Vibrational spectra, molecular structure, NBO, NMR, UV, first order hyperpolarizability, analysis of (S)-(−)-N-(5-Nitro-2-pyridyl) alaninol by Density functional theory

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Vibrational spectra, molecular structure, NBO, NMR, UV, first order hyperpolarizability, analysis of (S)-()-N-(5-Nitro-2-pyridyl) alaninol by Density functional theory K. Govindarasu, E. Kavitha ⇑ Department of Physics (Engg.), Annamalai University, Annamalainagar 608 002, India

h i g h l i g h t s

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

 The FTIR and FT-Raman spectra of

Optimized molecular structure of (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

SN5N2PLA were reported.  The first order hyperpolarizability was calculated.  UV–Vis spectra were recorded and compared with calculated values. 1 13  H and C NMR spectra were recorded and analyzed.

a r t i c l e

i n f o

Article history: Received 6 November 2013 Received in revised form 30 January 2014 Accepted 16 February 2014 Available online 4 March 2014 Keywords: NBO UV–Vis NMR Hyperpolarizability (S)-()-N-(5-Nitro-2-pyridyl) alaninol

a b s t r a c t In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic resonance studies of (S)-()-N-(5-Nitro-2-pyridyl) alaninol (abbreviated as SN5N2PLA) were investigated by utilizing HF and DFT/B3LYP with 6-31G(d, p) as basis set. The Fourier transform infrared (FT-IR) and FT-Raman spectra of SN5N2PLA were recorded in the region 4000–400 cm1 and 3500–50 cm1, respectively. Complete vibrational assignments, analysis and correlation of the fundamental modes for the title compound were carried out. UV–Visible spectrum of the compound that dissolved in methanol were recorded in the region 200–800 nm and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The molecular stability and bond strength have been investigated by applying the Natural Bond Orbital (NBO) analysis. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of SN5N2PLA were calculated using the GIAO method in methanol solution and compared with the measured experimental data. The dipole moment, polarizability and first order hyperpolarizability values were also computed. The polarizability and first hyperpolarizability of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The Chemical reactivity and Thermodynamic properties of SN5N2PLA at different temperature are calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs) analysis were investigated using theoretical calculations. Published by Elsevier B.V.

⇑ Corresponding author. Tel.: +91 9442477462. E-mail address: [email protected] (E. Kavitha). http://dx.doi.org/10.1016/j.saa.2014.02.107 1386-1425/Published by Elsevier B.V.

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

Introduction The organic molecules exhibiting nonlinear optical (NLO) properties have been motivated by their potential for applications in optical communications, optical computing, data storage, dynamic holography, harmonic generators, frequency mixing, and optical switching [1,2]. The advantages of using organic molecules as NLO materials are that they can be designed to optimize the desired NLO property by having different donor and acceptor groups in the molecules. At the molecular level, compounds are expected to exhibit large values of molecular hyperpolarizability (b) if they possess polarizable electrons, for example, p-electrons spread over a larger distance. It has been reported that extended p conjugated systems with terminal donor–acceptor substituents to exhibit large b values [3,4]. The nitropyridine derivatives are particularly interesting because they form an acceptor fragment of 2-adamantylamino-5-nitropyridine (AANP), which showed a very large nonlinearity among the materials reported earlier [5]. Marchewka et al. [6] reported Crystal and molecular structure of N-(4nitrophenyl)-b-alanine-its vibrational spectra and theoretical calculations. Kanetake et al. [7] reported Extractive spectrophotometric determination of palladium with Di-2-pyridylmethanone 2-(5-Nitro) pyridylhydrazone. Kohatha et al. [8] reported synthesis and chromogenic properties of some water-soluble 5-Nitro-2-pyridilhydrozones. Chan-il Park et al. [9] reported spectrophotometric determination of copper after selective extraction with a-(2Benzimidazolyl) a0 -a00 -(N-5-nitro-2-pyridyl hydrazone)-toluene. To the best of our knowledge, neither quantum chemical calculation, nor the vibrational spectra of SN5N2PLA have been reported. The present work mainly deals with experimental FT-IR and FT-Raman spectra, vibrational assignments using total energy distribution (TED) and NLO activity as well as HF and DFT/B3LYP calculations for SN5N2PLA. In addition, the first order hyperpolarizability, NMR analysis and UV spectral analysis of SN5N2PLA have been investigated. The theoretically predicted values have been compared with the experimentally measured data and also the results have been discussed. Nowadays NIR–FT-Raman spectroscopy combined with quantum chemical computations has been recently used as an effective tool in the vibrational analysis of drug molecules [10], biological compounds [11] and natural products [12]. Since fluorescence-free Raman spectra and the computed results can help unambiguous identification of vibrational modes as well as the bonding and structural features of complex organic molecular systems. HOMO–LUMO analysis have been performed by applying density functional theory calculations based on B3LYP with 6-31G(d, p) as basis set. We have also performed NBO calculation to provide a convenient basis for investigating charge transfer or conjugative interaction in molecular systems.

ultraviolet absorption spectra of SN5N2PLA were examined in the range 200–800 nm using Cary 5EUV–VIS–NIR spectrometer. The UV pattern is taken from a 10–5 M solution of SN5N2PLA, dissolved in methanol. NMR spectra are recorded on Bruker AVANCE III 500 MHz (AV 500) spectrometer; chemical shifts are expressed in ppm (d units) relative to TMS signal as internal reference in methanol. The theoretically predicted IR and Raman spectra at B3LYP/6-31G(d, p) level calculation along with experimental FTIR and FT-Raman spectra are shown in Figs. 1 and 2. The spectral measurements were carried out at Indian Institute of Technology (IIT), Chennai.

Computational details The density functional theory DFT/B3LYP with the 6-31G(d, p) as basis set was adopted to calculate the properties of SN5N2PLA in the present work. All the calculations were performed using Gaussian 03W program package [13] with the default convergence criteria without any constraint on the geometry [14]. The assignments of the calculated wavenumbers are aided by the animation option of Gauss View 3.0 graphical interface for Gaussian programs, which gives a visual presentation of the shape of the vibrational modes along with available related molecules [15]. Furthermore, theoretical vibrational spectra of the title compound were interpreted by means of TED using the VEDA 4 program [16]. The optimized structural parameters were used in the vibrational frequency calculations at DFT levels to characterize all stationary points as minima. As the hybrid B3LYP functional tends to overestimate the fundamental normal modes of vibration, the computed frequencies were scaled with appropriate values to bring harmonization between the theoretical and experimental wavenumbers [17]. Vibrational frequencies were computed at DFT level which had reliable one-to-one correspondence with experimental IR and Raman frequencies [18]. 1H and 13C NMR chemical shifts were calculated with GIAO approach [19,20] by applying B3LYP method [21,22]. The Natural Bond Orbital (NBO) calculations were performed using NBO 3.1 program [23] as implemented in the Gaussian 03W [13] package at the DFT/B3LYP level; in order to understand various second order interactions between filled orbital of one subsystem and vacant orbital of another subsystem, which is a measure of the intermolecular delocalization or hyper conjugation.

Prediction of Raman intensities The Raman activities (SRa) calculated with Gaussian 03 program [13] converted to relative Raman intensities (IRa) using the following relationship derived from the intensity theory of Raman scattering [24,25]

Experimental details The compound (S)-()-N-(5-Nitro-2-pyridyl) alaninol in the solid form was purchased from TCI INDIA chemical company at Chennai, with a stated purity greater than 98% and it was used as such without further purification. The FT-IR spectrum of this compound was recorded in the range of 4000–400 cm1 on a Perkin Elmer FT-IR spectrometer using KBr pellet technique. The spectrum was recorded in the room temperature, with scanning speed of 10 cm1. FT-Raman spectrum of the title compound was recorded using 1064 nm line of Nd:YAG laser as excitation wavelength in the region 3500–50 cm1 on a BRUKER RFS 27: FT-Raman Spectrometer equipped with FT-Raman molecule accessory. The spectral resolution was set to 2 cm1 in back scattering mode. The laser output was kept at 100 mW for the solid sample. The

499

Ii ¼

f ðv o  v i Þ4 Si v i ½1  expðhcv i =ktÞ

Where m0 is the laser exciting wavenumber in cm1 (in this work, we have used the excitation wavenumber m0 = 9398.5 cm1, which corresponds to the wavelength of 1064 nm of a Nd-YAG laser), mi the vibrational wavenumber of the ith normal mode (cm1) while Si is the Raman scattering activity of the normal mode mi. f (is a constant equal to 1012) is a suitably chosen common normalization factor for all peak intensities. h, k, c and T are Planck and Boltzmann constants, speed of light and temperature in Kelvin, respectively. For the simulation of calculated FT-Raman spectra have been plotted using pure Lorentizian band shape with a bandwidth of Full Width at Half Maximum (FWHM) of 10 cm1.

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

IR intencity (arb.units)

500

4000

3500

3000

2500

2000

1000

500

1500

1000

500

Transmittance (%)

Wavenumber

1500

(cm-1)

4000

3500

3000

2500

2000

Wavenumber

(cm-1)

Fig. 1. Comparison of theoretical B3LYP/6-31G(d, p) 1(a) and experimental 1(b) FT-IR spectra for (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

Results and discussion Conformational stability In order to describe conformational flexibility of the title molecule, the energy profile as a function of (N2–C3–C4–H21) and (N2– C3–C1–O5) torsion angles were achieved with B3LYP/6-31G(d, p) method. Potential energy surface (PES) scan in N2–C3–C4–H21 and N2–C3–C1–O5 dihedral angles was performed. The scan was carried out by minimizing the potential energy in all geometrical parameters by changing the torsion angle every 10° for 180° rotation around the bond. The shape of the potential energy as a function of the dihedral angles are illustrated in supplementary material S1. The conformational energy profile shows two maxima near 180° and 300° for N2–C3–C4–H21 torsion angle. The maximum energies are obtained 638.9988 and 567.2617 Hartree for 180° and 300° respectively. It is clear from supplementary material S1, there are two local minima (stable conformers) observed at 0° or 360° having the energy of 701.2153 Hartree and 240° having the energy of 701.1502 Hartree for T (N2–C3–C4– H21). Similarly one maximum energy is obtained at 170° having the energy 700.144 Hartree and one local minima (stable

conformers) observed at 0° or 360° having the energy 701.279 Hartree for dihedral angle T (N2–C3–C1–O5). Therefore, the most stable conformer is for 0° torsion angle for (N2–C3–C4– H21) and (N2–C3–C1–O5) rotation. Further results are based on the most stable conformer of SN5N2PLA molecule to clarify molecular structure and assignments of vibrational spectra. Molecular geometry The optimized geometric parameters such as bond lengths, bond angles and dihedral angles of the title molecule were given in Table 1 using HF and density functional theoretical calculation with 6-31G(d, p) basis set. The atom numbering scheme adopted in this study is given in Fig. 3. Owing to the absence of experimental data the title molecule is compared with XRD data of closely related molecule 2-Amino-5-nitropyridinium tetraoxidorhenate(VII) monohydrate [26]. From the theoretical values we found that most of the optimized bond lengths and bond angles are slightly smaller, as well as longer than the experimental values in both HF and DFT levels. This is due to fact that the theoretical calculations belong to isolated molecule in gaseous phase and experimental results belong to molecule in solid state. The optimized bond length of

501

Raman intensity (arb.units)

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

3500

3000

2500

2000

1500

1000

500

1000

500

Raman intensity (arb.units)

Wavenumber (cm-1)

3500

3000

2500

2000

1500

Wavenumber (cm-1) Fig. 2. Comparison of theoretical B3LYP/6-31G(d, p) 2(a) and experimental 2(b) FT-IR spectra for (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

C–C in the molecule fall in the range 1.381–1.538 Å at B3LYP and 1.368–1.527 Å at HF methods shows good agreement with recorded X-ray data of 1.360–1.413 Å. The optimized bond lengths of C–N in the molecule fall in the range 1.328–1.467 Å at B3LYP and 1.313–1.459 Å at HF methods are very close to recorded X-ray data of 1.341–1.446 Å. The optimized bond lengths of C–H in the molecule fall in the range 1.083–1.102 Å at B3LYP and 1.071–1.089 Å at HF methods are clearly coincide with observed X-ray data of 0.930 Å. The average N–O distance of 1.234 Å in the nitro group is an indication of clearly double bonds. The bond angle O13–N12–O14 (124.5°) of nitro group at both B3LYP and HF methods which is closer to experimental data (123.3 Å). The bond angle between nitrogen of the pyridine ring and nitrogen of the NH group N2–C6–N11 (114.4°) at B3LYP method and (114.8°) at HF method which is smaller than the experimental finding (119.2°). The dihedral angles are calculated according to the atoms N2– C6–C7–C8 (179.42°) at B3LYP method and (179.99°) at HF method and C7–C8–C9–N12 (179.97°) at B3LYP method and (179.95°) at HF method which is good agreement with experimental data at (179.9°) and (179.5°).

Vibrational assignments Density functional theory is known for good performance in the estimation of vibrational spectra of organic compounds, and it can be observed in the molecule SN5N2PLA.The combined FTIR and FT– Raman spectra of the title compound under investigation are shown in Figs. 1 and 2. The observed and calculated frequencies using HF/6-31G(d, p) and B3LYP/6-31G(d, p) basis set and along with their relative intensities, probable assignments and the total energy distribution (TED) of the title molecule are summarized in Table 2. A complete assignment of the fundamentals was proposed based on the calculated TED values, infrared and Raman intensities. According to the theoretical calculations, SN5N2PLA has structure of C1 point group symmetry. The molecule has 25 atoms and 69 normal modes of vibrations. Theoretically all the fundamental vibrations are active in both IR and Raman. The results showed that the HF and DFT (B3LYP) methods applied in this work leads to vibrational wavenumbers which are in good agreements with the experimental data. The small difference between the experimental and calculated vibrational modes could be attributed to the fact

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K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

Table 1 Calculated optimized parameter values of the (S)-()-N-(5-Nitro-2-pyridyl) alaninol [Bond length in (Å), angles in (°)].

a

Bond length

B3LYP

HF

Expa

Bond angle

B3LYP

HF

Expa

Dihedral angle

B3LYP

HF

Expa

C1–C3 C1–O5 C1–H15 C1–H16 N2–C3 N2–C6 N2–H17 C3–C4 C3–H18 C4–H19 C4–H20 C4–H21 O5–H22 C6–C7 C6–N11 C7–C8 C7–H23 C8–C9 C8–H24 C9–C10 C9–N12 C10–N11 C10–H25 N12–O13 N12–O14

1.538 1.417 1.102 1.095 1.467 1.369 1.013 1.531 1.096 1.093 1.094 1.096 0.967 1.418 1.353 1.381 1.083 1.399 1.083 1.396 1.451 1.328 1.085 1.234 1.234

1.527 1.397 1.089 1.084 1.459 1.358 0.996 1.527 1.084 1.084 1.085 1.087 0.944 1.410 1.332 1.368 1.071 1.391 1.072 1.382 1.438 1.313 1.073 1.196 1.196

– – – – – 1.313 0.890 – – – – – – 1.413 1.358 1.351 0.930 1.402 0.930 1.360 1.446 1.341 0.930 1.216 1.217

C3–C1–O5 C3–C1–H15 C3–C1–H16 O5–C1–H15 O5–C1–H16 H15–C1–H16 C3–N2–C6 C3–N2–H17 C6–N2–H17 C1–C3–N2 C1–C3–C4 C1–C3–H18 N2–C3–C4 N2–C3–H18 C4–C3–H18 C3–C4–H19 C3–C4–H20 C3–C4–H21 H19–C4–H20 H19–C4–H21 H20–C4–H21 C1–O5–H22 N2–C6–C7 N2–C6–N11 C7–C6–N11 C6–C7–C8 C6–C7–H23 C8–C7–H23 C7–C8–C9 C7–C8–H24 C9–C8–H24 C8–C9–C10 C8–C9–N12 C10–C9–N12 C9–C10–N11 C9–C10–H25 N11–C10–H25 C6–N11–C10 C9–N12–O13 C9–N12–O14 O13–N12–O14

112.6 109.3 109.3 111.5 106.4 107.7 126.4 117.0 112.1 110.9 111.4 107.8 109.8 107.8 109.0 111.0 110.6 111.0 108.2 108.3 107.6 107.1 123.0 114.4 122.5 118.3 120.6 121.0 118.7 121.8 119.5 119.4 120.4 120.2 122.7 119.8 117.5 118.4 117.7 117.8 124.5

112.2 109.5 109.5 111.1 106.7 107.7 126.6 116.8 112.2 110.9 111.3 108.0 109.7 108.2 108.6 110.8 110.6 111.1 108.2 108.3 107.8 109.2 123.0 114.8 122.2 118.2 121.0 120.8 118.8 121.2 120.0 119.1 120.5 120.3 122.5 120.3 117.2 119.1 117.7 117.9 124.5

– – – – – – – – – – – – – – – – – – – – – – 122.8 119.2 118.0 120.0 120.0 120.0 118.9 120.6 120.6 121.3 120.1 118.6 118.5 120.7 120.7 123.2 117.7 119.0 123.3

O5–C1–C3–N2 O5–C1–C3–C4 O5–C1–C3–H18 H15–C1–C3–N2 H15–C1–C3–C4 H15–C1–C3–H18 C16–C1–C3–N2 C16–C1–C3–C4 C16–C1–C3–H18 C3–C1–O5–H22 H15–C1–O5–H22 H16–C1–O5–H22 C6–N2–C3–C1 C6–N2–C3–C4 C6–N2–C3–H18 H17–N2–C3–C1 H17–N2–C3–C4 H17–N2–C3–H18 C3–N2–C6–C7 C3–N2–C6–N11 H17–N2–C6–C7 H17–N2–C6–N11 C1–C3–C4–H19 C1–C3–C4–H20 C1–C3–C4–H21 N2–C3–C4–H19 N2–C3–C4–H20 N2–C3–C4–H21 H18–C3–C4–H19 H18–C3–C4–H20 H18–C3–C4–H21 N2–C6–C7–C8 N2–C6–C7–H23 N11–C6–C7–C8 N11–C6–C7–H23 N2–C6–N11–C10 C7–C6–N11–C10 C6–C7–C8–C9 C6–C7–C8–H24 H23–C7–C8–C9 H23–C7–C8–H24 C7–C8–C9–C10 C7–C8–C9–N12 H24–C8–C9–C10 H24–C8–C9–N12 C8–C9–C10–N11 C8–C9–C10–H25 N12–C9–C10–N11 N12–C9–C10–H25 C8–C9–N12–O13 C8–C9–N12–O14 C10–C9–N12–O13 C10–C9–N12–O14 C9–C10–N11–C6 H25–C10–N11–C6

57.50 179.86 60.26 66.94 55.71 175.30 175.49 61.87 57.73 67.92 55.28 172.38 101.60 134.82 16.20 104.21 19.38 138.00 21.95 159.38 177.22 4.11 176.64 56.52 62.84 60.11 179.77 60.41 57.74 62.38 178.26 179.42 3.60 2.02 174.96 180.00 1.32 0.90 179.99 176.07 3.04 0.77 179.97 178.36 0.84 1.54 178.84 179.26 0.36 0.47 179.56 179.66 0.37 0.48 179.89

58.40 179.18 60.03 65.45 56.97 176.13 176.67 60.91 58.24 71.61 51.35 168.49 104.93 131.72 13.33 100.66 22.68 141.07 21.74 159.68 177.12 4.30 177.07 57.02 62.59 59.86 179.90 60.48 58.29 61.75 178.63 179.99 2.54 1.52 175.93 179.61 1.02 0.64 179.90 176.81 2.44 0.63 179.95 178.64 0.69 1.19 179.19 179.49 0.14 0.61 179.43 179.92 0.12 0.35 180.01

– –  – – – – – – – – – – – – – – – – – – – – – – – – – – – – 179.9 – 0.1 – 179.9 0.1 0.2 – – – 0.4 179.5 – – 0.4 – 179.5 – 1.0 177.2 179.9 1.9 0.1 –

Taken from Ref. [26].

that the experimental results belong to solid phase while the theoretical belong to isolated gaseous phase. The calculated vibrational frequencies were scaled in order to improve the agreement with the experiment values. In our study we have followed scaling factor of 0.9026 for HF/6-31G(d, p) and 0.9608 for B3LYP/631G(d, p) respectively. After scaling with a scaling factor [27], the deviation from the experiments is less than 10 cm1 with few exceptions. Comparison of the frequencies calculated at (B3LYP) method using 6-31G(d, p) basis set with experimental values reveals that the 6-31G(d, p) basis set result shows very good agreement with experimental observations, even for a complex molecular system.

O–H vibrations The O–H stretching vibrations normally appear around 3600 cm1 as in phenol [28]. Bands due to O–H stretching are of medium to strong intensity in the infrared spectrum, although it may be broad. In Raman spectra the band is generally weak. Unassociated hydroxyl groups absorbs strongly in the region 3670– 3580 cm1. For solids, liquids and concentrated solutions a broad band of less intensity is normally observed [29]. In our case O–H stretching vibration observed at 3656 cm1 at B3LYP method and 3773 cm1 HF method, and no O–H stretching bands observed in the experimental methods as shown in Table 2. The TED corresponding to this vibration is a pure stretching mode and it is

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

503

Fig. 3. Optimized molecular structure and atomic numbering of (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

exactly contributing to 100%. Some researchers [30,31] have assigned C–OH stretching mode around 1200 cm1 in substituted benzenes and pyridines. The C–OH in-plane bending mode observed at 1184 cm1 in experimental FT Raman spectrum and 1036 cm1 in FTIR spectrum. C–OH in-plane bending vibration also calculated in 1178 cm1 at B3LYP method and 1180 cm1 at HF method shows good agreement with experimental observations. The O–H in-plane bending vibration for phenyl, in general lies in the region 1150–1250 cm1 and it is not much affected due to hydrogen bonding unlike that of stretching and out-of-plane bending wavenumber [32]. For our molecule, the O–H Out of plane bending vibration appears in theoretically computed wavenumbers at 894 cm1 in B3LYP and 903 cm1 in HF methods. The TED corresponding to this vibration suggests that it is a weak mode and exactly contributing to 29%. This band is experimentally observed at 883 cm1 in FTIR spectrum. N–H vibrations The N–H stretching modes of secondary amides are generally observed in the region of 3460–3300 cm1 for N–H stretching and a weak band at 3100–3070 cm1 for an overtone of the N–H band [33]. For the title compound, the very strong band observed at 3252 cm1 in the IR spectrum is assigned as N–H stretching mode. The calculated wavenumber for this mode is at 3456 cm1 in B3LYP method and 3480 cm1 in HF method. This mode is a pure stretching mode, and as it is evident from the TED column they are almost contributing 100%. The wavenumber (3456 cm1) computed by B3LYP/6-31G(d, p) method shows the deviation (204 cm1) when compared with experimental IR data (3252 cm1). This may be due to intermolecular hydrogen bonds in solid state between the NH group and the pyridine N atom. This is the reason for the downshift of NH band at 3252 cm1. The weak N–H in-plane bending mode observed at 1405 cm1 in FTIR spectrum and 1329 and 1504 cm1 in FT-Raman spectrum. The calculated wavenumber for this mode is at 1419 cm1 at B3LYP method and 1465 cm1 at HF method. The out of plane bending vibration observed at 922 cm1 in FTIR spectrum. The calculated wave number for this mode is at 942 and 944 cm1 in B3LYP method and 954 and 1002 cm1 in HF method. Theoretically predicted values are coinciding very well with the observed frequencies. The TED corresponding to this vibration suggests that it (mode. No. 40) is a medium mode and exactly contributing to 73%. C–H vibrations The hetero aromatic structure shows the presence of C–H stretching vibrations in the range of 3100–3000 cm1 [34] which is the characteristic region for the ready identification of C–H stretching vibrations, and the bands are not affected by the nature of substitutions. In the present study the C–H stretching band

observed at 2939 and 3073 cm1 in FT-Raman spectrum. The computed wavenumbers for these modes are at 2919, 3073, 3076 and 3090 cm1 in HF method and 2941, 3089, 3105 and 3117 cm1 in B3LYP method assigned C–H stretching vibrations. The C–H in-plane bending vibrations normally occur as a number of strong-to-weak intensity sharp bands in the region 1300– 1000 cm1 [35,36]. In our molecule the C–H in plane bending vibrations are observed at 1101 and 1294 cm1 in FTIR spectrum 1184, 1295, 1329, and 1351 cm1 in FT-Raman spectrum. The calculated wavenumbers at 1419, 1281, 1101, 1178, 1325 and 1348 cm1 in B3LYP method and 1119, 1180, 1319, 1304 and 1401 cm1 in HF level assigned to C–H in plane bending vibrations. Swaminathan et al. assigned C–H out of plane bending modes in the region 1405 cm1 [37]. In our case the C–H out of plane vibrations are observed in 1405 cm1 in FTIR spectrum. The calculated wave numbers for this mode at 1377 and 1419 cm1 in B3LYP level and 1417 and 1465 cm1 HF level assigned to C–H out of plane bending vibrations. The TED corresponding to this vibration suggests that it (mode. No. 19) is a medium mode and exactly contributing to 41%. C–C vibrations Carbon–carbon ring stretching vibrations occur in the region 1430–1625 cm1. In general, the bands are of variable intensity and are observed at 1625–1590, 1575–1590, 1470–1540, 1430– 1465 and 1280–1380 cm1 from the wavenumber ranges given by Varsanyi [36] for the five bands in the region. The (C–C) stretching modes are normally observed in the range 1650–1400 cm1 in benzene derivatives [38]. In the present molecule the peaks observed at 1405 cm1 in FT-IR spectrum and 858, 1148, 1504, 1583 cm1 in FT-Raman spectrum are assigned to C–C stretching vibrations. The calculated wavenumber for this vibrational mode is at 854, 1146, 1502 and 1582 cm1 at B3LYP method and 872, 1167, 1538 and 1623 cm1 at HF method are assigned to C–C stretching vibrations. The C–C–C bending bands always occur below 600 cm1 [38]. In the present work, the computed values at 198, 285, 621, 664, 793, 986 cm1 in B3LYP level and at 199, 292, 628, 675, 809 and 1022 cm1 in HF method are assigned C–C–C in-plane bending vibrations. The bands observed at 622 and 697 cm1 in FT-IR spectrum and 637 cm1 in FT-Raman spectrum in our molecule is assigned to C–C–C in-plane bending vibration. C–N vibrations The identification of C–N stretching vibrations is a very difficult task, since the mixing of several bands is possible in this region. However, with the help of the animation option of Gauss View 3.0 graphical interface for Gaussian programs and TED value from VEDA 4 program, the C–N stretching vibrations are identified and assigned in this study. The C–N stretching vibrations are always

Mode nos.

Experimental wavenumbers/cm1

Theoretical wavenumbers/cm1

Vibrational assignments with TED (P10%)

HF/6-31G(d, p) FT-IR 3252

3073

2939 2801 1583

1481 1458

1504 1460

1405

1351 1330 1294

1329 1295

1184 1148 1101

1103

1036 951 922 883 858

761

697 622

637

529 505

532 508

B3LYP/6-31G(d, p)

Unscaled

Scaled

IIRa

IRab

Unscaled

Scaled

IIRa

IRab

4180 3855 3423 3408 3404 3273 3263 3248 3234 3185 3166 1851 1798 1761 1704 1642 1634 1627 1623 1607 1570 1564 1552 1519 1500 1461 1444 1425 1341 1308 1293 1285 1240 1235 1199 1167 1132 1115 1110 1060 1000 966 960 935 896 872 834 748 696 630 590 562

3773 3480 3090 3076 3073 2954 2945 2931 2919 2875 2858 1670 1623 1590 1538 1482 1474 1469 1465 1450 1417 1411 1401 1371 1354 1319 1304 1286 1210 1180 1167 1160 1119 1114 1082 1053 1022 1006 1002 956 903 872 867 844 809 787 753 675 628 568 533 508

46.88 59.80 1.82 0.10 0.76 34.82 76.86 8.88 7.00 37.59 49.80 571.88 447.30 42.80 229.43 24.36 207.26 143.03 60.10 343.05 262.44 163.93 15.29 24.05 10.79 218.08 3.81 8.81 36.15 18.11 98.40 18.65 135.76 9.73 84.48 2.46 0.45 2.72 16.10 0.59 4.06 29.78 0.85 24.98 17.25 70.65 2.47 23.80 3.15 96.33 25.55 1.92

7.96 15.25 19.08 10.41 14.59 21.31 29.1 4.19 15.66 36.49 15.49 0.73 83.69 1.49 3.15 5.55 100 53.7 27.72 30.22 15.31 15.37 2.29 8.68 2.81 17.27 4.06 0.58 6.28 3.51 2 53.95 24.07 2.22 4.02 4.04 0.59 2.62 2.23 2.89 3.82 13.61 6.47 2.23 8.09 4.35 0.8 2.13 5.29 8.02 2.28 4.83

3805 3597 3244 3231 3215 3137 3119 3095 3061 3046 2994 1656 1646 1597 1563 1515 1513 1507 1477 1456 1433 1419 1403 1390 1385 1379 1333 1325 1280 1226 1192 1186 1146 1136 1085 1082 1026 1003 982 981 931 889 872 846 826 774 736 691 647 589 546 526

3656 3456 3117 3105 3089 3014 2997 2973 2941 2927 2876 1591 1582 1534 1502 1456 1454 1448 1419 1399 1377 1364 1348 1336 1331 1325 1281 1274 1230 1178 1146 1140 1101 1092 1042 1040 986 964 944 942 894 854 838 813 793 744 707 664 621 565 524 505

18.57 48.66 1.47 0.19 0.60 19.24 29.77 29.76 11.18 17.51 58.90 374.26 285.42 30.96 273.71 4.02 8.15 1.00 5.45 74.72 21.47 11.21 34.92 645.33 105.20 0.51 124.33 13.96 15.68 31.42 59.48 38.06 83.04 21.72 21.99 55.63 11.29 2.53 0.54 3.01 2.64 8.22 8.16 15.95 20.35 25.13 4.08 14.04 5.53 92.37 16.70 1.94

28.54 58.88 34.76 19.57 3.99 5.5 6.91 7.12 1.63 9.97 7.21 5.16 4.11 0.42 2.8 2.37 2.9 0.14 7.66 0.54 0.28 0.48 9.48 100 11.48 4.58 6.18 3.03 4.07 1.49 2.35 3.74 10.11 2.07 2.17 1.26 0.39 0.42 2.04 1.53 2.27 1.97 13.42 2.38 0.14 0.91 0.94 1.29 2.5 7.48 2.04 3.01

tO5H22(100) tN2H17(100) tCH(95) py.ring breathing tCH(95) ass.str in py.ring tCH(99) sym.str py.ring tCH(99) ass.str in CH3 tCH(92) ass.str in CH3 tCH(88) ass.str in CH2 tCH(90) sym str. C3H18 tCH(94) breathing in CH3 tCH(92) sym str.in CH2 tCC(55) py.ring + tassON(15) tCC(71) py.ring + tassON(12) tCC(63) py.ring + tassON(47) tCC(12) py.ring + dHCC(14) py.ring dHCH(71) in CH3 + dH19C4C3C1 (14) dHCH(71) in CH2 + dH19C4C3C1 (18) dHCH(72) sci in CH2 tCC(15) in py ring + dH17N2C6 (27)+dHCC(11) in pyr.ring + cC3H18C4H19(41) tCC(49) in py ring + dHCC(12) in pyr.ring dHCH(70) CH2 rocking + cC3H18C4H19 (13) dHCH(18) CH2 rocking tN12O13(10) + dH18C3C1 (24) + dH18C3N2(31) t N12O14(60) + dH18C3N2(11) dH15C1C3(13) + dH18C3N2(19) tNC(53) pyr.ring + dH24C8C9(14) dH18C4C3(32) dH25C10C9(55) tCC(31) pyr.ring d H22O5C1(20) + dH23C7C6(32) tC1C3(18) + dH16C1C3C4(19) tN12C9(15) + dH25C10C9(32) dH24C8C9(16) + dC3C1O5(25) + dC3C1N2(18) dH24C8C9(25) tC3C4(77) tC1C3(45) dCCC(71) pyr.ring s H25C10N11C6(74) tCC(23) in.pyr.ing + dH18C1C3C4(19) + cCCNH(73) sHCNC(78) + cCCNH(73) cC3C1O5H22(29) + dH18C1C3C4(23) tC1C3(39) + dHCCC(16) pyr.ring tCC(19) pyr.ring + dN12O13O14(18) sH23C7C6N2(70) dN12O13O14(13) + dC3N2C6(22) + dC8C9C10(18) pyr. ring dC10N11C6C7(75) pyr. ring dC6N11C10C9(80) pyr .ring dN12O13O14(34) + dC8C9C10(11) pyr. ring dC7C8C9(59) pyr.ring sH19N2C6N11(58) dC9N12O13(62) dC1C3N2(44)

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

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

FT-Raman

504

Table 2 Comparison of the experimental and calculated vibrational spectra and proposed assignments of (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

505

mixed with other bands and normally occur in the region 1266– 1382 cm1 [39–41]. In our study the C–N stretching vibration observed at 1329 cm1 in FT-Raman spectrum. This vibration theoretically calculated at 1325, 1140 and 439 cm1 in B3LYP method and 1319, 1160 and 443 cm1 in HF method shows good agreement with experimental findings.

IIR-IR Intensity (Kmmol1). IRa-Raman intensity (Arb units) (intensity normalized to 100%). a

b

m-stretching; d-in-plane-bending; c-out-of-plane bending; s-torsion; w-weak; s-strong; vs-very strong; vw-very weak; m-medium.

134

53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69

475

249

548 503 491 469 415 399 323 302 285 254 221 148 141 103 83 52 41

495 454 443 423 375 360 292 272 257 230 199 134 128 93 75 47 37

23.71 65.70 17.54 5.32 28.20 172.55 3.46 2.58 5.03 0.19 0.44 0.87 10.52 2.13 0.99 0.78 1.52

0.38 3.56 1.75 1.05 5.45 3.06 0.68 7.13 3.56 0.46 3.11 1.41 9.05 3.05 5.35 49.12 28.09

507 467 457 431 397 379 297 278 259 234 206 136 121 97 82 50 36

488 449 439 414 381 364 285 267 249 225 198 131 117 93 79 48 34

13.74 89.55 3.62 5.40 99.32 51.22 2.94 2.41 4.17 0.12 0.46 0.54 8.13 1.74 1.18 0.80 1.25

0.5 1.6 3.13 1.01 2.73 2.33 0.55 4.15 1.81 0.38 2.92 2.59 9.7 2.15 6.75 30.38 31.11

dC3N2C6C7(51) dC3N2C6(29) + sH22O5C1C3(21) tC9N12(12) + dC1C3N2(15) + cC1C3N2C6(16) dC10N11C6C7(69) dC3N2C6(13) + sH22O5C1C3(56) tN12C9(10) + dCCC(38) pyr.ring + sH22O5C1C3(13) dCCC(11) pyr.ring + cC4C3N2C6(17) dN2C6C7C8(48) dC9N2C13(40) + dC8C9N12(14) + dH15C1C3C4(11) dH15C1C3C4(81) dC9N2C4(17) + dCCC(19) pyr.ring + dC10C9C12(28) dC9N12O13(11) + dC6N2C3(37) + dC4C3C1O5(16) dC4C3C1O5(55) dC4C3C1O5(21) + dC1C3N2C6(26) + dC3N2C6(18) dC10C9N12O13(71) + dC1C3N2C6(13) dC10C9N12O13(13) + dC1C3N2C6(68) dC4C3C1O5(12) + dC4C3N2C6(60)

CH2 vibrations The C–H stretching of the methylene groups are at lower frequencies than those of the aromatic C–H ring stretching. The CH2 antisymmetric stretching vibrations are generally observed in the region 3000–2900 cm1, while the CH2 symmetric stretching will appear between 2900 and 2800 cm1 [42,43]. No bands are observed for the CH2 asymmetric stretching vibrations in FT-IR and FT-Raman spectrum for our title molecule. We predicted the wavenumbers at 2973 cm1 in B3LYP method and 2931 cm1 in HF method are assigned to antisymmetric stretching vibrations as shown in Table 2. CH2 symmetric stretching vibration observed at 2801 cm1in FTIR spectrum. The theoretically computed wavenumbers at 2876 cm1 in dft method and 2858 cm1in HF method. The TED corresponding to symmetric type of vibrations shows a pure mode of above 90% respectively. In the present assignment the CH2 bending modes follow, in decreasing frequency, the general order CH2 deformation > CH2 wagg > CH2 twist > CH2 rock. Since the bending modes involving the hydrogen atom attached to the central carbon atom falls in the 1450–875 cm1 range, there is extensive vibrational coupling of these modes with CH2 deformations, particularly with the CH2 twist. Contreras et al. [44] assigned at 1438 cm1 (IR) and 1438 cm1 (Raman) and Ramaekers et al. [45] assigned at 1447 cm1 for the bending vibrations. For our title molecule, the CH2 bending mode has been observed at 1458 cm1 in IR spectrum. The theoretically predicted wavenumbers at 1454 cm1 and 1474 cm1 by DFT and HF methods respectively are assigned CH2 bending vibrations. In our title molecule the scaled vibrational frequencies computed by B3LYP method at 1448 cm1 and 1469 cm1 by HF method is assigned to CH2 scissoring modes of CH2 unit. The calculated TED corresponding to this mode is also as a mixed mode with 72% of CH2 scissoring mode. The computed wavenumber at 1364 and 1377 cm1 in B3LYP method and 1411 and 1417 cm1 in HF method were assigned to CH2 rocking vibration for our title molecule. The calculated TED corresponding to this mode is a mixed mode with 70% of CH2 rocking mode. CH3 vibrations Two asymmetric and one symmetric stretching vibrations of CH3 group are usually observed in the range 2990–2950 cm1 [46,47]. In the present case of our molecule, the asymmetric stretching vibrations of CH3 group have been identified at 2997 and 3014 cm1 by B3LYP method 2945 and 2954 cm1 cm1 by HF method. The asymmetric stretching vibrations of CH3 group have been identified at 2927 in DFT method 2875 cm1 in HF method. No symmetric and asymmetric stretching bands observed in the FTIR and FT-Raman spectrum of methyl group. The in-plane bending vibration of the CH3 group is identified at 1460 cm1 in FT-Raman spectrum and 1481 cm1 in FTIR spectrum. The computed wavenumbers at 1456 cm1 in B3LYP method 1482 cm1 in HF method is assigned to in-plane bending of the CH3 group. NO2 vibrations The most characteristics bands in the spectra of nitro compounds are due to NO2 stretching vibrations, which are the two most useful group wave numbers, not only because of their spectral region but also for their strong intensity [48]. The asymmetric and symmetric stretching vibrations of NO2 group generally give rise to bands in the regions 1500–1570 cm1 and

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1300–1370 cm1 in nitrobenzene and substituted nitrobenzenes [49,50], respectively. In our study the weak symmetric stretching mode observed at 1351 cm1 in FT-Raman spectrum. The calculated wavenumbers at 1348 and 1336 cm1 in B3LYP method and 1371 and 1401 cm1 in HF method assigned to symmetric stretching vibration of NO2 group. The observed wavenumber at 1351 cm1 in FT-Raman spectrum for symmetric stretching mode is good agreement with the calculated values at 1348 cm1 by B3LYP method. The asymmetric stretching vibrations observed at 1583 cm1 in FT-Raman spectrum. The predicted wavenumbers at 1534, 1582 and 1591 cm1 in DFT method and 1590, 1623 and 1670 cm1 HF method assigned to asymmetric stretching vibration of NO2 group .The in-plane bending modes are calculated at 664, 793 and 838 cm1 by B3LYP method and 675, 809 and 867 cm1 by HF method and this mode is observed at 697 and 761 cm1 in FT-IR spectrum. The TED corresponding to this vibration suggests that it is a very weak mode and exactly contributing to 34%. Pyridine ring vibrations Vibrations of the pyridine ring are well known and described in the literature [51,52]. Also the pyridine ring vibrations of 2-aminopyridine, 2-aminopicoline [53], 2-amino-6-methylpyridine [54] 4-N,N-dimethylaminopyridine [55], 2-amino-4nitro and 2-aminonitro pyridine [56] were analyzed earlier. Therefore, the assignment of the pyridine ring vibrations in title molecule is relatively uncomplicated because they are observed at very characteristic wavenumbers. The ring stretching vibration (C–H) bands are centered usually on 3090–3020 cm1 [55]. The symmetric C–H stretching vibrations of pyridine ring appear at 3073 cm1 in FT-Raman spectra. The calculated wavenumbers at 3089 cm1 in B3LYP method 3073 cm1 in HF method assigned to C–H symmetric stretching vibration of pyridine ring. Also the calculated wave numbers at 3105 cm1 B3LYP method and 3076 cm1 in HF method assigned to C–H symmetric stretching vibration of pyridine ring. The TED corresponding to this vibration suggests that it is a very strong mode and exactly contributing to 99%. The in-plane bending vibrations are usually coupled with the pyridine (C–C) stretching mode appear in the following regions: 944, 1399 and 1419 cm1 in DFT method and 1002, 1450 and 1465 cm1 in HF method. It is also observed at 1405 cm1 in FTIR spectrum. The in-plane bending vibrations are observed at 622, 761 cm1 in FTIR spectrum and 637 cm1 in the FT-Raman spectrum. The computed wavenumber at 198, 285, 621, 793 and 986 cm1 in B3LYP method and 199, 292, 628, 803 and 1022 cm1 in HF method. The calculated value by the B3LYP method is good agreement with experimental findings. NBO analysis In NBO analysis, the input atomic orbital basis set is transformed via natural atomic orbitals and natural hybrid orbitals into natural bond orbitals. The NBOs obtained in this fashion correspond to the widely used lewis picture, in which two-center bonds and lone pairs are localized [57]. The Natural Bond Orbitals (NBOs) calculations were performed using NBO 3.1 program [58] as implemented in the Gaussian 03 package at the DFT/B3LYP level in order to understand various second-order interactions between the filled orbitals of one subsystem and vacant orbitals of another subsystem. In the NBO analysis, the electronic wave functions are interpreted in terms of a set of occupied Lewis and a set of non-Lewis localized orbitals [59]. Delocalization effects can be identified from the presence of off diagonal elements of the Fock matrix in the NBO basis. The output obtained by the 2nd-order perturbation theory analysis is normally the first to be examined by the experienced NBO user in searching for significant delocalization effects. However, the strengths of these delocalization interactions, E(2), are

estimated by second order perturbation theory [60] as estimated by Eq. 2

E2 ¼ DEij ¼ qi

Fði; jÞ ej  ei

qi is the donor orbital occupancy; Ei, Ej is the diagonal elements and Fij is the off diagonal NBO Fock matrix element. In this present work the p electron delocalization is maximum around N11–C6, C7–C8, C9–C10 distributed to p antibonding of C9–C10, C9–N11, N12–O4 with a stabilization energy of about 34.57 kJ/mol, 28.64 kJ/mol, 29.63 kJ/mol shown in Table 3. The most important interaction energy in this molecule is r electron donating from LP(1) N11 ? r(C6–C7), r(C9–C10) resulting a stabilization energy of about 10.59 kJ/mol, 9.83 kJ/mol respectively. In title molecule, the other most important interaction energy, is electron donation from rLP(1) N2 to the antibonding acceptor p(C6– N11) orbital with the stabilization energy of about 49.75 kJ/mol and r(C10–H25) ? p(C6–N11) with the stabilization energy of about 5.10 kJ/mol. The appreciable high interaction energy were observed for LP(2) O3 ? r(N12–O14), r(C9–N12) with the stabilization energy of about 19.17 kJ/mol, 11.87 kJ/mol respectively and LP(3) O13 ? p(N12–O14) with the stabilization energy of about 160.32 kJ/mol. The interaction energy observed p donar and p acceptor is p(C6–N11) ? p(C9–C10), p(C7–C8) with energy of about 146.74 kJ/mol, 95.92 kJ/mol respectively and p(N12–O14) ? p(C9–C10) with energy of about 19.70 kJ/mol. These molecular charge transfer (r ? r, p ? p) can induce large non-linearity of the molecule. 13

C and 1H NMR spectral analysis

The molecular structure of SN5N2PLA is optimized by using B3LYP method with 6-31G(d, p) as a basis set. Then, gauge invariant atomic orbital (GIAO) 1H and 13C calculations of S-2-5N2PYA1PL are calculated and compared with experimental data, which are shown in Table 4. The 1H and 13C NMR spectra are presented in supplementary materials S2 and S3. The result shows that the range of 1H and 13C NMR chemical shift of the typical organic molecule is usually > 100 ppm [61,62] the accuracy ensures reliable interpretation of spectroscopic parameters. In the present work, 13C NMR chemical shifts in the ring for the title compound are >100 ppm, as they would be expected (Table 4). The oxygen and nitrogen atoms polarize the electron distribution in its bond to carbon and decrease the electron density at the ring carbon. Therefore, the chemical shifts values of C9 bonded with the nitrogen atom shows too high which is observed at 131.64 ppm (C–N) and calculated 129.46 ppm in methanol solution. Two oxygen atoms of the nitro group have similar negative charges that are compensated through the positive charges on the nitrogen and C9 atoms. The nitrogen of the nitro group and C9 carbon of the pyridine ring are bounded via the single C–N bond. Similarly, other three carbons peaks in the ring are observed from 64.84 to 134.86 ppm and are calculated from 62.78 to 137.60 ppm. The important aspect is that, hydrogen attached or nearby electron withdrawing atom or group can decrease the shielding and move the resonance of attached proton towards to a higher frequency. By contrast electron donating atom or group increases the shielding and moves the resonance towards to a lower frequency. The chemical shift values of H atoms are measured in the range 1.26–8.90 ppm and calculated in the range 1.70– 8.93 ppm. In this present study, the chemical shifts obtained at 1.26 and calculated at 1.70 ppm for the hydrogen atom H22 of Hydroxyl groups are quite low (63 ppm) due to the shielding effect. Due to the electron withdrawing (NO2) environmental, the protons H23 and H24 chemical shifts are high which is observed

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K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 Table 3 Second order perturbation theory analysis of Fock matrix in NBO basis for (S)-()-N-(5-Nitro-2-pyridyl) alaninol. Donor (i)

ED (i)(e)

p(C6–N11) p(C7–C8)

1.662 1.715

r(C10–H25) p(N12–O14) p(C9–C10)

1.979 1.986 1.635

LP(1) N11

1.914

LP(1) N2 LP(2) O3

1.724 1.900

LP(3) O13 LP(2) O14

1.459 1.900

p(C6–N11)

0.474



p (C7–C8)

0.265

p(C9–C10) p (N12–O14)

0.374 0.649

p(N12–O14)

0.649

Acceptor (j) 

p (C9–C10) p(C9–N11) p(C9–C10) p(C6–N11) LP(3) O13 p(N12–O4) p(C7–C8) p(C6–N11) r(C6–C7) r(C9–C10) p(C6–N11) r(N12–O14) r(C9–N12) p(N12–O14) r(N12–O13) r(C9–N12 p(C9–C10) p(C7–C8) RY(3) C7 RY(5) C8 RY(5) C10 RY(3) N12 RY(2) O14 RY(9) N12 RY(2) O13 p(C9–C10)

ED (j)(e)

E(2)a kJ mol1

E(j)–E(i)b a.u.

F(i, j)c a.u.

0.374 0.474 0.374 0.023 1.460 0.649 0.265 0.474 0.035 0.032 0.474 0.057 0.097 0.649 0.057 0.097 0.374 0.265 0.001 0.000 0.001 0.008 0.002 0.000 0.002 0.374

34.57 28.64 13.64 5.10 11.71 29.63 24.79 11.93 10.59 9.83 49.75 19.17 11.87 160.32 19.29 11.84 146.74 95.92 1.93 1.86 2.53 3.85 3.46 1.22 1.19 19.70

0.32 0.26 0.28 1.03 0.17 0.15 0.29 0.26 0.87 0.90 0.26 0.70 0.59 0.14 0.70 0.59 0.02 3.03 0.68 0.99 0.66 2.12 1.12 1.07 1.12 0.13

0.094 0.081 0.057 0.065 0.077 0.065 0.078 0.051 0.087 0.085 0.107 0.105 0.075 0.138 0.105 0.075 0.081 0.081 0.089 0.105 0.084 0.141 0.097 0.057 0.057 0.063

ED means electron density. a E(2) means energy of hyper conjugative interactions. b Energy difference between donor and acceptor i and j NBO orbitals. c F(i, j) is the Fock matrix element between i and j NBO orbitals.

Table 4 The observed (Methanol) and predicted 1H and

13

C NMR isotropic chemical shifts (with respect to TMS, all values in ppm) for (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

Atom position

Experimental (Methanol)

B3LYP/6-31G(d, p)

Atom position

Experimental (Methanol)

B3LYP/6-31G(d, p)

C1 C3 C6 C7 C9 C10 – –

64.84 – – 107.81 131.64 134.86 – –

62.78 49.32 152.98 96.06 129.46 137.60 – –

H15 H16 H18 H19 H21 H22 H23 H24

3.33 3.58 3.61 – – 1.26 8.09 8.90

3.34 3.50 3.69 0.99 0.76 1.70 8.19 8.93

at 8.09 and 8.90 ppm calculated at 8.19 and 8.93 ppm. In that, we calculated chemical shifts for H15 and H16 and H18 are and 3.34 and 3.50 and 3.69 ppm also give a good correlation with the experimental observations of 3.33 and 3.58 and 3.61 ppm, respectively. Nonlinear optical (NLO) effects The NLO activity provide the key functions for frequency shifting, optical modulation, optical switching and optical logic for the developing technologies in areas such as communication, signal processing and optical interconnections [63,64]. The first static hyperpolarizability (bo) and its related properties (b, ao and Da) have been calculated using HF/6-31G(d, p) level based on finite field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field and the first hyperpolarizability is a third rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components because of the Kleinman symmetry [65]. The matrix can be given in the lower tetrahedral format. It is obvious that the lower part of the 3  3  3 matrices 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 is given below:

E ¼ Eo  la F a  1=2aab F a F b  1=6babc F a F b F cþ . . . where Eo is the energy of the unperturbed molecules, Fa is the field at the origin, la, aab and babc are the components of dipole moment, polarizability and first hyperpolarizability, respectively. The total static dipole moment l, the mean polarizability ao, the anisotropy of the polarizability Da and the mean first hyperpolarizability bo, using the x, y and z components are defined as: Dipole moment is 1=2

l ¼ ðl2x þ l2y þ l2z Þ

Static polarizability is

a0 ¼ ðaxx þ ayy þ azz Þ=3 Total polarizability is

Da ¼ 21=2 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xz  First order hyperpolarizability is

b ¼ ðb2x þ b2y þ b2z Þ

1=2

1=2

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Where

Table 6 The experimental and computed absorption wavelength k (nm), excitation energies E (eV), absorbance and oscillator strengths (f) of (S)-()-N-(5-Nitro-2-pyridyl) alaninol in methanol solution and gas phase.

bx ¼ ðbxxx þ bxyy þ bxzz Þ by ¼ ðbyyy þ byzz þ byxx Þ bz ¼ ðbzzz þ bzxx þ bzyy Þ 2 1=2

b ¼ ½ðbxxx þ bxyy þ bxzz Þ2 þ ðbyyy þ byzz þ byxx Þ2 þ ðbzzz þ bzxx þ bzyy Þ 

Since the values of the polarizabilities (a) and hyperpolarizability (b) of the Gaussian 03 output are reported in atomic units (a.u.), the calculated values have been converted into electrostatic units (esu) (For a: 1 a.u. = 0.1482  1024 esu; For b: 1 a.u. = 8.639  1033 esu). The mean polarizability ao and total polarizability Da of our title molecule are 16.1991  1024 esu and 10.7571  1024 esu respectively. The total molecular dipole moment and first order hyperpolarizability are 2.6738 Debye and 7.3759  1030 esu, respectively and are depicted in Table 5. Total dipole moment of title molecule is approximately two times greater than that of urea and first order hyperpolarizability is 20 times greater than that of urea (l and b of urea are 1.3732 Debye and 0.3728  1030 esu obtained by HF/6-311G(d, p) method). This result indicates the nonlinearity of the title molecule. Electronic properties UV–Vis spectral analysis The time dependent density functional method (TD-DFT) is able to detect accurate absorption wavelengths at a relatively small computing time which correspond to vertical electronic transitions computed on the ground state geometry, especially in the study of solvent effect [66–68]; thus TD-DFT method is used with B3LYP function and 6-31G(d, p) basis set for vertical excitation energy of electronic spectra. Calculations are performed for vacuum/gas phase, and methanol environment. The excitation energies, absorbance and oscillator strengths for the title molecule at the optimized geometry in the ground state were obtained in the framework of TD-DFT calculations with the B3LYP/6-31G(d, p) method. The theoretical and experimental maximum absorption wavelengths are compared in Table 6. The ultraviolet spectrum of the title compound is shown in Fig. 4 was measured in methanol solution. From the Table 6 TD-DFT/B3LYP method predicts one intense band in electronic transitions for the methonal solvent and gas phase at 3.563 eV (347.94 nm) and 3.825 eV (324.12 nm) with the oscillator strength 0.445 a.u. and 0.003 a.u. respectively is in good agreement with the measured experimental data in methonal at 1.1308 eV (362 nm).

Experimental

TD-DFT/B3LYP/6-31G(d, p)

Methanol

Methanol

Gas

k (nm)

E (eV)

k (nm)

E (eV)

f (a.u.)

k (nm)

E (eV)

f (a.u.)

362 – –

1.1308 – –

347.94 309.69 297.57

3.563 4.004 4.167

0.445 0.001 0.000

324.12 310.31 297.10

3.825 3.9955 4.1731

0.003 0.386 0.001

Frontier molecular orbitals Many organic molecules that contain conjugated p-electrons are characterized as hyperpolarizabilities and are analyzed by means of vibrational spectroscopy [69,70]. According to the TDDFT calculated electronic absorption spectra, the maximum absorption wave length corresponding to the electronic transition is from the HOMO to the LUMO. Energy difference between HOMO and LUMO orbital is called as energy gap that is an important stability for structures and it is a critical parameter in determining molecular electrical transport properties [71,72]. The plots of HOMO and LUMO are shown in supplementary material S4. This electronic absorption corresponds to the transition from the ground state to the first excited state and is mainly described by one electron excitation from HOMO to LUMO. While the energy of the HOMO is directly related to the ionization potential, LUMO energy is directly related to the electron affinity. In addition, According to B3LYP/6-31G(d, p) calculation, the energy band gap of the molecule is about 4.2431 eV. The HOMO orbitals are localized mainly on the all group of the molecule. On the other hand, the LUMO orbitals are localized mainly on (5-Nitro-2-pyridyl) group and exception of methyl and hydroxyl group.

HOMO energy ¼ 6:3907 eV LUMO energy ¼ 2:1476 eV HOMO  LUMO energy gap ¼ 4:2431 eV

Atomic charges Mulliken atomic charge calculation [73] has an important role in the application of quantum chemical calculation to molecular system. The mulliken atomic charges are calculated at B3LYP/631G(d, p) level by determining the electron population of each atom as defined by the basis function shown in supplementary material S5. The carbon atoms C6 (0.476) have the highest positive charge when compared with all other carbon atoms as shown in

Table 5 The electric dipole moment, polarizability and first order hyperpolarizability of (S)-()-N-(5-Nitro-2-pyridyl) alaninol by HF/6-31G(d, p) method. Dipole moment, l (Debye)

Polarizability a

Parameter

Value (DB)

Parameter

a.u.

esu (1024)

Parameter

a.u.

esu (1033)

lx ly lz l

0.8966 1.8606 1.6981 2.6738

axx axy ayy axz ayz azz ao Da

69.8448 10.1310 128.2290 24.2430 26.1792 129.8425 109.3054 72.5856

10.3510 1.5014 19.0035 3.5928 3.8798 19.2427 16.1991 10.7571

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz btot

28.9345 18.1449 146.2773 213.4871 1.2755 126.4022 431.0851 11.0487 389.9730 138.6719 853.7888

249.9651 156.7538 1263.6896 1844.3151 11.0190 1091.9886 3724.1442 95.4497 3368.9767 1197.9865 7375.8814

First order hyperpolarizability b

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hardness (g), chemical potential (l), softness (S), electronegativity (v) and electrophilicity index (x) have been defined [78,79]. On the basis of EHOMO and ELUMO, these are calculated using the below equations. Using Koopman’s theorem for closed-shell molecules, The hardness of the molecule is

g ¼ ðI  AÞ=2 The chemical potential of the molecule is

g ¼ ðI þ AÞ=2 The softness of the molecule is

S ¼ 1=2g Fig. 4. The UV–Visible spectrum (Methanol) of (S)-()-N-(5-Nitro-2-pyridyl) alaninol.

the histogram supplementary material S6. Due to the reason this carbon atom is bonded to N atom of the donor NH group. Moreover, hydrogen atoms connected to oxygen atom have the maximum positive charges H22 (0.315), at the DFT calculation this is due to the reason of electro negative Oxygen of the OH group. The NH group of Nitrogen atom N2 (0.558) have the bigger negative charges compare to all other Nitrogen atoms in the molecule. Nitrogen atom of the nitro group has large positive charge value N12 (0.366). This is due to the presence of electronegative oxygen atom in the nitro group. The OH group Oxygen atom have the highest negative charge O5 (0.537) compare other Oxygen atoms O13 (0.408) and O14 (0.409) in the nitro group of the title molecule. Molecular electrostatic potential (MEP) MEP is related to the electronic density and is a very useful descriptor in understanding sites for electrophilic and nucleophilic reactions as well as hydrogen bonding interactions [74]. The molecular electrostatic potential, V(r) is related to the electronic density and is a very useful descriptor for determining sites for electrophilic attack and nucleophilic reactions as well as hydrogen bonding interaction [75,76]. MEP values were calculated using following the equation [77]:

VðrÞ ¼

X

ZA=jRA  rj 

Z

qðr0 Þ=jr0  rjd3r0

where ZA is the charge of nucleus A located at RA, q(r’) is the electronic density function of the molecule, and r’ is the dummy integration variable. To predict reactive sites for electrophilic and nucleophilic attack for the title molecule, MEP was calculated at the B3LYP/6-31G(d, p) optimized geometry as shown in supplementary material S7. The different values of the electrostatic potential represented by different colors; red represents the regions of the most negative electrostatic potential, white represents the regions of the most positive electrostatic potential and blue represents the region of zero potential. The color code of these maps is in the range between 0.0500 (deepest red) and +0.0500 (white) in the title compound, where white indicates the strongest attraction and red indicates the strongest repulsion. According to these calculated results, the MEP map shows that the negative potential sites are on oxygen atoms as well as the positive potential sites are around the hydrogen atoms. The negative (red color) regions of MEP were related to electrophilic reactivity and the positive (white color) ones to nucleophilic reactivity. Global reactivity descriptors By using HOMO and LUMO energy values for a molecule, the global chemical reactivity descriptors of molecules such as

The electronegativity of the molecule is

v ¼ ðI þ AÞ=2 The electrophilicity index of the molecule is

x ¼ l2 =2g where A is the ionization potential and I is the electron affinity of the molecule. I and A can be expressed through HOMO and LUMO orbital energies as I = EHOMO and A = ELUMO. The ionization potetional A and an electron affinity I of our molecule SN5N2PLA calculated by B3LYP/6-31G(d, p) method is 2.1476 and 6.3907 respectively. The calculated values of the Hardness, Softness, Chemical potential, Electronegativity and Electrophilicity index of our molecule is 2.1216, 4.2432, 4.2692, 4.2692 and 4.2954 respectively as shown in supplementary material S8. Considering the chemical hardness, large HOMO–LUMO gap represent a hard molecule and small HOMO–LUMO gap represent a soft molecule. Thermodynamic properties Based on the vibrational analysis of our title molecule at B3LYP6-31G(d, p) basis set, the thermodynamic parameters such as Heat capacity (C0p,m), entropy (S0m) and enthalpy (H0m) were calculated using perl script THERMO.PL [80] and are listed in Supplementary material S9. From the Supplementary material S9 it can be seen that, when the temperature increases from 100 to 1000 K the thermodynamic functions (C0p,m, S0m, H0m) are also increases, because molecular vibrational intensities increase with temperature [81]. Fitting factor (R2) of the thermodynamic functions such as heat capacity, entropy and enthalpy changes are 0.978, 0.967 and 0.976 respectively. The correlation graphics of temperature dependence of thermodynamic functions for SN5N2PLA molecule are shown in Supplementary material S10. Vibrational zero-point energy of the SN5N2PLA is 521.43 kJ/mol. Conclusion The FT-IR, FT-Raman spectra, 1H, 13C NMR and UV–Visible spectra of (S)-()-N-(5-Nitro-2-pyridyl) alaninol have been recorded and analyzed. The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments of title molecule have been calculated using HF and B3LYP method with 6-31G(d, p) as basis set. Comparison of the experimental and calculated spectra of the molecule showed that DFT-B3LYP method is in good agreement with experimental data. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The UV spectrum was measured in methanol solution and results are compared with theoretical results. The NBO analysis revealed that the LP(3) O13 ? p(N12–O14) interaction gives the strongest stabilization to the system around at 160.32 kJ/mol. The lowering of the HOMO ? LUMO energy gap

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explains the charge transfer interaction takes place within the molecule. The 1Hand 13C NMR magnetic isotropic chemical shifts were calculated by B3LYP/6-31G(d, p) basis set and compared with experimental findings. The MEP map shows that the negative potential sites are on oxygen atoms as well as the positive potential sites are around the hydrogen atoms. The greater dipole moment and hyperpolarizability of the title molecule shows the large NLO optical property of the title molecule. The chemical hardness, chemical softness and electrophilicity index of the SN5N2PLA molecule are calculated. The thermodynamic properties (heatcapacity, entropy and enthalphy) in the temperature range from 100 to 1000 K also calculated. Acknowledgement The authors are thankful to Dr. N. Sundaraganesan, Professor of physics, Annamalai University, Tamilnadu, India for providing Gaussian 03W facility. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.02.107. References [1] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York, 1987. [2] P.N. Prasad, D.J. Williams, Introduction to Nonlinear Optical Effects in Organic Molecules and Polymers, Wiley, New York, 1991. [3] J.L. Oudar, D.S. Chemla, J. Chem. Phys. 66 (1977) 2664–2668. [4] J.L. Oudar, J. Chem. Phys. 67 (1977) 446–457. [5] A.A. Kaminskii, T. Kaino, T. Taima, A. Yukoo, K. Ueda, K. Takaichi, J. Hulliger, H.J. Eichler, J. Hanuza, J. Fernandez, R. Balda, M. Maczka, G.M.A. Gad, Jpn. J. Appl. Phys. 41 (2002) L 603–L 605. [6] M.K. Marchewka, M. Drozd, J. Janczak, Spectrochim. Acta Part A 79 (2011) 758– 766. [7] Tatsutoshi Kanetake, Makoto Otomo, Analytical Sciences, vol. 4, August 1988, pp. 411–415. [8] K. Kohatha, Yoshiaki Kawamonzen, Tsugikatsu Odashima, Hajime Ishii, Bull. Chem. Soc. Jpn. 63 (12) (1990) 3398–3404. [9] Chan-il Park, Hyun-Soo Kim, Ki-Won Cha Bull, Korean Chem. Soc. 20 (3) (1999) 352–354. [10] D. Sajan, J. Binoy, B. Pradeep, K. Venkatakrishnan, V.B. Kartha, I.H. Joe, V.S. Jayakumar, Spectrochim. Acta A 60 (2004) 173–180. [11] J.P. Abraham, I.H. Joe, V. George, O.F. Nielson, V.S. Jayakumar, Spectrochim. Acta A 59 (2003) 193–199. [12] P.S. Kushwaha, P.C. Mishra, Int. J. Quant. Chem. 76 (2000) 700–713. [13] Gaussian Inc., Gaussian 03 Program, Gaussian Inc., Wallingford, 2004. [14] H.B. Schlegel, J. Comput. Chem. 3 (1982) 214–218. [15] A. Frisch, A.B. Nielson, A.J. Holder, Gaussview User Manual, Gaussian Inc., Pittsburgh, PA, 2000. [16] M.H. Jamróz, Vibrational Energy Distribution Analysis VEDA 4, Warsaw, 2004. [17] N.C. Handy, P.E. Maslen, R.D. Amos, J. Phys. Chem. 97 (1993) 4392–4396. [18] V. Krishnakumar, R. Mathammal, S. Muthunatesan, Spectrochim. Acta 70A (2008) 210–216. [19] R. Ditchfield, J. Chem. Phys. 56 (1972) 5688–5691. [20] K. Wolinski, James F. Hinton, P. Pulay, in: J. Am. Chem. Soc. 112 (1990) 8251– 8260. [21] N. Azizi, A.A. Rostami, A. Godarzian, J. Phys. Soc. Jpn. 74 (2005) 1609–1620. [22] M. Rohlfing, C. Leland, C. Allen, R. Ditchfield, Chem. Phys. 87 (1984) 9–15. [23] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version3.1, TCI, University of Wisconsin, Madison, 1998. [24] G. Kereztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta 49A (2007–2017) (1993) 2019–2026. [25] G. Kereztury, in: J.M. Chalmers, P.R. Griffith (Eds.), Raman Spectroscopy: Theory, Hand Book of Vibrational Spectroscopy, vol. 1, John Wiley & Sons Ltd, New York, 2002. [26] V.H. Rodrigues, M.M.R.R. Costa, T. Dekola, E. de Matos Gomes, Acta Cryst. E65 (2009) m1000. ISSN 1600-5368. [27] N. Sundaraganesan, G. Mariappan, S. Manoharan, Spectrochim. Acta A 87 (2011) 67–76. [28] H. Lampert, W. Mikenda, A. Karpten, J. Phys. Chem. 101 (1997) 2254–2263. [29] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identification of Organic Compounds, fifth ed., John Wiley & Sons Inc., New York, 1981.

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