научная статья по теме MOLECULAR STRUCTURE AND VIBRATIONAL SPECTRA OF ALPHA-BENZOINOXIME BY DENSITY FUNCTIONAL METHOD Физика

Текст научной статьи на тему «MOLECULAR STRUCTURE AND VIBRATIONAL SPECTRA OF ALPHA-BENZOINOXIME BY DENSITY FUNCTIONAL METHOD»

ОПТИКА И СПЕКТРОСКОПИЯ, 2014, том 116, № 2, с. 205-213

СТЕКТРОСКОПИЯ АТОМОВ И МОЛЕКУЛ

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MOLECULAR STRUCTURE AND VIBRATIONAL SPECTRA OF ALPHA-BENZOINOXIME BY DENSITY FUNCTIONAL METHOD

© 2014 n O. Dereli*, Y. Erdogdu**, M. T. Gulluoglu**, N. Sundaraganesan***, E. Turkkan*, U. Sayin****, and A. Ozmen****

*A. Kele soglu Education Faculty, Department of Physics, Necmettin Erbakan University, Meram, 42090 Konya, Turkey ** Department of Physics, Ahi Evran University, 40040 Kirsehir, Turkey *** Dept. of Physics (Engg.), Annamalai University, Annamalai Nagar, Chidambaram 608002, Tamil Nadu, India **** Department of Physics, Science Faculty, Selcuk University, Konya, Turkey E-mail: odereli@konya.edu.tr Received March 2, 2013

In the present study, an exhaustive conformational search of the Alpha-benzoinoxime has been performed. The FT-IR spectrum of this compound was recorded in the region 4000—400 cm-1. The FT-Raman spectrum was also recorded in the region 3500-50 cm-1. Vibrational frequencies of the title compound were calculated by B3LYP method using 6-311++G(d,p) basis set. The calculated vibrational frequences were analysed and compared with experimental results.

DOI: 10.7868/S0030403414020056

1. INTRODUCTION

As mentioned in our previous oxime studies [1-4], oximes and vic-dioximes are important compounds for coordination chemistry and their derivatives play significant roles as model systems especially in applied chemistry. They are used as biological model compounds (i.e., vitamin B12) and chemical building blocks for the synthesis of agrochemicals and pharmaceuticals. They are also used in photography, medicine, textiles, dye chemistry, and semiconductor manufacturing processes [5-9]. Several papers have been published on the structure of oximes and dioximes discussing the interesting property of forming complexes with transition metals [10-15]. In recent years, the findings of antitumor effects of coordination compounds in cancer research have increased the attention especially on vic-dioxime complexes [16].

Alpha-benzoinoxime (ABO) is one of the important oxime derivatives but, in the literature, we have found neither experimental data nor the calculation results on molecular structure of ABO. However, we performed a basic level conformational analysis for investigate possible model radials of gamma-irradiated ABO before [4]. It is known that, infrared and Raman spectroscopy is an efficient method to probe electronic and geometric structure of molecules, and has been widely used in studying the structural consequences. In recent years density functional theory (DFT) has become a powerful tool in the investigation of molecular structures and vibrational spectra, especially B3LYP method has been widely used [17-20]. To the best of our knowledge, neither detailed quantum

chemical calculations nor the vibrational spectra of ABO have been reported.

In the present paper, an exhaustive conformational search of the ABO has been performed. Vibrational frequencies of the title compound have been calculated by B3LYP method using 6-31++G(d,p) basis set. The calculated geometric parameters and vibrational frequencies were analyzed and compared with obtained experimental data.

2. EXPERIMENTAL

The solid form of ABO was purchased from Merck. FT-IR spectrum of solid ABO was recorded in the range 4000-400 cm-1 on Brucker IFS 66/S with PIKE Gladi ATR (Diamond) spectrometer at room temperature with 2 cm-1 resolution. The FT-Raman spectrum was recorded on a Brucker FRA 106/S spectrometer using 1064 nm excitation from a Nd:YAG laser. The detector was a Ge-diode cooled to liquid nitrogen temperature. The upper limit for wavenumbers was 4000 cm-1 and the lower wavenumber is around 50 cm-1. The measured FT-IR and FT-Raman spectra along with theoretical FT-IR spectrum are shown in Figs. 1 and 2.

3. COMPUTATIONAL DETAILS

In order to establish stable possible conformations, the conformational space of ABO was scanned with molecular mechanics method. This calculation was performed with the Spartan 08 program [21]. In the second step, geometry optimizations of the obtained possible conformations were performed with B3LYP

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Experimental

Conformer 1 1

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Conformer 2

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3600 3200 2800 2400 2000 1600 1200 800 400 0

Wavenumber, cm-1

Fig. 1. Experimental and theoretical FT-IR spectra of ABO.

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Experimental , JL j L^J^LAiuujuJi 1 1 1 1

Conformer 1 Conformer 2 _L_J 1 i. i i i i

3600 3200 2800 2400 2000 1600 1200 800 400 0

Wavenumber, cm-1

Fig. 2. Experimental and theoretical Raman spectra of ABO.

method using the standard 6-311++G(d,p) basis set. After the most stable conformer of the title compound determined, geometry optimizations and frequency calculations of this conformer have been performed by B3LYP method with 6-311++G(d,p) basis set. The optimized structural parameters were used in the vi-brational frequency calculations at the same level to characterize all stationary points as minima. In this step, all the calculations were performed using Gaussian 03 program package [22] with the default convergence criteria without any constraint on the geometry [23]. The theoretical vibrational spectra of the title compound were interpreted by means of TEDs using the SQM program [24]. It should be noted that Gaussian 03 package does not calculate the Raman intensities. The Raman activities were transformed in to Raman intensities by using Raint program [25].

4. RESULTS AND DISCUSSION 4.1. Conformational Stability and Molecular Structure

The different conformational structures of a compound are correlated with many of the physical and

chemical properties and hence their investigation is important for drug designs and to understand several medical effects. To found stable conformers, a meticulous conformational analysis was carried out for the title compound. Rotating 10° each degree intervals around the free rotation bonds, conformational space of the title compound was scanned by molecular mechanic calculation. The geometry optimizations of the obtained conformers were performed by B3LYP/6-311++G(d,p) method. Results of conformational analysis were indicated that the title compound has nine conformers as shown in Fig. 3. Ground state energies, zero point corrected energies (£'elect + ZPE), relative energies of conformers and dipole moments, were presented in Table 1. From the calculated energies of nine conformers, given in Table 1, the conformer 1 is the most stable. Zero point corrections have caused changes in the stability order of conformer 1 and conformer 2. According to the zero point corrected energies, conformer 2 is more stable than conformer 1. The difference between the total energies of the most stable conformer 1 and conformer 2 is

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Conformer 2

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Conformer 3

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Conformer 8 Conformer 9

Fig. 3. Stable conformers of ABO.

0.04 kcal/mol. This difference is 0.61 kcal/mol for zero point corrected energies. The only difference between molecular structures of these two conformers is in the orientation of oxime group and dihedrals of rings. So, both form was used in the future calculations. But it is seen in Figs. 1—2 and the Table 2 that both calculated frequencies and intensity distributions of the conformer 2 are more compatible with the experimental counterparts than those of conformer 1. The optimized geometric parameters (bond lengths, bond angles and dihedral angles) of the conformer 1 and conformer 2 were given in Table 3. The atom numbering scheme adopted in this study is given in Fig. 4.

In the literature, we have found neither experimental data nor the calculation results on molecular structure of ABO, therefore the molecular structure of the title compound is given for the first time in this study.

4.2. Vibrational Assignments

The ABO molecule has 30 atoms, which possess 84 normal modes of vibrations. All the vibrations are active in the infrared and Raman spectra. Usually the calculated harmonic vibrational wavenumbers are higher than the experimental ones, because of the an-harmonicity of the incomplete treatment of electron

Table 1. Energetics of the conformers calculated at the B3LYP/6-311++G(d,p) level

Conf. E (Hartree) AE, kcal/mol E0 (Hartree) AE0, kcal/mol Dip. Mom. (D)

1 -746.659893 0.00 -746.4185970 0.61 2.2615

2 -746.659824 0.04 -746.419261 0.00 2.858

3 -746.657859 1.28 -746.418438 0.79 1.0966

4 -746.657072 1.77 -746.418174 0.83 1.4296

5 -746.657018 1.80 -746.417469 0.95 0.8168

6 -746.656972 1.83 -746.417273 1.39 0.7727

7 -746.656569 2.09 -746.417205 1.56 1.6405

8 -746.655626 2.68 -746.416914 1.66 1.5647

9 -746.655026 3.05 -746.415954 2.08 1.4255

E0 — Zero point corrected energy.

Table 2. Comparison of the observed and calculated vibrational spectra of ABO

Mode nos. Experimental Theoretical

Conformer 1 Conformer 2 TEDd, %

IR Raman Scaled Freqa / TIR T c Raman Scaled Freqa Ib TIR Tc Raman

V1 3332 3417 100 2 3406 100 3 100u OH

v2 3234 3349 43 0 3307 89 1 100u OH

v3 3076 3073 3071 2 4 3076 2 3 88u CH

v4 3055 3069 5 5 3063 12 6 86u CH

v5 3064 9 5 3062 11 7 84u CH

v6 3034 3060 12 6 3055 17 1 93u CH

v7 3056 14 2 3054 16 1 92u CH

v8 3051 15 1 3046 12 2 95u CH

v9 3046 4 3 3045 5 3 90u CH

v10 3041 4 4 3038 0 1 94u CH

V11 3038 1 1 3037 1 3 93u CH

v12 2983 3033 1 1 3031 3 1 89u CH

v13 2925 2930 2954 5 3 2892 18 2 99u CH

v14 1652 1640 1632 2 9 1656 10 10 80u NC

v15 1600 1601 1592 5 4 1593 2 4 64u C=C + 17 SHCC, RingA

v16 1589 0 28 1593 0 8 62u C=C + 19 SHCC, RingA

v17 1588 1574 0 1 1578 1 1 71u C=C+ 11 SHCC, RingB

v18 1575 1576 1564 1 2 1569 1 1 64u C=C + 11 SHCC, RingA

v19 1491 1495 1480 7 2 1479 4 0 53 SHCC+ 20 SCCC, RingA

v20 1478 8 0 1478 6 0 63 SHCC+ 11 SCCC , RingB

V21 1446 1434 7 1 1439 5 0 58 SHCC + 19 u CC, RingB

v22 1428 1429 6 0 1431 3

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