Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

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Experimental FT-IR, Laser-Raman and DFT spectroscopic analysisof 2,3,4,5,6-Pentafluoro-trans-cinnamic acid

http://dx.doi.org/10.1016/j.saa.2014.02.1221386-1425/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author at: Department of Physics, Faculty of Art & Sciences,Bozok University, Yozgat 66100, Turkey. Tel.: +90 354 2421021; fax: +90 3542421022.

E-mail address: yusufsert1984@gmail.com (Y. Sert).

Yusuf Sert a,b,⇑, Hatice Dogan a, Angélica Navarrete c, Ratnasamy Somanathan c, Gerardo Aguirre c,Çagrı Çırak d

a Department of Physics, Faculty of Art & Sciences, Bozok University, Yozgat 66100, Turkeyb Sorgun Vocational School, Bozok University, Yozgat 66100, Turkeyc Centro de Graduados e Investigación del Instituto Tecnológico de Tijuana, Apdo. Postal 1166, 22500 Tijuana, B.C., Mexicod Department of Physics, Faculty of Art & Sciences, Erzincan University, Erzincan 24100, Turkey

h i g h l i g h t s

� The FT-IR and Laser-Raman spectra ofthe title compound were recorded insolid phase.� The optimized geometry and

vibrational frequencies werecalculated for the first time.� The HOMO–LUMO energies and

related molecular properties wereevaluated.

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

a r t i c l e i n f o

Article history:Received 29 November 2013Received in revised form 4 February 2014Accepted 19 February 2014Available online 12 March 2014

Keywords:FT-IR spectraLaser-Raman spectraVibrational studyPentafluoro-trans-cinnamic acid

a b s t r a c t

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized 2,3,4,5,6-Pentafluoro-trans-cinnamic acid have been investigated. The experimental FT-IR (4000–400 cm�1) andLaser-Raman spectra (4000–100 cm�1) of the molecule in solid phase have been recorded. The theoreticalvibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have beencalculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee–Yang–Parr) andDFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemicalmethods with 6–311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignmentsof the vibrational frequencies have been done by potential energy distribution (PED) analysis by usingVEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have beenfound to be in good agreement with the corresponding experimental data, and with the results in theliterature. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupiedmolecular orbital (LUMO) energies and the other related molecular energy values have been calculatedand depicted.

� 2014 Elsevier B.V. All rights reserved.

Introduction

N-alkenyl amides are a rapidly emerging class of naturallyoccurring substances, widely distributed in higher plants, marineand microorganisms, and they exhibit an array of biological

120 Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126

properties, including antibiotic, protein kinase inhibition an antitu-mor activity [1]. In particular we are interested in the synthesis offluorinated N-alkenyl amides from commercially available fluoro-cinnamic acids and aldehydes [2]. In our synthesis of pentafluori-nated enamide, we used 2,3,4,5,6-Pentafluoro-trans-cinnamicacid as the starting material, which presents interesting propertiescritalograficas.

Literature survey reveals that to the best of our knowledge, theresults based on quantum chemical calculations, FT-IR and Laser-Raman spectral studies and HOMO–LUMO analysis on the titlecompound have not been reported. Herein, we reported detailedinterpretation of the infrared and Raman spectra based on theexperimental and theoretical results, which are acceptable andsupportable to each other. The structure of title molecule has beenalso studied by single crystal X-ray spectroscopy [3]. In this work,the theoretical and experimental studies have been performed togive a detailed definition of the optimized molecular structureand vibrational frequencies of the title molecule.

Experimental details

FT-IR spectrum (4000–400 cm�1) of the title molecule has beenrecorded by Perkin-Elmer Spectrum Two FT-IR Spectrometer witha resolution of 4 cm�1 in solid phase at room temperature. TheRaman spectrum has been recorded on Renishaw Invia Ramanmicroscope spectrophotometer in the 4000–100 cm�1 region. Theexcitation line at 785 nm has been taken from a diode laser. Itsscan number is 100, the resolution is 1 cm�1, and the sample isin solid phase.

Computational details

Density functional theory (DFT) is an approach to the electronicstructure of atoms and molecules and states that all the ground-state properties of a system are function of the charge density.So, DFT calculations cannot be considered a pure ab initio method.In DFT, the electron density is the basic variable, instead of thewave function. This reduces the computational burden of treatingelectron–electron interaction terms, which are treated explicitlyas a functional of the density. The DFT approach combines thecapacity to incorporate exchange–correlation effects of electronswith reasonable computational costs and high accuracy. The pastfew years has seen a rapid increase in the use of DFT methods indifferent types of applications, particularly since the introductionof accurate non-local corrections. In density functional theory,the exchange–correlation energy is the main issue among all ofthe approximations; therefore, the accuracy of DFT is dependeddirectly by the approximate nature of the exchange–correlationenergy functional. The DFT methods employed in the present paperare representative in aspect of the exchange–correlation energyand were commonly used in numerous theoretical studies [4–12].

The high parameterized, empirical exchange correlation func-tionals, M05-2X and M06-2X, developed by Zhao and Truhlar[13] have been shown to describe noncovalent interactions betterthan density functionals which are currently in common use. How-ever, these methods have yet to be fully bencmarked for the typesof interactions important in biomolecules. M05-2X and M06-2Xare claimed to capture ‘‘medium-range’’ electron correlation; how-ever, the ‘‘long-range’’ electron correlation neglected by thesefunctionals can also be important in the binding of noncovalentcomplex. Also, these methods have been used in numerous theo-retical studies, recently [14–20].

Initial atomic coordinates can be generally taken from any data-base or experimental XRD results. We have used the experimentalXRD data and GaussView software database to determine initial

atomic coordinates and to optimize the input structure. After theoptimization, we have used the most stable optimized structurefor other theoretical analysis. In this study, initial atomic coordi-nates that taken from GaussView database [21] have given moststable structure after optimization. The molecular structure ofthe title molecule in the ground state (in gas phase) has beenoptimized by using DFT/B3LYP and M06-2X methods with6-311++G(d,p) basis set level, and the calculated optimized struc-ture has been used in the vibrational frequency calculations. Thecalculated harmonic vibrational frequencies have been scaled by0.9614 (B3LYP) and 0.9489 (M06-2X) for 6-311++G(d,p) level,respectively [21,22]. The same scale factors were used for the en-tire spectra. The molecular geometry has not been limited, andall the calculations (vibrational wavenumbers, optimized geomet-ric parameters and other molecular properties) have been per-formed using the Gauss View molecular visualization program[21] and the Gaussian 09W program package on a computing sys-tem [23]. Furthermore, the calculated vibrational frequencies havebeen clarified by means of the potential energy distribution (PED)analysis of all the fundamental vibration modes by using VEDA 4program [24,25]. VEDA 4 program has been used in previous stud-ies by many researchers [7,12,20,26,27,11]. All the vibrationalassignments have been made at B3LYP/6-311++G(d,p) level forwhich the molecular structure is more stable. So, some assign-ments may correspond to its previous or next vibrational fre-quency value at M06-2X/6-311++G(d,p) level.

Results and discussion

Geometric structure

The single X-ray crystallographic analysis of the 2,3,4,5,6-Penta-fluoro-trans-cinnamic acid (C9H3F5O2) compound showed that itscrystal possesses space Pı and belongs to triclinic system with thefollowing cell dimensions: a = 4.3198 Å, b = 7.4921 Å, c = 13.225 Åand a = 93.612�, b = 93.912�, c = 103.769� and V = 413.37 Å3 [3].The measured density of the molecule is 1.913 mg/m3. The theoret-ical and experimental structure parameters (bond lengths and bondangles) are shown in Table 1, in accordance with the atom number-ing scheme (the optimized structure) in Fig. 1. As seen from the fig-ure, the molecule has 19 atoms. A molecule consisting on N atomshas a total of 3N degrees of freedom, corresponding to the Cartesiancoordinates of each atom in the molecule. In a nonlinear molecule, 3of these degrees belong to the rotational, and 3 to the translationalmotions of the molecule, and so, the remaining corresponds to itsvibrational motions. The net number of the vibrational modes is3N-6. Therefore, for our molecule, three Cartesian displacementsof 19 atoms provide 51 normal vibration modes. The moleculehas C1 symmetry. From Table 1 we see that the optimized parame-ters calculated at the both levels are slightly longer or shorter thanthe experimental values because the theoretical calculations corre-spond to the molecule in solid state.

The title compound, C9H3F5O2, crystallizes as OAH� � �O hydro-gen-bonded carboxylic acid dimmers that, together with CAH� � �Finteractions and O� � �F and F� � �F contacts, form a sheet-like struc-ture. These sheets are stacked via short p-p interactions. An intra-molecular CAH� � �F interaction is also observed [3].

The C7AC8 bond length is calculated as 1.343 Å (B3LYP) and1.337 Å (M06-2X). This bond length has experimentally been foundas 1.341 Å [3]. The bond length measured by Mackle and Sutton[28] and Suzuki and Kozima [29] as 1.345 and 1.336 Å, relatively.For crotonaldehyde by Jayaprakash et al. [30] this bond length isfound to be 1.323 Å/HF-6-311G(d,p), 1.342 Å/B3LYP-6-31G(d,p),and 1.338 Å B3LYP-6-311G(d,p).

The experimental value of the CAF bond lengths are changedfrom 1.330 to 1.338 Å [3]. In this study, these bond lengths are

Table 1Experimental and calculated geometric parameters of title compound.

Geometric parameters Experimental values[3] Calculated values

Bond lengths (Å) B3LYP/6-311++G(d,p) M06-2X/6-311++G(d,p)

C1AC2 1.400 1.405 1.398C1AC6 1.394 1.408 1.397C1AC7 1.461 1.459 1.463C2AC3 1.380 1.387 1.384C2AF4 1.336 1.339 1.330C3AC4 1.380 1.389 1.387C3AF5 1.338 1.335 1.325C4AC5 1.381 1.390 1.387C4AF1 1.330 1.330 1.322C5AC6 1.381 1.386 1.384C5AF2 1.330 1.335 1.326C6AF3 1.336 1.340 1.330C7AC8 1.341 1.343 1.337C7AH3 0.950 1.085 1.086C8AC9 1.474 1.478 1.484C8AH2 0.950 1.078 1.079C9AO1 1.317 1.357 1.345C9AO2 1.224 1.209 1.202O1AH1 0.840 0.969 0.966

R2 0.9791 0.9725

Bond angles (�)C2AC1AC6 115.3 115.7 116.2C2AC1AC7 119.5 118.9 118.8C6AC1AC7 125.2 125.4 125.0C1AC2AC3 122.9 122.8 122.6C1AC2AF4 119.8 119.7 119.8C3AC2AF4 117.3 117.5 117.6C2AC3AC4 119.7 119.5 119.4C2AC3AF5 120.3 120.6 120.6C4AC3AF5 120.0 119.9 119.9C3AC4AC5 119.3 119.6 119.7C3AC4AF1 120.8 120.2 120.2C5AC4AF1 119.8 120.1 120.1C4AC5AC6 120.0 119.8 119.8C4AC5AF2 119.8 119.7 119.8C6AC5AF2 120.1 120.4 120.4C1AC6AC5 122.6 122.5 122.3C1AC6AF3 120.4 120.4 120.4C5AC6AF3 116.9 117.1 117.2C1AC7AC8 127.7 128.4 127.9C1AC7AH3 116.1 115.0 115.3C8AC7AH3 116.1 116.6 116.8C7AC8AC9 119.2 119.0 118.0C7AC8AH2 120.4 123.9 124.7C8AC9AH2 120.4 117.0 117.2C8AC9AO1 112.7 110.9 111.2C8AC9AO2 123.6 126.4 125.8O1AC9AO2 123.6 122.7 122.9C9AO1AH1 109.5 107.2 107.5

R2 0.9245 0.9083

Fig. 1. The optimized molecular structure of the title compound.

Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126 121

changed as theoretically from 1.330 to 1.340 Å for B3LYP methodand from 1.322 to 1.330 Å for M06-2X method. By Quan and Sun[31] for 3-chloro-2,4,5-trifluorobenzoic acid CAF bond lengths havebeen reported 1.338, 1.349 and 1.348 Å. By Knapik et al. [32], theCAF bond lengths are found 1.342 and 1.351 Å for 2,3-difluoroben-zoic acid in X-ray study. These values are calculated 1.333 and1.345 Å for 2,3-difluorobenzoic acid and 1.338 and 1.347 Å for2,4-difluorobenzoic acid [33]. CAF bond length have been calcu-lated as 1.352 Å for 1-bromo-3-fluorobenzene by using B3LYP/6-311++G(d,p) by Mahadevan et al. [34]. For p-fluoronitrobenzeneCAF bond length value is calculated as 1.319–1.352 Å with HF,B3LYP and LSDA/6-311++G(d,p) methods by Udayakumar et al.[35]. Horton et al. [36] the C4AF1, C3AF5, C2AF4, C5AF2 andC6AF3 observed 1.334, 1.342, 1.349, 1.343 and 1.351 Å in pentaflu-oroboronic acid. The bond angle of C2AC3AC4, C3AC4AC5,C4AC5AC6, C5AC6AC1, C6AC1AC2 and C1AC2AC3 have been

Fig. 2. Comparison of observed and calculated infrared spectra of the titlecompound.

122 Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126

observed in X-ray [1] 119.7, 119.3, 120.0, 122.6, 115.4 and 122.9�,respectively. These bond angles have been calculated at 119.5(B3LYP)/119.4(M06-2X)�, 119.6(B3LYP)/119.7(M06-2X)�, 119.8(B3LYP)/119.8(M06-2X)�, 122.5(B3LYP)/122.3(M06-2X)�, 115.7(B3LYP)/116.4(M06-2X)� and 122.8(B3LYP)/122.6(M06-2X)�, respec-tively. These bond angles were observed 119.28, 119.79, 119.45,123.07, 115.3 and 123.4�, respectively, by Horton et al. [36]. TheF4AC2AC3, F4AC2AC1, F5AC3AC2, F5AC3AC4, F1AC4AC3,F1AC4AC5, F2AC5AC4, F2AC5AC6, F3AC6AC5, F3AC6AC1 bondangles have been observed 117.3, 119.8, 120.3, 120.0, 120.8,119.8, 119.8, 120.1, 116.9 and 120.4�, respectively. These bond an-gles have been calculated in this study as 117.5/117.6, 119.7/119.8,120.6/120.6, 119.9/119.9, 120.2/120.2, 120.1/120.1, 119.7/119.8,120.4/120.4, 117.1/117.2 and 120.4/120.4�, respectively withB3LYP/M06-2X methods. These bond angles have been observedfor pentafluorophenyl boronic acid [36] at 116.8, 120.14, 120.72,120.0, 120.1, 120.11, 120.2, 120.34, 117.2 and 119.74�, respectively.

H1AO1AC9 and O1AC9AO2 bond angles have been observed109.5� and 123.6�, respectively in X-ray study [3], these bond an-gles have been calculated 107.2/107.5� and 122.7/122.9� inB3LYP/M06-2X method. By Xavier et al. [37], the H1AO1AC9 bondangle have been reported as 105.46�, and by Quan et al. [31], thesebond angles have been observed at 109.5� and 123.0�, respectively.By Karabacak et al. [38], these bond angles have been reported106.5� and 121.7�, respectively in B3LYP/6-311++G(d,p).

The largest differences between the calculated (B3LYP/6-311++G(d,p)) and experimental geometries are: 0.014 Å for theC1AC6 bond, 0.135 Å for the C7AH3 bond, 0.128 Å forthe C8AH2 bond, 0.015 Å for the C9-O2 bond and 0.129 Å for theO1AH1 bond lengths; 1.1� for the C1AC7AH3 bond angle, 3.5�for the C7AC8AH2 bond angle, 3.4� for the C8AC9AH2 bond angle,1.8� for the C8AC9AO1 bond angle, 2.8� for the C8AC9AO2 bondangle and 2.3� for the C9AO1AH1 bond angles.

Vibrational analysis

The experimental FT-IR and Laser-Raman spectra of the titlecompound are compared with the selected theoretical spectra inFigs. 2 and 3, respectively. The scaled calculated harmonic vibra-tional frequencies at both B3LYP and M06-2X levels, observedvibrational frequencies, and detailed PED assignments aretabulated in Table 2. The harmonic frequencies are calculated forgaseous phase of the isolated title molecule although the experi-mental ones are obtained for its solid phase. The molecule is inter-connected by intermolecular CAH� � �F and OAH� � �O hydrogenbonds in solid phase [3]. Consequently, there is slightly disagree-ment between the observed (experimental) and the calculated fre-quencies in some modes. So, in order to introduce detailedvibrational assignments of the title molecule, the PED analysishas been carried out. All the calculated modes are numbered fromthe largest to the smallest frequency within each fundamentalwave number.

CAF vibrationsIn the fluorine compounds, very intense absorption of CF mode

occurs in the region 1100–1350 cm�1 [39,40]. Infrared spectra ofmono- and di-substituted fluorine derivatives have been studiedby Narasimhan et al. [41] and those of tri- and tetrafluorobenzeneby Ferguson et al. [42]. They have assigned the frequency at1250 cm�1 to CAF stretching mode of vibration. In analogy to theseassignments, infrared frequency observed at 1235 cm�1, is assignedas CAF stretching frequency for 1-fluoro-2,4-dinitrobenzene [43],corresponding Raman frequency for the same mode is 1246 cm�1.For 2,3-difluoro phenol, Sundaraganesan et al. [44] assigned thestrong bands at 1331 and 1279 cm�1 in FT-IR spectrum due toCAF stretching mode, and their counterpart in Raman spectrum is

at 1332 and 1280 cm�1. These bands at 1004, 1001 and 996 cm�1

were assigned as a CAF stretching vibrations for somepentafluoro-compounds [45] and pentafluoro-benzyl-bromide[46] molecule. In this study CAF stretching modes have beenobserved at 1494(IR)/1500(Ra) cm�1, 1434(IR)/1434(Ra) cm�1,1399(IR)/1420(Ra) cm�1, 1285(IR)/1292(Ra) cm�1, 1154(IR)/1134(Ra) cm�1, 1132(IR)/1134(Ra) cm�1, 1046(IR)/1134(Ra) cm�1,990(IR)/984(Ra) cm�1 and 951(IR)/957(Ra) cm�1. These bands havebeen calculated at 1475(B3LYP)/1513(M06-2X), 1454(B3LYP)/1492(M06-2X), 1377(B3LYP)/1414(M06-2X), 1273(B3LYP)/1284(M06-2X), 1121(B3LYP)/1143(M06-2X), 1102(B3LYP)/1130(M06-2X),1094(B3LYP)/1121(M06-2X), 986(B3LYP)/991(M06-2X) and941(B3LYP)/954(M06-2X)cm�1.

The CAF in-plane bending frequency appears in the region 350–250 cm�1 [47]. The CAF in-plane bending wavenumbers werecomputed by B3LYP method in the region 380–255 cm�1 for penta-flourophenyl boronic acid [48]. The band at 292 cm�1 in FT-Ramanwas assigned to CAF in-plane bending mode for 2,3-difluorophenol[44]. Sundaraganesan et al. [49] observed strong band at 759 cm�1

in FT-IR and very strong band at 750 cm�1 in FT-Raman assigned toCAF in-plane bending mode for 2-amino-4,5-difluorobenzoic acidmolecule. The CAF out-of-plane bending mode was identified asthe frequency at 590 cm�1 as a weak band in FT-IR and 592 cm�1

in FT-Raman [49]. For 2-fluorophenylboronic acid molecule, Erdog-du et al. [50] observed one band at 520 cm�1 both in the FT-IR andin the FT-Raman spectra. The CAF out-of-plane bending modes ofthe bands are supported in literature [49,51–53]. In our presentwork we predicted at 750(IR)/754(Ra), 321(Ra), 283(Ra), 278(Ra)for CAF in plane bending modes (modes no: 24, 38, 39, 40, 41)and 706(IR)/701(Ra), 627(IR)/626(Ra), 398(Ra), 351(Ra), 250(Ra),

Fig. 3. Comparison of observed and calculated Raman spectra of the titlecompound.

Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126 123

192(Ra) and 159 cm�1(Ra) (modes no: 26, 28, 29, 36, 37, 43, 45,46). The values are supported in very good agreement with theexperimental results in Table 2.

CAC (ring) vibrationsThe ring stretching vibrations are very much important and

highly characteristic of the aromatic ring itself. The ring carbon–carbon stretching vibrations occur in the region 1625–1430 cm–1.In general, the bands are of variable intensity and are observedat 1625–1590, 1590–1575, 1540–1470, 1465–1430 and 1380–1280 cm�1 from the frequency ranges given by Varsanyi [54] forthe five bands in the region. For phenylboronic acids, the aromaticCAC stretching regions were assigned in the range of 1620–1320 cm�1 in the IR spectra [55]. Similarly, the CAC stretchingmodes were recorded for 2-fluorophenylboronic acid in the rangeof 1617–1034 cm�1 [50], 3,5-dichlorophenylboronic acid in therange of 1570–969 cm�1 in FT-IR and 1584–995 cm�1 in FT-Raman[56], 3,4-dichlorophenylboronic acid at 1591–1028 cm�1 in FT-IRand 1590–1035 cm�1 in FT-Raman [57], 4 chlorophenylboronicacid 1596–1060 and 1588–1085 cm�1 in FT-IR and FT-Ramanand 4-bromophenylboronic acid at the range of 1590–1010 and1588–1004 cm�1 in FT-IR and FT-Raman, respectively [58]. In thisstudy have been observed in mode 6, 7, 8, 9, 10, 13, 16 and 21 thesemodes are agreement with experimental results as can be seen inTable 2.

The ring deformation, torsion and CCC bending modes contam-inated with other modes. The calculated wave numbers of thesemodes almost coincide with experimental data after scaling. Thering deformation, torsion and out-of-plane CCC bending modesare obtained in a large region. The TEDs of these vibrations arenot pure modes as it is evident from the second column of Table 2.

CAH and C@C (alkene) vibrationsThe CAH stretching vibrations of the alkene hydrogen are ob-

served in the region 3100–3000 cm�1 [59]. The compound underinvestigation gives rise to two CAH stretching vibrations associatedwith CAH at 3100(IR) and 3064(IR)/3069(Ra) cm�1. These modeshave been calculated at 3119(B3LYP)/3091(M06-2X) and3056(B3LYP)/3043(M06-2X) cm�1. In plane bending vibrations(dHCC) have been observed in modes 5, 11, 12, 14 and 15. Thesemodes have been calculated 1618(B3LYP)/1642(M06-2X), 1318(B3LYP)/1330(M06-2X), 1307(B3LYP)/1304(M06-2X), 1256(B3LYP)/1247(M06-2X) and 1218(B3LYP)/1207(M06-2X) cm�1. The out ofplane (sHCCO) have been observed at 1008(IR)/984(Ra) and881(IR)/887(Ra) cm�1. These modes have been calculated at993(B3LYP)/999(M06-2X), 872(B3LYP)/873(M06-2X) cm�1,respectively.

The alkene C@C stretching vibration are reported near1700 cm�1 in the literature [60]. This mode have been observedat 1626(IR)/1641(Ra) cm�1 spectrum and calculated at 1618 cm�1

in B3LYP and 1642 cm�1 in M06-2X method. The C1AC7 andC8AC9OOH vibrational modes have been observed 951(IR)/957(Ra) and 916(IR)/957(Ra) cm�1, respectively. These modes havebeen calculated at 941(B3LYP)/954(M06-2X) and 912(B3LYP)/920(M06-2X) cm�1, respectively. The out of plane vibrations(sCCCC) have been observed in mode no: 25, 43, 45, 46, 47 and48 and other related modes can be seen in Table 2.

Carboxylic acid (ACOOH) vibrationsThe vibrational bands of the terminal ACOOH groups of

2,3,4,5,6-Pentafluoro-trans-cinnamic acid contain the CAO, C@Oand OAH vibrational modes. C@O stretching band appears stronglyin the region 1870–1540 cm�1 in which the position of C@Ostretching band depends on the physical state, electronic and masseffects of neighboring substituents, conjugations and stretchingband intramolecular and intermolecular hydrogen bonding[38,61,62]. In this study these modes have been observed at1693 cm�1 in FT-IR and 1769 cm�1 in Laser-Raman spectrum.These modes have been calculated at 1719 cm�1 in B3LYP and1761 cm�1 in M06-2X methods. This result is agreement with theabove literature.

As for the AOH hydroxyl group which connects the molecules,the observed IR frequency region is usually at the interval 3550–3200 cm�1 [63]. Although these values are not observed in the re-corded IR and Raman spectra shown in Fig. 2, the OAH stretchingmode of monomer is found as 3620 cm�1 by B3LYP and3632 cm�1 by M06-2X calculation levels, as given in Table 2.Diverse dimeric units are common features among mono amino-benzoic acids as well as they are observed in the structure of ben-zoic acid [64]. It can be observed that there is a frequencydownshift of OAH stretching vibration in dimer due to the pres-ence of intermolecular interaction. In Fig. 2 the very broad contourbelow 3000 cm�1 can be observed. It comes from OH engaged invery strong hydrogen bonding.

In addition carboxylic acids also show CAO stretching band inFT-IR at about 1070 cm�1 [38]. In this study, these modes havebeen observed 1335(IR)/1319(Ra), 1132(IR)/1134(Ra), 1046(IR)/1134(Ra) and 661(IR)/701(Ra) cm�1. These modes have been calcu-lated at 1318(B3LYP)/1330(M06-2X), 1102(B3LYP)/1130(M06-2X),1094(B3LYP)/1121(M06-2X) and 666(B3LYP)/666(M06-2X) cm�1,respectively.

The carboxylic acids show in plane and out of plane bendingband of OAH 1267, 1220, 1046 and 627, 577 cm�1, respectivelyin FT-IR spectrum and 1266, 1218, 1134 and 626, 582 cm�1,respectively in Laser-Raman spectrum. These modes have been ob-served near 1179 and 549 cm�1 in FTIR spectrum for 4-butylbenzoic acid [38]. The PED calculations show that the hydroxylstretching vibrational mode is very pure. But in plane bending

Table 2Observed and calculated vibrational frequencies of th title compound with 6-311++G(d,p).

Vibration no. Assignments Observedfrequencies

Calculatedfrequencies incm�1

FT-IR Laser-Raman B3LYP M06-2X

m1 tOH(100) in the O1AH1 3620 3632m2 tCH(99) in the C8AH2 3100 3119 3091m3 tCH(100) in the C7AH3 3064 3069 3056 3043m4 tOC(81) in the C9@O2 1693 1769 1719 1761m5 tCC(55)in the C7@C8 + dHCC(17) in the H2AC8AC7/H3AC7AC8 1626 1641 1618 1642m6 tCC(63) in the ring 1626 1641 1602 1638m7 tCC(57) in the ring 1552 1531 1576 1614m8 tCC(29) in the ring + tFC(22) 1494 1500 1475 1513m9 tCC(27) in the ring + tFC(11) 1434 1434 1454 1492m10 tCC(32) in the ring + tFC(32) 1399 1420 1377 1414m11 dHOC(20) in the H1AO1AC9 + tOC(12) in the C9AO1 + dHCC(11) in the H2AC8AC9 1335 1319 1318 1330m12 dHCC(63) in the H3AC7AC8 1285 1306 1307 1304m13 tCC(33) in the ring + tFC(24) + dCCC(17) in the ring 1285 1292 1273 1284m14 tCC(33)in the ring + dHCC(15) in the H2AC8AC7/H3AC7AC8 + dHOC(12) in the H1AO1AC9 1267 1266 1256 1247m15 dHCC(43)) in the H2AC8AC7/H3AC7AC8 + dHOC(20) in the H1AO1AC9 1220 1218 1218 1207m16 tFC(37) + tCC(13) in the ring 1154 1134 1121 1143m17 tOC(42) in the O1AC9 + tFC(12) 1132 1134 1102 1130m18 tOC(27) in the O1AC9 + tFC(26) + dHOC(13) in the H1AO1AC9 1046 1134 1094 1121m19 sHCCO(91) in the H2AC8AC9AO1 out of H 1008 984 993 999m20 tFC(32) 990 984 986 991m21 tCC(25) in the ring and C1AC7 + tFC(23) 951 957 941 954m22 tCC(34) in the C8AC9 916 957 912 920m23 sHCCO(70) in the H2AC8AC9AO1 and H2AC8AC9AO2 out of H + cOCOC(14) in the O1AC9AO2AC8 881 887 872 873m24 dFCC(61) 750 754 756 754m25 cOCOC(57) in the O1AC9AO2AC8 + sCCCC(14) in the C9AC8AC7AC1 + cCCCC(13) in the ring 750 754 732 731m26 cFCCC(45) in the ring + sCCCC(13) in the ring 706 701 686 670m27 dOCO(23) in the O1AC9AO2 + tOC(15) in the O1AC9 661 701 666 666m28 cFCCC(80) in the ring 627 626 649 647m29 cFCCC(39) in the ring + sHOCC(12) in the H1AO1AC9AC8 627 626 632 632m30 dOCO(40) in the O1AC9AO2 + tFC(14) 577 582 582 586m31 sHOCC(81) in the H1AO1AC9AC8 577 582 560 572m32 tCC(29) in the C8AC9 + tFC(15) + dCCC(14) in the ring 520 503 549 557m33 dOCC(46) in the O1AC9AC8 + dCCC(14) in the C1AC7AC8 and in the ring 469 467 472 470m34 dCCC(30) in the ring and in the C1AC7AC8 + dOCC(10) in the O2AC9AC8 445 446 454 452m35 dCCC(40) in the ring 445 415 428 426m36 cFCCC(67) in the ring + cCCCC(18) in the ring 398 381 389m37 cFCCC(68) in the ring 351 376 383m38 dFCC(46) in the ring + dCCC(10) in the C8AC7AC1 321 336 337m39 dFCC(75) in the ring 283 304 303m40 dFCC(70) in the ring 278 273 270m41 dFCC(72) in the ring 278 268 264m42 dCCC(47) in the C7AC1AC2 + dOCC(12) in the O1AC9AC8 + tCC(11) in the C8AC9 250 246 246m43 cFCCC(31) in the ring + sCCCC(17) in the C1AC7AC8AC9 and in the ring 250 236 236m44 dCCC(52) in the C9AC8AC7 + tCC(17) in the C8AC9 211 201 202m45 sCCCC(54) in the C1AC7AC8AC9 and in the ring + cFCCCC(12) in the ring 192 192 194m46 sCCCC(41) in the C1AC7AC8AC9 and in the ring + sOCCC(23) in the O1AC9AC8AC7 + cFCCC(10) in the ring 159 153 153m47 sCCCC(71) in the C1AC7AC8AC9 and in the ring 127 128m48 sCCCC(56) in the C1AC7AC8AC9 and in the ring + sOCCC(29) in the O1AC9AC8AC7 123 121m49 dCCC(68) in the C8AC7AC1 80 81m50 sCCCC(54) in the C1AC7AC8AC9 + cCCCC(32)) in the C1AC7AC8AC9 51 50m51 sOCCC(23) in the O1AC9AC8AC7 + sCCCC(71) in the C1AC7AC8AC9 27 23

R2 0.9991 0.9983

t, Stretching; d, in-plane bending; c, out-of-plane bending; s, torsion.

124 Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126

vibration of hydroxyl group is overlapped with the other vibra-tions. The remainder of the observed and calculated wavenumbersand assignments of present molecule are shown in Table 2.

The correlation graphic which describes harmony between thecalculated and experimental wavenumbers is shown in Fig. 4. Ascan be seen from Fig. 4, the experimental fundamentals have goodcorrelation with B3LYP. The relations between the calculated andexperimental wavenumbers are linear and described by the follow-ing equation:

mCal ¼ 1:001mexp � 2:8113 for B3LP method

mCal ¼ 1:0023mexp þ 5:1456 for M06-2X method

We calculated R2 values (R2 = 0.9991 for B3LYP and R2 = 0.9983 forM06-2X) between the calculated and experimental wavenumbers.As a result, the performances of the B3LYP method with respectto the prediction of the wavenumbers within the molecule werequite close.

Homo–Lumo analysis

Many organic molecules containing conjugated p electronshave been characterized as hyperpolarizabilities and researchedby means of vibrational spectroscopy. The p electron cloudmoment from donor to acceptor can make the molecule highly

Fig. 4. Correlation graphics of experimental and theoretical (scaled) wavenumbersof the title compound.

Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126 125

polarized through the single-double path when it changes from theground state to the excited state. Both the highest occupied molec-ular orbital (HOMO) and the lowest unoccupied molecular orbital(LUMO) are the main orbitals taking part in chemical stability.The HOMO represents the ability to donate an electron, LUMO asan electron acceptor represents the ability to obtain an electron[56]. The LUMO and HOMO energies have been calculated byB3LYP/6-311++G(d,p) and M06-2X/6-311++G(d,p) methods, anddepicted in Fig 5. Considering the chemical hardness, large

Fig. 5. Calculated HOMO–LUMO

HOMO–LUMO gap means a hard molecule and small HOMO–LUMO gap means a soft molecule. One can also relate the stabilityof the molecule to hardness, which means that molecule with leastHOMO–LUMO gap means it is more reactive [65]. The frontier mol-ecules orbital, HOMO and LUMO and frontier orbital energy gaphelping to exemplify the reactivity and kinetic stability of mole-cules are important parameters in the electronic studies [66,67].The analysis of the wave function indicates that the electronabsorption corresponding to the transition from the ground stateto the first excited state is mainly defined by one electron excita-tion from the highest occupied orbital (HOMO) to the lowest unoc-cupied orbital (LUMO) [68].

The calculated energy of the title compound is �994.67331210a.u in B3LYP/6-311++G(d,p) and �994.32750740 a.u in M06-2X/6-311++G(d,p). Meanwhile, the lowering of the energy gap describesthat the eventual charge transfer takes place within the molecule.The HOMO–LUMO energy gap calculated at B3LYP and M06-2X/6-311++G(d,p) level reflect the chemical activity of the molecule andexplain the eventual charge transfer interaction within the mole-cule, which influences the biological activity of the molecule. Thepositive phase is represented in red color and the negative phaseis represented in green color. HOMO–LUMO plots are shown inFig. 5. As seen from the figures, the HOMO is located on theF2AC6AC5AF3 atoms and F5AC3AC2AF4. The LUMO is more fo-cused on the benzene ring, partially over the F1, F4, F3 atoms, overthe ACOOH group and HAC@CAH group.

Associated within the framework of molecular orbital theory,the ionization energy and electron affinity can be expressed byHOMO and LUMO orbital energies as I = �EHOMO and A = �ELUMO.The global hardness, g = 1/2(ELUMO � EHOMO). The electron affinitycan be used in combination with ionization energy to give elec-tronic chemical potential, l = 1/2(ELUMO + EHOMO). The global elec-trophilicity index, w = l2/2g, and softness, f = 1/g [69,70]. Theseparameters have been evaluated and tabulated in Table 3. ByKarabacak et al. [38], have been calculated HOMO–LUMO valuesand clouds. The HOMO is localized on the benzene ring, AOAC@Opart and methylene group attached to the ring and LUMO is con-tributed by the whole of the molecule without methyl group andmethylene groups. HOMO–LUMO states have been calculated andinvestigated for similar structures [33,34,37].

plots of the title compound.

Table 3Comparison of HOMO–LUMO energy gaps and related molecular properties of thetitle compound.

Molecular properties B3LYP/6-311++G(d,p) M06-2X/6-311++G(d,p)

Energies (a.u) �994.67331210 �994.32750740EHOMO (eV) �7.57326 �8.86281ELUMO(eV) �2.95735 �1.92875Energy Gap(eV) 4.61590 6.93405Ionization potential (I) 7.57326 8.86281Electron affinity (A) 2.95735 1.92875Global Hardness (g) 2.30795 3.46703Chemical Potential (l) 5.26528 5.39578Electrophilicity (w) 6.00602 4.19875Softness (f) 0.43328 0.28843Dipol moment (debye) 1.2255 1.3207

126 Y. Sert et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 119–126

Conclusion

In this study, the vibrational analysis of 2,3,4,5,6-Pentafluoro-trans-cinnamic acid molecule has been studied as experimental(FT-IR and Laser-Raman spectra) and theoretical (DFT/B3LYP andM06-2X methods). The optimized geometric parameters, vibra-tional harmonic frequencies, PED assignments, molecular orbitalenergies and other properties (related with HOMO and LUMO en-ergy values) of the compound have been calculated by usingDFT/B3LYP and M06-2X methods with 6-311++G(d,p) basis set.The theoretical optimized geometric parameters (bond lengthsand angles) and vibrational frequencies are compared with theexperimental data. Considerable level of correlation has been no-ticed. The detailed PED% analysis of the compound showed a goodagreement with the experimental data. The calculated HOMO andLUMO along with their plot has been presented for understandingof charge transfer occurring within the molecule. These results aretaken into account; we conclude that the title compound is anattractive object for future medicinal and pharmacological studies.

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