103.80 107.40 106.80 108.40 109.40 108.60 109.70 125.50 120.00 123.60 119.00 120.36 121.30 121.40 121.48 120.50 119.80 122.10 119.58 121.80 121.50 114.80

115.08 112.10 114.60 119.80 129.50 106.60 108.40 108.20 110.50 111.70 110.50 111.40 126.90 121.64 125.80 119.58 120.50 121.00 121.62 121.50 120.50 119.90 120.00 119.99 121.74 121.97 112.50

Taken from Ref. [22].

CAH vibrations The hetero aromatic structure shows the presence of CAH stretching vibrations in the region 3100–3000 cm1. Which is the characteristic region for the ready identification of CAH stretching vibrations [24]. These vibrations are found to be affected due to the nature and position of the substituent’s. According to in the present study, the IR bands are observed in the range 3100– 2992 cm1 and one weak band observed at 2989 cm1 in Raman. Theoretically computed CAH vibrations by B3LYP/6-31G(d,p) method of scaled values is approximately coincides with experimental value. As indicated by the PED, these modes (Mode Nos. 3–8) involve more than 90% of contribution suggesting that they are pure stretching modes. The CAH in plane bending vibrations appear in the range 1300–1000 cm1 and out of plane bending vibrations occur in the range 1000–750 cm1 for substituted benzenes [25,26]. In

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the wide region 1035–245 cm1 both in aliphatic and aromatic [32] sulfides have a weak to medium band due to CAS stretching vibration in the region 710–570 cm1. In the present work the band observed at 702 cm1 in FTIR and 705 cm1 in FT-Raman are assigned to CAS stretching vibration. Theoretically computed values are found to be in good agreement with experimental results and listed in Table 2.

Fig. 4. Numbering system adopted in this study 1,2-benzoxazol-3-ylmenthane sulfonamide.

our title molecule weak to medium bands observed in FT-IR as well as in FT-Raman spectrum at 1316, 1309, 1188, 1157, 1062 cm1 and 1310, 1236, 1179, 1160 and 1154 cm1 are assigned to CAH in plane bending vibrations for aromatic ring show good agreement with computed wavenumbers at 1328, 1221, 1145, 1135, 1111 and 1077 cm1 by B3LYP/6-31G(d,p) method. The medium band observed in FTIR spectrum at 850 cm1 is assigned to CAH out of plane bending vibration show good agreement with computed wave number at 890 cm1 the PED corresponding to this vibration is a pure mode of contributing to 83%. NAH vibrations It has been observed that the presence of NAH vibrations in molecules may be correlated with a constant occurrence of absorption bands whose positions are slightly altered from one compound to another. In all the hetero cyclic compounds the NAH stretching vibrations occur in the region 3500–3300 cm1 [27–29]. The position of absorption in this region depends upon the degree of hydrogen bonding and physical state of the sample. In the present investigation the NAH stretching vibrations have been found at 3424 cm1 in FTIR and at 3421 cm1 in FT Raman spectrum with the 99% of PED contribution. Theoretically computed NAH vibrations by B3LYP method of scaled values approximately coincides with experimental value. CAC vibrations The CAC aromatic stretching vibrations give rise to characteristic bands in both the observed FTIR and FT Raman spectra, covering the spectral range from 1600 to 1400 cm1 [30]. In the present work CAC stretching vibrations are found at 1587, 1542, 1510, 1455 and 1410 cm1 in FTIR and three bands assigned at 1590, 1516, 1468 and 1450 cm1 in FT Raman spectra respectively. The calculated bands at B3LYP and HF levels in the same region are in excellent agreement with experimental observations of both in FTIR and FT Raman spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide. The ring in plane vibrations has given rise to weak bands across the low frequency region, that is to say, below 1000 cm1 [31]. The bands at 736, 676 and 640 cm1 have been assigned to CAC in plane bending vibrations. As is seen from (Table 3) the predicated frequencies by both RHF and B3LYP agree well with the observed ones with 85%, 80%, 78%, 28%, 44% and 36% of PED contributions. CAS vibrations It is difficult to the CAS stretching vibration for different compounds. Since it is of variable intensity and may be found over

CAN vibrations The identification of CAN vibration is a very difficult task, since the mixing of several bands is possible in the region Silverstein et al. [33] assigned CAN stretching absorption in the region 1342–1066 cm1 for aromatic amines. In this study, the bands identified at 1339, 1188 and 1034 cm1 in FTIR spectra and at 1325, 1179 and 1038 cm1 in FT Raman spectra have been assigned to CAN stretching vibrations. The theoretically scaled wave numbers at 1303, 1145, 1062 cm1 by B3LYP/6-31G(d,p) method corresponds to CAN stretching vibrations with PED of 36%, 16%, 55% and 67% respectively. SO2 Vibrations In solid phase, sulfonamides have a strong broad absorption band at 1360–1315 cm1 due to the asymmetric stretching vibration of the S@O group, where as the symmetric stretching vibration of this group shows the occurrence at 1280–1240 cm1 [34]. Similarly, in case of dilute solutions in non polar solvents, all organic sulfonamides have two strong bands at 1360–1290 cm1 and 1270–1220 cm1 due to asymmetric and symmetric stretching vibrations respectively. In the present case the FTIR spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide, shows the presence of the bands due to asymmetric and symmetric stretching of the S@O group at and 1339, 1248 and 1188 cm1 in FT Raman 1325, 1236 and 1160 cm1 contribution of 96%, 40% and 45% respectively. Other molecular properties NBO analysis NBO analysis provides the most accurate possible ‘natural Lewis structure’ picture of u, because all the orbital details are mathematically chosen to include the highest possible percentage of the electron density. A useful aspect of the NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra and inter-molecular interactions. The second-order Fock matrix was carried out to evaluate the donor–acceptor interactions in NBO analysis [35]. The interactions result is the loss of occupancy from the localized NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E2 associated with the delocalization i ? j is estimated as

E2 ¼ DEij ¼

qi ðF ij Þ2 ej  ei

where qi is the donor orbital occupancy, ej and ei are diagonal elements and Fij is the off diagonal NBO Fock matrix element Natural bond orbital analysis provides an efficient method for studying intra and intermolecular bonding and interaction among bonds, and provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital and the interacting stabilization energy resulting from the second order micro disturbance theory are reported [36,37]. The larger E2 value, more intensive is the interaction between electron donors and electron acceptors, i.e., the more donating tendency from electron donors to electron

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Table 2 Vibrational wave numbers obtained for 1,2-benzoxazol-3-ylmenthane sulfonamide at HF/6-31G(d,p) and B3LYP/6-31G(d,p) [harmonic frequency cm1], IR intensities (km mol1), Raman intensities (arb. units). Mode No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Experimental (cm1)

Calculated (cm1) (scaled)

HF/6-31G(d,p)

B3LYP/6-31G(d,p)

FTIR

FT-Raman

HFa

B3LYPa

IIRb

IRamanc

IIRb

IRamanc

3456(vw) 3424(vw) 3178(m) 3167(m) 3100(w) 2992(w) – 2967(vw) 1587(w) 1542(m) 1510(m) – 1455(s) 1410(s) 1389(vw) 1383(m) – 1339(m) 1316(m) 1309(vw) 1248(vw) 1188(vw) – 1157(w) 1062(w) 1034(ms) 1019(vw) – 984(vw) 937(s) 916(s) 895(vs) 850(w) 842(vw) 822(vs) 798(vs) – 736(s) 702(s) 676(ms) 658(s) 640(s) 572(s) 539(w) – – 455(s) 440(w) – – – – – – – – – – – –

– 3421(w) 3185(s) – – 2989(w) 2980(s) 2941(s) 1590(w) – 1516(ms) 1468(s) 1450(s) – 1377(w) 1362(m) 1348(s) 1325(w) – 1310(m) 1236(m) 1160(s) 1179(s) 1154(vw) – 1038(ms) 1029(vw) 1018 (vw) 988(vw) – 919(s) – – – 820(w) 789(w) 769(vw) – 705(s) 660(w) 654(w) 630(s) 570(s) 547(w) 492(ms) 486(m) 459(ms) – 436(w) 400(w) 362(w) 335(w) 307(w) 235(w) 211(ms) 178(w) 143(vw) 123(vw) – –

3549 3427 3066 3063 3045 3029 2993 2930 1649 1639 1597 1566 1490 1455 1428 1373 1352 1293 1278 1262 1243 1170 1136 1120 1106 1075 1057 1027 1013 994 982 925 882 876 867 796 777 770 752 738 662 591 563 552 523 492 461 448 441 429 358 328 281 241 223 186 159 72 62 26

3505 3389 3111 3105 3086 3071 3042 2969 1602 1587 1529 1507 1468 1419 1399 1357 1346 1303 1259 1328 1221 1145 1135 1111 1077 1062 1041 997 955 928 922 890 859 843 839 766 748 740 733 699 627 600 580 551 518 497 448 439 421 371 337 297 260 221 192 157 133 76 61 31

85 58 4 55 14 6 0 1 42 41 13 67 7 23 23 107 244 43 6 10 15 64 85 55 25 10 1 74 0 5 2 50 26 6 57 6 20 81 26 8 43 6 68 143 8 109 3 15 153 0 2 5 18 11 4 9 7 4 14 6

37 66 185 51 123 68 57 82 26 29 41 2 3 6 12 24 4 4 35 20 11 3 21 6 5 6 3 7 1 11 1 1 2 3 9 4 12 1 5 9 3 4 2 5 4 3 0 2 2 1 2 1 1 2 2 2 3 3 2 2

48 47 2 4 13 4 1 2 25 3 45 22 2 13 20 44 3 192 11 20 19 6 10 10 123 21 5 6 0 34 3 36 56 57 11 13 13 48 7 5 20 180 4 4 3 77 2 17 1 1 1 5 7 1 8 4 32 3 4 2

58 104 120 131 148 74 59 93 23 15 6 54 9 16 14 27 15 1 6 31 14 2 3 15 27 4 5 17 0 4 1 1 5 9 2 7 14 3 4 14 11 5 4 0 6 5 1 3 1 2 4 3 2 2 1 2 3 1 5 2

Vibrational assignments with PED (%)

NH2t(99) NH2t(99) (CAH)t(94) (CAH)t(96) (CAH)t(92) (CAH)t(98) (CAH)t(94) (CAH)t(97) (CAC)t(85) (CAC)t(85) (CAC)t(80) (CAC)t(78) (CAC)t(78) (CAC)t(80) (NAO)t(83) (CAC)t(18), (CACAN)d(20) (HACANAC)s(18), d(CACAN) (20) (CAN)t(55), t(S@O)(96), d(OANAC)(7) (HACAC)d(76), (CAC)t(21) (HACAC)d(55), (CAC)t(22) (HACAC)d(20) + t(CAC)(22) + (S@O)t(40) (HACAC)d(76), t(CAN)(36), (S@O)t(45) (HACAC)d(39), t(CAN)(36) (HANAC)d(16), (OANAC)d(7) (CAC)t(33), (CAO)t(12) (CACAC)d(33), (CAC) t(19), (CAN)t(16) (CAC)t(25), (CAO)t(15) (CAO)t(12), (CAHAH)s(10) (CACAO)x(10), (CAC)t(16), NH2 q(60) (HACACAN)s(72), (CACAN) d(53) (CAH)b(26), (CAC)t(13) (CACAC)d(67) (NAC)t(22) (CACAC)d(64) (CACAN)d(10), (CAH)x(51) (CAC)t(18), (HACAC)x(10) (CACAN)d(23) (HACACAC)s(17), (CAH)x(80), (CACAC) d(44) (CAS)m(12) (CACAC)d(26) (NAH)b(28) + (OAS)t(36) (CACAC)d(36) (CANAHAH)r(27), (HACAC)d(42) (CANAHAH)r(24), (CACAC)s(15) (CAHAH)s(26), (CACAC)s(17), (CACA0) s(10) (CACAC)d(51) (CAHAH)s(16) (CACAC)d(28), (NAH)x(62) (CACAC)d(30) (CACAN)d(16) (HAOACAC)s(52) (CACAC)d(20) (CACAC)r(18) (OAC)t(19) + (CACACAC)s(10) (HACACAC)s(16), (CACAC)d(11) (CACAN)t(42), (CACAH)s(11) (CACAS)s(18), (CAACAH)s(11) (CANACAC)s(38), (CACAC)r(16) (CANACAC)s(32), (CACAC)r(16) (CACACAC)s(64)

Abbreviations: s-strong; vs-very strong; ms-medium strong; w-weak; vw-very weak; m-stretching; b-bending; r-out of plane bending; s-torsion; d-inplane bending; qrocking; x-wagging. a Scaling factor; 0.961 for B3LYP/6-31G(d,p) and 0.903 for HF/6-31G(d,p). b Relative absorption intensities normalized with highest peak absorption equal to 100. c Relative Raman intensities normalized to 100.

acceptors and the greater the extent of conjugation of the whole system. Delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO orbitals and formally unoccupied (antibond or Rydgberg) non Lewis NBO orbitals correspond to

a stabilizing donor acceptor interaction. NBO analysis has been performed on the molecule at the B3LYP/6-31G(d,p) level in order to elucidate the intra-molecular, re-hybridization and delocalization of electron density within the molecule. The intra-molecular

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S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 603–613 Table 3 Second order perturbation theory analysis of Fock matrix in NBO basis for 1,2-benzoxazol-3-ylmenthane sulfonamide. Donor (i)

a b c

Type

ED/e

Acceptor (j)

Type

ED/e

a

E(2) (kJ/mol)

b

E(j)  E(i) (a.u)

c

F(i, j) (a.u)

C1AC4

r

1.972

C1AH15 C1AH16 O2AN3 N3AC4

r r r r

0.008 0.010 0.042 0.017

0.83 0.73 5.32 3.40

1.15 1.53 1.19 1.88

0.032 0.030 0.071 0.071

C1AS11

p

1.969

N3AC4 S11AO12 S11AO13 S11AN14

p p p p

0.017 0.088 0.109 0.180

5.68 4.25 4.67 4.64

1.84 1.49 1.48 1.23

0.092 0.072 0.076 0.070

C1AH15

p

1.972

N3AC4 C4AC5

p p

0.231 0.035

5.51 3.85

0.94 1.05

0.068 0.059

C1AH16

r

1.975

C4AC5 S11AO13

r r

0.035 0.109

2.65 3.23

1.68 1.30

0.060 0.059

O2AN3

r

1.963

C1AC4 C5A C6 C4AC10

r r r

0.028 0.042 0.028

10.03 3.50 13.53

1.35 1.70 1.73

0.106 0.069 0.137

O2AC6

p

1.993

C5AC7

p

0.030

3.60

2.36

0.083

C6AC10 C9AC10

p p

0.028 0.015

3.90 1.02

2.34 2.36

0.086 0.044



N11AC4

r

1.961

C4AC5 C5AC7 C5AC6

r r r

0.035 0.030 0.452

5.20 5.66 9.16

2.16 2.21 0.69

0.095 0.100 0.080

O2

LP(1)

1.999

C5AC6 N3AC4

r r

0.042 0.017

7.30 1.31

1.79 1.76

0.103 0.043

N3 O12 O12 O13 N14

LP(1) LP(2) LP(2) LP(3) LP(1)

1.992 1.854 1.854 1.975 1.933

C4AC5 S11AO13 S11AN14 S11AN14 C7AH17 S7AO13 S11AO12

r r r r r r r

0.231 0.109 0.180 0.180 0.074 0.109 0.088

6.44 29.04 14.43 35.35 15.96 6.13 1.44

1.62 1.00 0.75 0.74 1.36 1.12 1.13

0.092 0.154 0.094 0.143 0.132 0.075 0.036

E(2) means energy of hyper conjugative interaction (stabilization energy). E(j)  E(i) Energy difference between donor and acceptor i and j NBO orbital’s. F(i, j) is the Fock matrix element between i and j NBO orbital’s.

interaction is formed by the orbital overlap between r(CAC) and r(CAC) bond orbital which results intra-molecular charge transfer (ICT) causing stabilization of the system. These interactions are observed as increase in electron density (ED) in CAC antibonding orbital that weakens the respective bonds [38]. The electron density of conjugated double as well as single bond of the aromatic ring (1.9e) clearly demonstrates strong delocalization the most important interaction energy in this molecule is electron donating from O2 LP(1) to the antibonding (C5AC6) resulting stabilization of 7.30 kJ/mol. The same O12 LP(2) with (S11AO13) leads to a strong stabilization of 29.04 kJ/mol. The same O13 LP(3) with (S11AN14) leads to more strong stabilization of 35.35 kJ/mol. NBO analysis clearly manifests the evidences of the intra-molecular charge transfer from r(C1AC4) to r(O2AN3) antibonding orbital’s as shown in Table 4 that clearly shows large stabilization energy 5.32 kJ/mol. In the case of p(C1AS11) orbital’s the p(S11AO12) and (S11AO13) show stabilization energy of 4.25 and 4.67 kJ/mol.

Mulliken population analysis The Mulliken atomic charges are calculated by determining the electron population of each atom as defined by the basis function [39]. The Mulliken atomic charges of 1,2-benzoxazol-3-ylmenthane sulfonamide molecule are calculated by HF and B3LYP method with 6-31G(d,p) basis set. Calculation of effective atomic charges plays an important role in the application of quantum chemical calculations to molecular systems. Our interest here is in the comparison of different methods to describe the electron distribution in 1,2-benzoxazol-3-ylmenthane sulfonamide as broadly as possible, and assess the sensitivity, the calculated charges to changes in (i) the choice of the basis set; (ii) the choice of the quantum mechanical method. Mulliken charges, calculated the electron population of each atom defined in the basic functions. The Mulliken charge calculated different levels and at same basis set listed in supplementary Table S2. The nitrogen atoms N3 and N14 have more negative charges where as all the hydrogen atoms

Table 4 The UV–vis excitation energy E (eV) and oscillator strength (f) for 1,2-benzoxazol-3-ylmenthane sulfonamide calculated by TD-DFT/B3LYP method. Method

TD

States

S1 S2 S3

kobs (nm)

283.0 238.0 214.0

B3LYP/6-31G(d,p) kcal (nm)

Excitation energy (eV)

Oscillator strength (f)

304.37 269.13 265.76

4.073 4.606 4.665

0.0011 0.0007 0.0768

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LUMO Plot (first excited state) LUMO energy = 5.3696 eV

Energy Gap (ΔΕ) = 6.2608 eV

HOMO energy = -0.8912eV HOMO Plot (ground state)

as can be seen through the UV–vis spectra absorption values (283, 238 and 214 nm). A band may be appear due to electron transition of the ring 2 to ring 1 through bridge transition of (p–p). The calculated results shows the vertical excitation energies, oscillator strength (f) and wavelength of the molecule. These values are compared with the experimental wavelength. TD-DFT (B3LYP) with 6-31 G(d,p) predict one intense electronic transition at 4.073 eV (304.37 nm) with an oscillator strength f = 0.0011, in good agreement with the measured experimental data [kexp = 238 nm] as shown in Fig. 3. The frontier molecular orbital plays an important role in the electric and optical properties, as well as in the UV–vis spectra and chemical reaction [40,41]. Fig. 5 shows that the frontier molecular orbital of HOMO and LUMO computed by B3LYP/6-31G(d,p) level. Both the highest occupied molecular orbital’s (HOMOs) and the lowest unoccupied molecular orbital’s (LUMOs) are mainly localized on the rings which indicates that HOMO–LUMO is mostly the anti-bonding type orbitals. The value of the energy separation between the HOMO and LUMO is E = 6.2608 eV. Total, partial, and overlap population density-of-states

Fig. 5. The atomic orbital compositions of the frontier molecular orbital for 1,2benzoxazol-3-ylmethane sulfonamide.

have a positive charge. The maximum atomic charge is obtained for C5 and C6. The minimum atomic charge is obtained for C4 when compared with other atoms. The maximum charge is due to the attachment of negatively charged oxygen atoms O12 and O13. UV–vis spectra analysis Ultra–violet spectra analyses of 1,2-benzoxazol-3-ylmenthane sulfonamide have been investigated by TD-DFT/B3LYP/6-31G(d,p) method. The theoretical wave length of (kmax) are a function of the electron availability which have been reported in Table 4. The calculations of molecular orbital geometry shows that the absorption maxima of this molecule. The electronic transition between frontier orbitals such as translation from HOMO to LUMO

Consideration of only the HOMO and LUMO may not yield a realistic description of the frontier orbitals, because in the boundary region, neighboring orbitals may show quasi degenerate energy levels. For this reason, the total (TDOS), partial (PDOS), and overlap population (OPDOS or COOP (Crystal Orbital Overlap Population)) density of states, in terms of Mulliken population analysis are calculated and created by convoluting the molecular orbital information with Gaussian curves of unit height and full width at half maximum (FWHM) of 0.3 eV by using the Gauss Sum 2.2 program [42]. Figs. 6–8 represent the TDOS, PDOS and OPDOS plot of 1,2benzoxazol-3-ylmenthane sulfonamide molecule, respectively. The most important application of the DOS plots is to demonstrate MO compositions and their contributions to the chemical bonding through the OPDOS plots, which are also referred in the literature as COOP diagrams. The bonding, antibonding and nonbonding natures of the interaction of the two orbitals, atoms or groups are shown by OPDOS diagram. A positive value of the OPDOS indicates

Fig. 6. The calculated TDOS diagram of 1,2-benzoxazol-3-ylmenthane sulfonamide.

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 603–613

a bonding interaction (because of the positive overlap population), negative value means that there is an anti-bonding interaction (due to negative overlap population) and zero value indicates nonbonding interactions. Additionally, the OPDOS diagrams allow us to determine and compare of the donor–acceptor properties of the legends and ascertain the bonding and non-bonding. The calculated total electronic density of states (TDOSs) diagrams of the 1,2-benzoxazol-3-ylmenthane sulfonamide is given in Fig. 6. The partial density of state plot (PDOS) mainly presents the composition of the fragment orbitals contributing to the molecular orbitals which is seen from Fig. 7.

611

Thermodynamic properties Entropy of the title compound is presented in supplementary Table S3 scaled factors have been recommended for an accurate prediction in determining the zero-point vibration energies (ZPVE) and the entropy Svib (T) [43]. The variation in the ZPVE’s seemed to be in significant, the total energies and the changes in the total energy of 1,2-benzoxazol-3-ylmenthane sulfonamide at room temperature at different methods are also presented. The biggest value of ZPVE of 1,2-benzoxazol-3-ylmenthane sulfonamide is 109.06 kcal/mol obtained and HF/6-31G(d,p) where as the smallest

Fig. 7. The calculated PDOS diagram of 1,2-benzoxazol-3-ylmenthane sulfonamide.

Fig. 8. The calculated OPDOS diagram of 1,2-benzoxazol-3-ylmenthane sulfonamide.

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S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 603–613

Fig. 9. Correlation graphs of thermodynamic properties at different temperaturefor1,2-benzoxazol-3-ylmenthane sulfonamide.

value are 103.82 kcal/mol obtained at B3LYP/6-31G(d,p). Dipole moment is a measure the symmetry in the molecular charge distribution and is given as a vector in the three dimensions. The values of dipole moment and energies for 1,2-benzoxazol-3-ylmenthane sulfonamide molecule were also calculated in supplementary Table S3. According to HF and B3LYP calculations the largest dipole moment were observed for B3LYPand increase in the energy were observed for HF. On the basis of vibrational analysis, the statically thermodynamic functions: heat capacity (C 0p;m ), entropy (S0m ), and enthalpy changes (DH0m ) for the title molecule are obtained from the theoretical harmonic frequencies and listed in supplementary Table S4. From supplementary Table S4, it can be observed that these thermodynamic functions are increased with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures are fitted by quadratic formulas and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9541, 0.9999 and 0.9995, respectively. The corresponding fitting equations are as follows and the correlation graphics of those shown in Fig. 9.

bond lengths are concerned, both the methods have performed nearly to the same level across the bond angle sets. Potential Energy Distributions (PED) suggest that several normal modes are coupled in varying degrees. The electric dipole moment, polarizabilities and the hyperpolarizabilities of the compound studied that have been calculated by HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods. NBO result 1,2-benzoxazol-3-ylmenthane sulfonamide reflects the charge transfer mainly due to CAC group. It could be concluded that population analyses is suitable for the estimation of the changes of the atomic charges. The theoretical TD-DFT/B3LYP/6-31G(d,p) calculated results also complements with measured UV–vis spectral data’s. The HOMO and LUMO energy gap reveals that the energy gap reflects the chemical activity of the molecule. Orbital energy interactions between selective functional groups are analyzed by density of energy states. Thermodynamic properties in the range from 100 to 1000 K are obtained. The gradients of C 0p and S0m to the temperature decreases, but that of DH0m increases, as the temperature increases. This study demonstrates that scaled HF and B3LYP calculations are powerful approaches for understanding the vibrational spectra of 1,2-benzoxazol-3-ylmenthane sulfonamide.

C 0p;m ¼ 11:4363 þ 0:7409T  3:3706  104 T 2 ðR2 ¼ 0:9541Þ

Appendix A. Supplementary material

S0m ¼ 240:4821 þ 0:7979T  1:9707  104 T 2 ðR2 ¼ 0:9999Þ H0m ¼ 9:8650 þ 0:0996T þ 1:8433  104 T 2 ðR2 ¼ 0:9995Þ All the thermodynamic data supply helpful information for the further study on the 1,2-benzoxazol-3-ylmenthane sulfonamide. They can be used to compute the other thermodynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermo chemical field [44]. Notice: all thermodynamic calculations are done in gas phase and they could not be used in solution. Conclusions A complete vibrational frequency assignments of 1,2-benzoxazol-3-ylmenthane sulfonamide has been carried out using FTIR and FT-Raman spectrum. The equilibrium geometries, harmonic vibrational frequencies, IR intensities of the title compound were determined and analyzed by HF and B3LYP levels of theory utilizing 6-31G(d,p) basis set. The observed and calculated fundamental frequencies by HF and B3LYP has performed better than HF as far as the

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