Spectroscopic (FTIR, FT-Raman, UV and NMR) investigation and NLO, HOMO–LUMO, NBO analysis of 2-Benzylpyridine based on quantum chemical calculations

Accepted Manuscript Spectroscopic (FTIR, FT-Raman, UV and NMR) investigation and nlo, homolumo, nbo analysis of 2-benzyl pyridine based on quantum chemical calculations R. Mathammal, N. Sudha, L. Guru Prasad, N. Ganga, V. Krishnakumar PII: DOI: Reference:

S1386-1425(14)01290-6 http://dx.doi.org/10.1016/j.saa.2014.08.099 SAA 12620

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

17 June 2014 30 July 2014 24 August 2014

Please cite this article as: R. Mathammal, N. Sudha, L. Guru Prasad, N. Ganga, V. Krishnakumar, Spectroscopic (FTIR, FT-Raman, UV and NMR) investigation and nlo, homo-lumo, nbo analysis of 2-benzyl pyridine based on quantum chemical calculations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.08.099

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SPECTROSCOPIC (FTIR, FT-RAMAN, UV AND NMR) INVESTIGATION AND NLO, HOMO-LUMO, NBO ANALYSIS OF 2-BENZYL PYRIDINE BASED ON QUANTUM CHEMICAL CALCULATIONS R. Mathammala*, N. Sudhaa, L. Guru Prasadb N. Gangaa, V. Krishnakumarc a

Department of Physics, Sri Sarada College for Women (Autonomous), Salem, Tamilnadu, India. b

Department of Physics M.Kumarasamy College of Engineering Karur,Tamilnadu, India c

Department of Physics, Periyar University , Salem, Tamilnadu, India.

Abstract In this work, the vibrational characteristics of 2-Benzylpyridine have been investigated. Thestructure of the molecule has been optimized and the structural characteristics of the molecule have been determined by density functional theory B3LYP method with 6-31G(d,p) basis set. The infrared and Raman spectra have been simulated from calculated intensities. Both the experimental and theoretical vibrational data confirms the presence of functional groups in the title compound. The 1H and

13

C NMR spectra were recorded and 1H and

13

C nuclear

magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital method. UV-Visible spectrum of the title compound was recorded in the region 190-1100 nm and the electronic properties HOMO and LUMO energies were calculated by CIS approach.Nonlinear optical and thermodynamic properties were interpreted. All the calculated results were compared with the available experimental data of the title molecule. Keywords: FT IR, FT-Raman, NMR, DFT, NLO, NBO. * Corresponding author Tel. +91 427 2447664 E-mail: [email protected]

1

1. INTRODUCTION Molecular organic compounds with one or more aromatic system in a conjugated position leading to charge transfer. The substituted benzene derivatives with high optical nonlinearity are very promising materials for future optoelectronic and nonlinear optical applications [1]. Moreover benzene derivatives are widely used to manufacture therapeutic chemicals, dyes, artificial leather and detergent products. The substituents on a benzene ring can influence the reactivity. Inclusion of substituents in the benzene molecule leads to the variation of charge distribution in the molecule and consequently the structural, electronic and vibrational parameters get affected. Pyridine is a basic heterocyclic organic compound. It is a used as a precursor to agrochemicals and pharmaceuticals and it is also used as solvent in manufacturing of dyes and rubber [2]. It is produced from coal tar, aby-product of coal gasification. Pyridine is an important raw material in the chemical industry. It is added to foods to give them a bitter flavour. Many substituted pyridines are involved

in bioactivities withapplications in

pharmaceutical drugs and agricultural products[3,4]. Pyridine derivatives are used as prodrugs for treating neuronaldamage caused by stroke to name a few. They also underpin analgesicsfor acute and chronic pain, treatment for tinnitus, depressionand even diabetic neuropathy. Pyridine derivatives have also been used as nonlinear materials andphoto chemicals. Some of these crystals have been reported as frequencyconverters from NIR to the visible wavelength region [5]. Theharmonic frequencies of pyridine derivatives were calculated byseveral authors [6,7].Many works have been found in the literature dealing with thevibrational analysis of pyridine [8-11]. The vibrational spectroscopy serves as the major tool for the identification and structural elucidation of any compound. The present study aims at elucidating the structure and vibrational frequencies of 2-Benzylpyridine based on density functional theory calculations. The vibrational spectral properties of 2-Benzylpyridine is completely calculated at DFT levels using 6-31G(d, p) basis set to identify various normal modes with greater accuracy. The density functional theory calculations are reported to provide accurate vibrational frequencies which are scaled to compensate for the approximate treatment of electron correlation, for basis set deficiencies and for the anharmonicity. To the best of our knowledge, neither quantum chemical calculations nor 2

the vibrational spectra have been reported as yet. This inadequacy observed in the literature encouraged us to make this theoretical and experimental vibrational spectroscopic research based on the structure of molecules to give a correct assignment of the fundamental bands. The entire scaled quantum mechanical method and density force field calculations are performed by combining the experimental and theoretical aspects of Pulay and Raghut [12]. 2. EXPERIMENTAL DETAILS The compound 2-Benzylpyridine (2BP) in the liquid form is purchased from Sigma Aldrich chemical company, Chennai with the purity of 98% and used as without further purification. FTIR spectrum of the compound was recorded in the 4000-400 cm-1 region at a resolution of

2cm-1 using a Perkin-Elmer Spectrometer. The FT-Raman spectrum of the

compound was recorded in the frequency region 50-4000 cm-1 using BRUKER RFS27 Spectrometer. The UV-Vis spectrum has been recorded using a Perkin-Elmer Lambda 35 Spectrophotometer in the range of 190-1100nm at a scanning speed of 960nm/min.The 1H and 13

C NMR spectra were recorded on Brucker DPX 400 MHz FT-NMR spectrometer, DMSO was

used as a solvent. 3. COMPUTATIONAL DETAILS All the computational calculations were performed using Gaussian 09 program [13] and the output files were visualized by means of the Gauss view 05 software. The optimized structure and vibrational spectra of 2-Benzylpyridine were determined by using B3LYP (Becke’s three parameter hybrid model using the Lee-Yang Parr correlation functional) [14,15]. The optimized structural parameters have been evaluated for the calculations of vibrational frequencies by assuming C1point group symmetry. In the optimized geometry no imaginary frequencies were obtained, therefore there is a true minimum on the potential energy surface. As a result, the unscaled calculated frequencies, infrared intensities, Raman activities and depolarization ratios were obtained. In order to fit the theoretical wavenumbers to the experimental, the scaling factors have been introduced by using a least square optimization. Vibrational frequencies were scaled as 0.956 for all vibration modes. After scaling with the scaling factor, the deviation from the experiments is less than 10 cm-1 with a few exceptions. The assignments of the calculated normal modes have been made on the basis of the corresponding PEDs. The PEDs were computed from the quantum chemically calculated vibrational frequencies using VEDA4 program [16]. The 3

electronic absorption spectra for optimized molecule was calculated with the CIS at B3LYP/631G (d, p) level in gas phase. Furthermore, the dipole moment, linear polarizability and first hyperpolarizability and Mulliken Atomic charges were also obtained for the title molecule. The frontier molecular orbital energies, energy gap between various occupied and unoccupied molecular orbitals of 2-Benzylpyridine were also calculated in the

B3LYP/6-31G (d, p)

level. Moreover the changes in the thermodynamic functions (the heat capacity, entropy and enthalpy) were investigated for the different temperatures from the vibrational frequency calculations of title molecules. NBO calculation is also performed on the 2-Benzylpyridine with the same level of DFT theory with 6-31G (d, p) basis set. The 1H NMR and

13

C NMR(Nuclear

Magnetic Resonance) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. 4. Results and Discussion 4.1 Molecular geometry The molecular structure along with the numbering of atoms of 2BP was obtained from Gaussian 09 and Gaussview programs and is shown in Fig. 1. The Global minimum energy obtained by the DFT structure optimization of 2BP was found to be -518.6677Hartrees. The most optimized structural parameters(bond length and bond angle) calculated by DFT/ B3LYP with 6-31G(d,p) basis set are shown in the Table. S1.The title compound belongs to C1 point group symmetry with 24 atoms. From the Table. S1 the bond lengths of C-C are ranging from 1.39-1.52Å, C-N bonds are ranging from1.33-1.34Å and the C-H bond lengths are ranging from1.08-1.09Å. The bond angles are same for all atoms but the methylene group bond angles are slightly varied. The bond angles of CCC, CCN and CCH are in the range from 118-124º and the methylene group bond angles are ranging from 107-109°. While the methylene group is attached near to the electronegative nitrogen atom. So the bond length and bond angles of the methylene are decreased compared to the others.Comparing the theoretical data with the experimental results indicate that optimized bond lengths and bond angle values are slightly different from these of the experimental ones. This small discrepancy originate from that the theoretical calculations are performed for isolated molecule in gas phase whereas the experimental data belong to solid-phase. It should be noted

4

that the geometry of the solid state structure is subject to intermolecular interactions such as VanderWaals interactions [17, 18] 4.2 Vibrational analysis The goal of the vibrational analysis is to find vibrational modes connected with molecular structure of investigated compound. The numerical harmonic vibrational analysis was done for the optimized geometry. Vibrational spectra assignments were performed on the recorded FTIR and FT Raman spectrum based on theoretically predicted wavenumbers and PED. The observed, selected and calculated wavenumbers along with their relative Raman activity, IR intensity and probable assignment with PED of title molecule are given in the Table. 1. It should be noted that the calculations were made for a free molecule in vacuum, while the experiment was performed for liquid samples. Furthermore, the anharmonicity is neglected in the real system for the calculated vibrations. Therefore there are disagreements between calculated and observed vibrational wavenumbers and because of the low IR intensities of some modes. The observed and stimulated FTIRand FT Raman spectra are depicted in Figs 2& 3. The existence of one or more aromatic rings in a structure is normally readily determined from the C-H and C-C vibrations. In present study, a satisfactory vibrational band assignment has been ascertained for the title compound in terms of normal modes of vibration using FTRaman and FT-IR spectroscopy. The optimized molecular conformation exhibits no special symmetries.The discrepancies are taken care of either by computing anharmonic corrections explicitly or by introducing scalar field or even by direct scaling of the calculated wavenumbers with a proper scaling factor. The comparison of the scaled wavenumbers with experimental values reveals that the B3LYP shows very good agreement with the experimentally observed spectra.DFT method predicts vibrational spectra with high accuracy and is applicable to a large number of compounds. Ring C-C vibrations The bands between 1450 and 1650 cm−1 are within theC–C stretching modes [19]. In the present study, the carbonstretching vibrations of the title compound were observed at 1449, 1471, 1556, 1569, 1573, 1588 cm-1. Some wavenumbers are observed in the out of range because

5

the presence of the electronegative atom of nitrogen. The in plane and out-of-plane bending vibrations of C–C are presented in Table. 2. Theseassignments are in good agreement with literature and calculated wavenumbers [20]. C-H vibrations The existence of one or more aromatic rings in a structure is normally readily determined from the C-H vibrations. The substituted benzene like molecule gives rise to C-H stretching, C-H in-plane bending and out-of-planebending vibrations. The aromatic structure shows the presence of C-H stretching vibrations in the region 3100-3000cm-1 which is the characteristic region for the ready identification of C-H stretching vibrations. In the region, the bands are not affected appreciably by the nature of substituent. This mode is calculated in the range 3070-3023 cm-1. The C-H in-plane bending frequencies appear in the range 1100-1400 cm-1 and are very useful for characterization purpose. In this work, the in-plane-bending vibrations were observed in the range of 1253-1431cm-1. The C-H out-of-plane bending vibrations were strongly coupled vibrations and occur in the region 1000-750 cm-1[21]. In this work the out-of-plane bending vibrations were recorded in the range of 820-978 cm-1. These vibrations were mostly present at the out of range while the electronegative nitrogen and methylene group are present in the title molecule. Methylene vibrations One methylene group is attached to the benzene ring in our title compound. The spectral position of C-H stretching of the methylene group is at lower frequencies than those of the C-H stretching. The anti-symmetric stretching vibrations are generally observed in the region 30002900cm-1. The C-H stretching vibrations are generally observed at 2923, 2970 cm-1[22,23]. The C-H in plane bending vibrations are generally occur near 1000 cm-1, and the out-of-plane bending vibration near the region of 750cm-1, for the title compound, the methylene group were present in the centre of benzene and pyridine group. So the in plane bending vibrations and outof plane bending vibrations are deviated from literature values.

6

C-N vibrations Silverstein and Webster assigned the C-N stretching vibrations in the region 13821266cm-1.In our compound, the C-N stretching vibrations were observed at 1281, 1311cm-1. Many of these vibrations are vibrated at the out of region, the pyridine ring is substituted in the methyl group, and the atoms are having different electro negativities, so the bonding electrons are not equally distributed between the two atoms. So the vibrations vary from theoretical value. The in plane C-N bending and out-of-plane bending vibrations were calculated at 1400-963cm-1 and 867-234cm-1 for the B3LYP level. 4.3 1H and 13C NMR spectral analysis NMR spectroscopy is currently used for structure and functional determination of biological macromolecules [24]. Chemical shifts are recognized as an imperative part of the information contained in NMR spectra. They are valuable for structural interpretation due to their sensitivity to conformational variations. The combined use of NMR and computer simulation methods offers a powerful way to interpret and predict the structure of large biomolecules. The isotropic chemical shifts are frequently used as an aid in identification of reactive organic as well as ionic species. It is recognized that the accurate predictions of molecular geometries are essential for reliable calculations of magnetic properties. Therefore full geometry optimization of 2BP was performed at DFT B3LYP / 6-31G (d, p) method. Then Gauge-Independent Atomic orbital 1H and 13C NMR chemical shift calculations of the 2BP have been made by sample method. The1H and

13

C NMR chemical shifts were recorded in DMSO. The results are

summarized in Table S2 & S3 shows the range NMR chemical shift of typical organic molecule is usually > 100.The aromatic carbons generally give signals in the range of 100-150 ppm. In the present study, signals for aromatic carbons were observed at 123-156 ppm. But the greater chemical shift 165.4617ppm corresponds to C5. While the carbon is present near the electronegative Nitrogen atom, the peak at 54.0013 ppm corresponds to methylene group. Methylene is an electron releasing group so the chemical shift can be decreased as shown in Fig. S1 (a) & S1(b).The signals of the aromatic proton were observed at 7-9 ppm. The methylene group hydrogen shows 4 ppm. H atom is the smallest of all atoms and mostly localized on periphery of molecules. Therefore their chemical shifts would be more susceptible to 7

intermolecular interactions in the aqueous solution as compared to that of other heavier atoms as shown in Fig. S2 (a) & S2 (b). 4.4. Electronic properties The electronic property says that the changes in electronic energy levels within the molecule arising due to transfer of electrons from π- or non-bonding orbitals. Electronic transitions are usually classified according to the orbitals engaged or to specific parts of the molecule involved. Common types of electronic transitions in organic compounds are * and

*(acceptor)

(donor).

–

*, n–

In order to explain the electronic transitions of 2BP

theoretical calculations on electronic absorption spectrum capable of describing the spectral features of the molecule, were performed by CIS method. The calculated two lowest-energy transitions of the molecule are observedin 215 and 256nm. These transitions are corresponding to π-π *. The transitions are good agreement with the experimental values. Peaks do not appear in the range 300-1100 nm so this molecule possesses a good NLO property. The theoretical and the experimental spectra are shown in the Fig. S3(a) & S3(b). The UV spectrum of 2BP measured is used to calculate group contributions to the molecular orbitals.The conjugated molecules are characterized by a highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) separation, which is the result of a significant degree of intermolecular charge transfer from the end-capping electron-donor to the efficient electron acceptor group through π-conjugated path. The strong charge transfer interaction through π-conjugated bridge results in substantial group state donor acceptor mixing and the appearance of a charge transfer band in the electronic absorption spectrum. Therefore, an electron density transfer occurs from the most aromatic part of the π-conjugated system in the electron-donor side to electron-withdrawing part. A deeper understanding of chemical reactivity can be gained by this electronic absorption correspond to the transition from the ground state to the excited state and it is mainly described by one electron excitation from the HOMO to the LUMO orbital. Molecular orbitals when viewed in a qualitative graphic representation can provide insight into the nature of reactivity and some of the structural and physical properties of molecules. Well known concepts such as conjugation, the lone pairs are well illustrated by molecular orbitals. Molecular orbital co-efficient analysis showed that the frontier molecular 8

orbital (FMOs) are composed mainly of π-atomic orbitals. Hence the electronic spectrum corresponding to electronic transitions are mainly π- π*. The dipole moment in a molecule is an important property that is mainly used to study the intermolecular interactions involving the nonbonded type dipole-dipole interactions, because higher the dipole moment stronger will be the intermolecular interactions. The energy levels of the HOMO and LUMO orbitals computed at the B3LYP / 6-31G (d, p) level for the title compound are represented in Fig. 4 & 5. The HOMO plot is localized on the benzene ring. In the pyridine ring HOMO plot is partially localized because of the nitrogen atom, the LUMO plot is localized on almost the whole molecule. The HOMO and LUMO plots shown in Fig.4 & 5 are mostly anti-bonding type orbitals.Gauss Sum2.2 program was used to calculate group contribution to the molecular orbitals (HOMO & LUMO) and prepare the density of the states (DOS) Fig.S4 shows population analysis per orbital and demonstrates a simple view of the character of the molecular orbitals in a certain energy range. The calculated energy value of HOMO and LUMO are -0.23387eV, -0.02393eV respectively. The energy gap between HOMO and LUMO indicates the molecular chemical stability. The energy gap between HOMO and LUMO is -0.20994eV. The energy gap is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity [25]. HOMO energy =-0.23387eV LUMO energy =-0.02393eV HOMO-LUMO= -0.20994eV The electronic properties of the molecules are calculated from the total energies and the Koopan’s theorem. The ionization potential is determined from the energy difference between the energy of the compound derived from electron-transfer and the respective neutral compound, IP=-EHOMO while the electron affinity is computed from the energy difference between the neutral molecule and the anion molecule. EA=-ELUMO respectively, the other important quantities such as electronegativity(χ), hardness(η), softness(ζ) and electrophilicity(ψ) were deduced from ionization potential and electron affinity values. Electronegativity (χ) =- χ=

9

Chemical hardness (η) = Softness (ζ) = Electrophilicity index (ψ) = The values of electronegativity, chemical hardness, softness and electrophilicity index are 0.1289, 0.105, 4.7619 and 0.0791 for the title molecule. In the HOMO-LUMO plot red phase are positive and the green phase are negative. 4.6 NLO properties Nonlinear optical effects arise from the interactions of the electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristic from the incident fields [26,27]. NLO is at the forefront of current research because of its importance in providing the key functions of frequency shifting, optical modulation, optical switching, optical logic and optical memory for the emerging technologies in area such as telecommunications, signal processing and optical interconnections [28]. Dipole moment is one of the important qualities which are of fundamental importance in structural chemistry. It can be used as a descriptor to illustrate the charge movement across the molecule. The first hyperpolarizability (β0) of this novel molecular system and the related properties of 2-Benzylpyridine are calculated using the B3LYP / 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. The first hyperpolarizability is a third-rank tensor that can be described by a 3X3X3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry. It can be given in the lower tetrahedral. The components of β are defined as the co-efficient 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: E=E0-µ αFα-½µ αβFαFβ-

βαβγFαFβFγ+……

Where E0 is the energy of the unperturbed molecule, Fα the field at the origin and µ α, µ αβ and βαβγ are the components of dipole moment, polarizability and the first hyperpolarizabilityrespectively.

10

The total static dipole moment (µ 1), polarizability (α1), mean polarizability (∆α) and the mean first hyperpolarizability (β0) using the x,y,z components are defined as follows: µ= (µ x 2+µ y2+µ z2)1/2 α= ( ) (αxx+αyy+αzz ) ∆α= 1/√2[(αxx-αyy)2+(αyy-αzz)2+(αzz-αxx)2+6αxz2+6αxy2+6αyz2]½ β0= [(βxxx+βxyy+βxzz)2+(βyyy+βyzz+βyxx)2+(βzzz+βzxx+βzyy)2] ½ Since the values of the αand β0 of the Gaussian 09 output are reported in atomic units (a.u). The calculated values have been converted in to electronic units (for α:1a.u= 0.1482X1024

esu; for β: 8.6393X10-33esu). The calculated value of dipole moment (µ) was found to be

3.2906 Debye. The highest value of dipole moment is observed for compound µ y. In this direction, this value is equal to -1.2324. The calculated polarizability and anisotropy of the polarizability2-Benzylpyridine is 17.9543X10-24 esu and 10.2941X10-24esu respectively. The magnitude of the molecular hyperpolarizabilityβ is one of the important key factors in a NLO system. The B3LYP / 6-31G (d, p) calculated first hyperpolarizability value of 2-Benzylpyridine is equal to 1017.7585X10-33esu. The dipole moment and first hyperpolarizability of the title molecule is approximately 2.396, 2.73 times than those of urea (the µ and β of Urea are 1.3732 D and 372.89X10-33esu) [29] obtained by B3LYP/6-31G (d, p) method. The large value of hyperpolarizabilityβ0, which is a measure of non-linear optical activity of the molecular system, is associated with the intra-molecular charge transferresulting from the electron cloud movement through π conjugated frame work from electron donor to electron acceptor groups. The predicted polarizability and first hyperpolarizability for the 2BP are shown in Table. 2. The physical properties of these conjugated molecules are governed by the high degree of electronic charge delocalization along the charge transfer axis and by the low band gaps. Therefore we conclude that the title molecule is an attractive object for future studies of non-linear optical properties. 4.7 NBO analysis: NBO provides an accurate method for studying interaction and also gives an efficient basis for investigating charge transfer or conjugative interaction in various molecular systems [30]. The large value of second order stabilization energy E (2) shows that the interaction is more intense between electron donors and electron acceptors, i.e., the more donating tendency from 11

electron donors to electron acceptors and the greater the extent of conjugation of the whole system. The delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO orbitals and formally unoccupied (antibond) non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor interaction. In order to characterize the intra and intermolecular interactions quantitatively, a second-order perturbation theory is applied that gives the energy lowering associated with such interactions. For each donor NBO(i) and acceptor NBO(j), the strength of various types of interactions or stabilization energy (E(2)) associated with electron delocalization between donor and acceptor is estimated by the second order energy lowering equation and it is described below [31, 32].

Whereqiis the population of donor orbital or donor orbital occupancy; εi, εjare orbital energies of donor and acceptor NBO orbitals, respectively; Fijis the off-diagonal Fock or Kohn–Sham matrix element between i and j NBO orbitals. Various intra and intermolecular interactions are generated due to the different types of ‘‘orbital–orbital’’/‘‘lone pair-orbital’’ overlap. The π conjugation and resonance due to π electron delocalization in ring is involved due to π→π* interactions, whereas the primary hyperconjugative interactions due to the various types of orbital overlaps such as σ→π*, π→σ* and secondary hyperconjugative interactions due to the σ→σ* orbital overlap [33]. The strong intramolecular hyper conjugation interaction is transferred from π (C3-C4) to π*(C5-N6) bond in the ring, that leads to stabilization of 28.26 kJ/mol as evident from Table.3.Themagnitude of charges transferred from (LP (1) N6) to (C5-C11) shows weak intramolecular interaction. The magnitude of charges transferred from (LP (1) N6) to (C4-C5) and (C1-C2) show that the stabilization energy of about 10.20 kJ/mol and 9.59 kJ/mol respectively. The delocalization of electron π*(C5-N6) to π*(C1-C2) with enormous stabilization energy of about 277.04*kJ/mol

12

4.8. Mulliken Atomic Charges: Mulliken atomic charge calculation has an important role in the application of quantum chemical calculation to molecular system because atomic charges affect dipole moment, molecular polarizability, electronic structure and more a lot of properties of molecular systems.Mulliken’s population analysis provides a partitioning of either a total charge density or an orbital density [34-36]. The calculated Mulliken charge values of 2-Benzylpyridine are listed in Table. S4. The charge distribution of the title molecule shows the Benzene ring hydrogen and carbon atoms are positively charged, whereas the pyridine and methylene group H and C are partially negative and positive. The influence of electronic effect resulting from the hyper conjugation and induction of methylene group in the aromatic ring causes a large negatively charged value in the pyridine carbon and Hydrogen atom of 2-Benzylpyridine. 4.9. Thermodynamic properties The total energy of a molecule is the sum of translational, rotational, vibrational and electronic energies, i.e., E = Et+ Er+ Ev+ Ee. The statistical thermo chemical analysis of DPF is carried out considering the molecule to be at room temperature of 298.15 K and one atmospheric pressure. The thermodynamic parameters, like rotational constant, zero point vibrational energy (ZPVE) of the molecule by DFT method with B3LYP are presented in Table.S5. On the basis of vibrational analysis and statistical thermodynamics, the standard thermodynamic functions: heat capacity (C0p; m), entropy (S0 m), and enthalpy (H0 m) were obtained for temperatures from 100 K to1000 K and the values are tabulated Table.S5. The temperature dependence correlation graphs are shown in Fig.S5, S6, S7. All these thermodynamic data provide helpful information for further study on 2BP. They can be used to compute the other thermodynamic parameters according to relationships of thermodynamic functions and to determine the directions of chemical reactions according to the second law of thermodynamics [37]. 5. Conclusion A complete vibrational analysis of 2 Benzylpyridine were performed by DFT-B3LYP method with 6-31G (d,p) basis set.FTIR and FT-Raman spectra of 2BP were recorded and the detailed vibrational assignments were obtained. The molecular geometry, vibrational frequencies, Infrared intensities and Raman scattering activities of the molecules were calculated using DFT. The calculated HOMO and LUMO energies show that charge transfer occurs within 13

the molecule. 1H and

13

C NMR chemical shifts were compared with experimentalvalues. As a

result, all the vibrational frequencies are calculated and compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are in good agreement.An absorption maximum (λmax) of (2BP) was calculated by CIS method. The title compound exhibit good NLO property and the first order hyperpolarizability value is 2.73 times greater than that of urea. This makes 2BP, a prospective building block for nonlinear optical materials. The stability and intramolecular interactions have been interpreted by NBO/NLO analysis and the transactions give stabilization to the structure have been identified by second order perturbation energy calculations. Mulliken atomic charges and the natural atomic charges obtained are tabulated which gives a proper understanding of the atomic theory. The correlations between the statistical thermodynamics and temperature are also obtained. It was seen that the heat capacities, entropies and enthalpies increase with the increasing temperature owing to the intensities of the molecular vibrations increase with increasing temperature.

6. Acknowledgements The authors are thankful to Sophisticated Analytical InstrumentationFacility (SAIF), IIT Madras,

Chennai,

and

St.

Joseph

College

spectralmeasurements.

14

Trichirapalli,

India

for

providing

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T.Schlick, Molecular Modelling Simulation: An Interdisciplinary Guide, vol,21, second edition, Springer, New York, 2010.

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M. Nakano, H. Fujita, M. Takahata, K. Yamaguchi, J. Am. Chem.Soc, 124(2002) 96489655.

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SpectrochimicaActa Part

Spectroscopy 118 (2014)

663–671.

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R. Sangeetha, D. Barathi, R.

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Molecular

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Biomolecular

Y.X.Sun, Q.L Hao, W.X.Wei, Z.X Yu, L.d.Lu, X.Wang, Y.S.Wang, J.MolStruct. THEOCHEM 904(2009) 74-82

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17

Figure captions Fig.1

Molecular structure of 2 Benzyl pyridine along with numbering of atom.

Fig. 2(a)Theoretical FT IR spectra of 2BP. Fig 2(b) Experimental FT IR spectra of 2BP. Fig. 3(a) Theoretical FT-Raman spectra of 2BP. Fig 3(b) Experimental FT-Raman spectra of 2BP. Fig.4 HOMO PLOT. Fig.5 LUMO PLOT. Fig. S1a Experimental13C NMR Spectrum. Fig. S1b Theoretical 13C NMR Spectrum. Fig. S2a Experimental 1H NMR Spectrum. Fig. S2bTheoretical 1H NMR Spectrum. Fig. S3a Theoretical UV Spectra. Fig. S3b Experimental UV Spectra. Fig. S4 DOS Spectrum. Fig. S5 Correlation graph of Heat capacity Vs Temperature. Fig. S6 Correlation graph of Entropy Vs Temperature. Fig. S7 Correlation graph of Enthalpy Vs Temperature.

18

Table.1. Detailed assignment of fundamental vibrations of 2-Benzylpyridine (2BP) by normal mode analysis based on SQM force field calculations.

SI.NO

Observed

Calculated frequencies(cm-1) with B3LYP/

frequencies(cm-1)

6-31G(d,p) force field

FT IR

FT-Raman

Characterization of normal modes

Unscaled Scaled

IR

Raman

(cm-1)

(cm-1)

Intensity

activity

1

3070

-

3212

3070

16.733

244.507

ν CHP(99)

2

-

-

3206

3064

17.078

281.005

ν CHB(98)

3

-

-

3200

3059

21.381

54.853

ν CHP(98)

4

-

-

3198

3057

21.613

28.042

ν CHB(94)

5

3057

3056

3188

3048

23.889

92.392

ν CHB(100)

6

-

-

3185

3045

5.059

79.887

ν CHP(92)

7

-

-

3178

3038

0.571

93.821

ν CHB(88)

8

3027

-

3169

3029

8.473

38.4

ν CHB(92)

9

-

-

3162

3023

25.613

105.623

ν CHP(95)

10

-

2980

3106

2970

7.951

54.014

ν CH M(94)

11

-

2918

3058

2923

20.874

12

-

1588

1661

1588

13

-

1573

1646

1573

14

-

1569

1641

15

1556

-

16

-

1471

96.868

ν CHM(94) 37.947

ν CCB(52), β CCH(35)

56.444

24.870

ν CCP(54), β CCH(23), ν CN(11)

1569

2.873

6.425

ν CCB(56), β CCH(29)

1628

1556

21.053

9.3402

ν CCP(35), β CCH(30), ν CN(19)

1539

1471

14.913

0.367

ν CCB(58), β CCH(30)

3.386

19

17

1449

-

1516

1449

31.311

0.568

ν CCP(41), β CCH(23), ν CN(13)

18

-

1432

1497

1431

4.799

1.156

β CCHM(43), ν CC(30)

19

-

1424

1490

1424

3.510

18.023

β CCHM(77), ν CC(12)

20

-

1410

1475

1410

29.565

2.421

β CCHP(52), ν CC(20)

21

-

1311

1371

1311

1.27

0.980

ν NCP(42), βCCH(39),ν CC(12)

22

-

-

1362

1302

0.439

1.456

β HCHM(40), ν CC(33)

23

-

1281

1340

1281

1.623

5.324

ν NCP(47), β HCN(35)

24

-

1270

1328

1270

1.813

6.885

β HCNP(38), ν NC(28), ν CC(13)

25

1253

-

1311

1253

0.589

3.464

β CCHP(53), ν NC(22)

26

-

1194

1249

1194

8.738

11.669

ν CCP(38), β CCH(25), ν CN(11)

27

1163

-

1216

1163

2,456

9.036

ν CCB(56), β CCH(29)

28

-

1156

1209

1156

1.144

7.864

ν CCB(55), β CCH(28)

29

1135

-

1187

1135

0.213

10.390

ν CCB(62), β CCH(27)

30

-

-

1185

1132

1.802

6.290

β CCHP(55), ν CC(20)

31

-

1125

1177

1125

2.632

3.200

β CCHP(53), ν CH(28)

32

-

1075

1124

1075

3.748

2.055

β CCHM(62), ν CC(20)

33

1054

-

1102

1054

2.186

0.43

β CCHB(40), ν CC(28)

34

-

1030

1076

1029

4.116

13.332

β CCHB(72), ν CC(10)

35

1011

-

1057

1011

4.420

12.574

ν CCM(46), β CCH(38)

36

972

-

1017

972

0.381

29.554

ν CCM(39), β CCC(30)

37

-

-

1011

966

5.762

17.1

β CCCP(46),ν NC(20), β CCN(11)

38

-

963

1007

963

0.023

0.447

β CCCP(82)

39

956

-

1000

956

0.371

1.586

β CCHB(52), ν CC(21)

40

935

-

978

935

0.1381

1.710

δ CCCHB(50), δ CCCC(23)

20

41

-

933

975

933

0.3795

0.398

δ CCCHB(70), δ CCCC(15)

42

-

904

945

904

1.2984

2.388

δ CCCHB(66), δ CCCC(10)

43

882

-

922

882

2.8804

3.310

δ CCCHB(52), δ NCCC(20)

44

-

867

907

867

0.6098

3.605

δ CCCHP(65), δ NCCC(19)

45

-

-

864

826

0.411

4.926

β CCCB(71), β CCH(10)

46

-

820

858

820

3.125

11.508

δ CCCHB(45), τ CCCC(24)

47

803

-

840

803

2.7071

3.575

β CCCB(42), ν CC(40)

48

-

-

772

738

19.837

7.200

δ CCCHP(54), δ HCCN(20)

49

-

731

765

731

2.198

3.175

δ CCCHP(60), δ CCCN(17)

50

725

-

759

725

24.515

4.575

β CCHB(42), ν CC(25)

51

684

-

716

684

22.886

0.615

β CCHB(53), ν CC(20)

52

-

-

643

615

3.466

6.536

β CCCB(62), β CCN(21)

53

-

608

636

608

1.155

3.655

β CCCB(39), ν CH(29)

54

596

-

623

596

14.577

6.347

β CCCB(42), ν NC(28)

55

-

549

574

549

6.947

3.389

β CCCB(55), ν CC(21)

56

-

-

486

464

2.082

0.196

δ CCCHB(75)

57

-

445

465

445

0.600

2.337

τ CCCCB(40), δ CCCH(33)

58

400

-

418

400

1.851

0.255

τ CCCCB(39), δCCCH(25)

59

-

398

416

398

2.591

0.477

τ CCCCB(42), δCCCH(25)

60

-

357

373

1.329

0.666

δ HCCNP(38), δ CCCN(28)

61

-

265

277

265

0.427

0.972

δ HCNCP(40), δ CCCC(29)

62

-

235

245

234

1.316

6.862

β CCCP(30),ν CN(25), β NCC(18)

63

-

-

179

171

1.483

2.650

τ CNCCM(35), β CCC(27)

357

21

64

-

63

66

63

0.228

8.997

τ CCCCM(54), τ CNCC(25)

65

-

39

40

39

1.095

0.228

τ CCCCM(95)

66

-

-

28

26

1.152

7.536

τ CCCCB(50), τ CCCH(19)

ν- Stretching vibrations, β- bending vibrations, τ- torsional vibrations, δ - out of plane. B-Benzene, M-Methylene, P- Pyridine.

22

Table 2. The predicted polarizability and first hyperpolarizability for the 2BP a.u

e.s.u( 10-

a.u

e.s.u( 10-24)

24)

αxx

155.181

22.9978

βxxx

-120.1327

-1037.8624

αxy

-10.2893

-1.5249

βxxy

-17.8518

154.2271

αyy

130.0742

19.277

βxyy

4.9356

42.6401

αxz

-1.8303

-0.2713

βyyy

-31.8566

-275.2187

αyz

-0.3599

-0.0533

βxxz

-72.9139

-629.9251

αzz

79.2193

11.7403

βxyz

-4.7168

-40.7499

17.9543

βyyz

-3.3467

-28.9131

10.2905

βxzz

-10.5412

-91.0729

αtot 121.1492 ∆α

69.4365

µx

-0.9823

βyzz

-0.4393

-3.7952

µy

-1.232

βzzz

20.3062

175.4314

µz

-1.0759

βtot

117.8057

1017.7585

µ tot 3.2902D

23

Table 3. Second order perturbation theory of Fock matrix for 2BP Donor NBO (i) C1-C2

C1-C2

C1-N6

C1-H8

C2-C3

C2-H9

C3-C4

C3-C4

C3-C7

C4-C5

Type of bond σ

π

σ

σ

σ

σ

σ

π

σ

σ

Occupancy

1.98626

1.64569

1.98509

1.98299

1.98068

1.98216

1.97968

1.65625

1.98356

1.98181

Acceptor NBO(j)

Type of bond

Occupancy

E(2) (Kcal/mol)

Ej–Ei (a.u) F(c),j) (a.u)

C2-C3

σ*

0.01574

2.30

1.28

0.048

C3-C7

σ*

0.01273

2.70

1.18

0.050

C3-C4

π*

0.01490

22.59

0.28

0.072

C5-N6

π*

0.38637

16.10

0.27

0.060

C2-H9

σ*

0.01289

1.58

1.29

0.040

C5-C11

σ*

0.03083

3.50

1.23

0.059

C2-C3

σ*

0.01574

3.65

1.09

0.056

C5-N6

σ*

0.02307

4.75

1.06

0.063

C3-C4

σ*

0.01490

2.46

1.28

0.050

C4-H10

σ*

0.01381

2.51

1.17

0.048

C1-N6

σ*

0.01409

4.38

1.07

0.061

C3-C4

σ*

0.30791

3.28

1.11

0.054

C4-C5

σ*

0.03263

2.69

1.27

0.052

C5-C11

σ*

0.03083

3.35

1.11

0.055

C1-C2

π*

0.30535

17.17

0.28

0.063

C5-N6

π*

0.38637

28.26

0.27

0.079

C1-C2

σ*

0.02569

3.23

1.10

0.053

C4-C5

σ*

0.03262

3.50

1.10

0.056

C3-C4

σ*

0.01490

2.52

1.28

0.051

C3-H7

σ*

0.01273

2.43

1.17

0.048

24

C4-H10

C5-N6

1.98125

C11-H12

C11-H13

C11-C14

C14-C15

C14-C16

C15-C17

σ*

0.01574

3.33

1.10

0.054

C5-N6

σ*

0.02307

4.92

1.06

0.065

σ

1.98351

C1-H8

σ*

0.02075

2.12

1.29

0.047

π

1.70596

C1-C2

π*

0.30535

27.44

0.32

0.083

C3-C4

π*

0.30791

12.98

0.32

0.057

C1-N6

σ*

0.01409

3.37

1.16

0.056

C14-C16

π*

0.02181

1.84

0.66

0.034

C5-N6

π*

0.38637

1.13

0.50

0.053

C14-C16

π*

0.02181

2.75

0.54

0.037

C5-N6

σ*

0.02307

3.42

1.03

0.053

C5-N6

π*

0.38637

1.05

0.51

0.023

C5-N6

π*

0.38637

2.77

0.62

0.041

C15-C17

σ*

0.01484

2.25

1.20

0.047

C14-C16

σ*

0.02305

3.37

1.27

0.058

C15-C17

σ*

0.31672

2.65

1.27

0.052

C14-C15

σ*

0.02305

3.37

1.27

0.058

C15-H18

σ*

0.01398

2.10

1.18

0.045

π C5-H11

C2-C3

σ

σ

σ

σ

σ

σ

1.97181

1.97080

1.97973

1.96769

1.97484

1.97612

σ

1.97935

C11-C14

σ*

0.02420

3.38

1.10

0.054

π

1.67021

C14-C16

π*

0.02181

20.88

0.28

0.069

π

1.67021

C19-C21

π*

0.01570

20.17

0.28

0.067

C15-H18

σ

1.98104

C14-C16

σ*

0.02181

4.08

1.09

0.060

C16-C19

σ

1.97919

C11-C14

σ*

0.02420

3.47

1.10

0.055

C14-C16

σ*

0.02305

3.08

1.27

0.056

C14-C15

σ*

0.02305

3.99

1.16

0.059

C16-H20

σ

1.98238

25

C17-C21

σ

C17-H22 C19-C21

C19-H23

σ

σ

1.98092

C15-C17

σ*

0.31672

2.56

1.28

0.051

C15-H18

σ*

0.01398

2.30

1.18

0.047

1.98291

C14-C15

σ*

0.02305

2.56

1.28

0.051

1.98063

C16-C19

σ*

0.01498

2.59

1.27

0.051

C16-H20

σ*

0.01349

2.37

1.16

0.047

C14-C16

σ*

0.02181

3.75

1.10

0.057

1.98279

1.11

C21-H24

σ

1.98308

C15-C17

σ*

0.01484

3.50

N6

LP(1)

1.92228

C1-C2

σ*

0.02569

9.59

0.90

0.084

N6

LP(1)

C1-H8

σ*

0.02075

2.90

0.81

0.044

C5-N6

π*

C1-C2

π*

0.30535

229.87

0.01

0.079

0.30791

277.04

0.01

0.085

0.38637

C3-C4

π*

26

0.056

Fig.1.Molecular structure of 2 Benzyl pyridine along with numbering of atom.

27

Fig. 2(a) Theoretical FT IR spectra of 2BP.

Fig.2(b) Experimental FT IR spectra of 2BP. 28

Fig. 3(a) Theoretical FT-Raman spectra of 2BP

Fig.3(b) Experimental FT-Raman spectra of 2BP.

29

.

Fig.4 HOMO PLOT.

30

Fig.5 LUMO PLOT.

31

GRAPHICAL ABSTRACT

32

HIGHLIGHTS

•

Pyridines are involved in bioactivities with applications in pharmaceutical drugs and agricultural products.

•

The dipole moment and first hyperpolarizability of the title molecule is approximately 2.396, 2.73 times than those of urea.

•

HOMO– LUMO of title molecule, reveals that the energy gap reflect the chemical activity

•

Estimated chemical shifts, correlation coefficients are in agreement with the observed result

33