Vibrational spectroscopic, molecular structure, first hyperpolarizability and NBO studies of 4 0 -methylbiphenyl-2-carbonitrile Manpreet Kaur a , Y. Sheena Mary b , Hema Tresa Varghese b , C. Yohannan Panicker c,d,⇑ , H.S. Yathirajan a , M.S. Siddegowda a , Christian Van Alsenoy e a Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore, India b Department of Physics, Fatima Mata National College, Kollam, Kerala, India c Department of Physics, TKM College of Arts and Science, Kollam, Kerala, India d Research Centre, Department of Physics, Mar Ivanios College, Nalanchira, Trivandrum, Kerala, India e Department of Chemistry, University of Antwerp, B2610 Antwerp, Belgium highlights " IR, Raman spectra and NBO analysis were reported. " The wavenumbers are calculated theoretically using Gaussian09 software. " The wavenumbers are assigned using PED analysis. " Geometrical parameters are in agreement with XRD data. graphical abstract article info Article history: Received 27 May 2012 Received in revised form 28 July 2012 Accepted 21 August 2012 Available online 28 August 2012 Keywords: DFT Benzonitrile NBO analysis PED Hyperpolarizability abstract The FT-IR, FT-Raman spectra and XRD of 4 0 -methylbiphenyl-2-carbonitrile were recorded and analyzed. The frequencies were computed at various density functional theoretical levels using Gaussian09 soft- ware package. The data obtained from theoretical calculations were used to assign vibrational bands obtained in infrared and Raman spectra of the studied molecule. Potential energy distribution of the nor- mal modes of vibrations were done using GAR2PED program. The geometrical parameters of the title compound are in agreement with XRD crystal structure data. The first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non linear optics. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. According to XRD data, the dihedral angles between the mean planes of the two benzene rings is 44.7° and the crystal packing is stabilized by weak intermolecular p–p stacking interactions. Ó 2012 Elsevier B.V. All rights reserved. Introduction 4 0 -Methylbiphenyl-2-carbonitrile is used to synthesize various biologically active and pharmaceutical compounds viz., losartan, valsartan, candesartan, etc. [1,2]. Several benzonitrile derivatives have important applications, for example, 3-ethyl-benzonitrile for the treatment of urge urinary incontinence [3], vamicamide (a new anticholinergic agent synthesized from benzonitrile) for treatment of urge urinary incontinence [4], 3-ethyl-benzonitrile has alpha blocker properties on the cardiovascular system of rats [5], benzonitrile, 3-chlorobenzonitrole and 4-chlorobenzonitrile for the inhibition of the hydrogen absorption (corrosion) of steel, 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.08.061 ⇑ Corresponding author at: Department of Physics, TKM College of Arts and Science, Kollam, Kerala, India. Tel.: +91 9895370968. E-mail address: [email protected](C. Yohannan Panicker). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Transcript
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy
journal homepage: www.elsevier .com/locate /saa
Vibrational spectroscopic, molecular structure, first hyperpolarizabilityand NBO studies of 40-methylbiphenyl-2-carbonitrile
Manpreet Kaur a, Y. Sheena Mary b, Hema Tresa Varghese b, C. Yohannan Panicker c,d,⇑,H.S. Yathirajan a, M.S. Siddegowda a, Christian Van Alsenoy e
a Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore, Indiab Department of Physics, Fatima Mata National College, Kollam, Kerala, Indiac Department of Physics, TKM College of Arts and Science, Kollam, Kerala, Indiad Research Centre, Department of Physics, Mar Ivanios College, Nalanchira, Trivandrum, Kerala, Indiae Department of Chemistry, University of Antwerp, B2610 Antwerp, Belgium
h i g h l i g h t s
" IR, Raman spectra and NBO analysiswere reported.
" The wavenumbers are calculatedtheoretically using Gaussian09software.
" The wavenumbers are assignedusing PED analysis.
" Geometrical parameters are inagreement with XRD data.
1386-1425/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.saa.2012.08.061
⇑ Corresponding author at: Department of PhysicScience, Kollam, Kerala, India. Tel.: +91 9895370968.
The FT-IR, FT-Raman spectra and XRD of 40-methylbiphenyl-2-carbonitrile were recorded and analyzed.The frequencies were computed at various density functional theoretical levels using Gaussian09 soft-ware package. The data obtained from theoretical calculations were used to assign vibrational bandsobtained in infrared and Raman spectra of the studied molecule. Potential energy distribution of the nor-mal modes of vibrations were done using GAR2PED program. The geometrical parameters of the titlecompound are in agreement with XRD crystal structure data. The first hyperpolarizability is comparablewith the reported values of similar derivatives and is an attractive object for future studies of non linearoptics. The stability of the molecule arising from hyper-conjugative interaction and charge delocalizationhas been analyzed using NBO analysis. According to XRD data, the dihedral angles between the meanplanes of the two benzene rings is 44.7� and the crystal packing is stabilized by weak intermolecularp–p stacking interactions.
� 2012 Elsevier B.V. All rights reserved.
Introduction valsartan, candesartan, etc. [1,2]. Several benzonitrile derivatives
40-Methylbiphenyl-2-carbonitrile is used to synthesize variousbiologically active and pharmaceutical compounds viz., losartan,
ll rights reserved.
s, TKM College of Arts and
nan Panicker).
have important applications, for example, 3-ethyl-benzonitrilefor the treatment of urge urinary incontinence [3], vamicamide(a new anticholinergic agent synthesized from benzonitrile) fortreatment of urge urinary incontinence [4], 3-ethyl-benzonitrilehas alpha blocker properties on the cardiovascular system of rats[5], benzonitrile, 3-chlorobenzonitrole and 4-chlorobenzonitrilefor the inhibition of the hydrogen absorption (corrosion) of steel,
Fig. 2. Crystal Packing of 40-methylbiphenyl-2-carbonitrile.
92 M. Kaur et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99
although 2-chlorobenzonitrile increases the hydrogen absorption[6]. Benzonitrile derivatives constitute the key components of dif-ferent commercial compounds, including dyes, herbicides, agrochemicals, pesticides, natural products and pigments [7]. Boxerand co-workers [8–11] have used vibrational Stark spectroscopyto show that the stretching CN wavenumber of nitriles, especiallyaromatic nitriles, is highly sensitive to electric field in its environ-ment. Kumar et al. [12] reported the ab initio calculations, FT-IRand FT-Raman spectra of 2-chloro-6-methyl benzonitrile. The crys-tal structures of 4,40-di-methylbiphenyl-2,20-dicarboxylic acid [13],40-methylbiphenyl-2-carboxylic acid [14] and 40-(2-butyl-4-chloro-5-formylimidazol-1-ylmethyl)biphenyl-2-carbonitrile [15]were reported. Krishnakumar et al. [16] reported the IR and Ramanspectra of 2-(methylthio)benzonitrile. The importance of benzoni-trile and its derivatives have been reviewed by Palafox et al. [17].From the spectroscopic point of view, the vibrational spectra ofbenzonitrile [18–20], mono-substituted benzontriles [21,22] anddi-substituted benzonitriles [23,24] have been studied extensively,especially, the F- and Cl- benzonitrile derivatives [25–27]. Fleminget al. [28,29] reported the density functional theoretical modelingof substituted benzene and benzonitrile and Sundaraganesan etal. [30] reported the molecular structure and vibrational spectraof 3-chloro-4-fluorobenzonitrile by ab initio HF and density func-tional methods. In the present work, crystal structure data, vibra-tional spectroscopic analysis and the first hyperpolarizability of40-methylbiphenyl-2-carbonitrile is reported.
Experimental
The title compound was obtained as a gift sample from R.L. FineChem. Bangalore. X-ray quality crystals were obtained by slowevaporation of methanol solution (m.p. 323–325 K). Single crystalX-ray diffraction data of the title compound was collected in a Ox-ford Diffraction Xcalibur Eos Gemini diffractometer with Mo Ka(k = 0.71073 Å) at 173 K. Data collection and reduction were per-formed by CrysA;os PRO and SAINT/XPREP programs. The structurewas solved and refined using SIR 92 and SHELXL-97 [31]. The titlecompound crystallizes in orthorhombic P212121 with a = 7.6726 Å,b = 11.4037 Å, c = 12.2526 Å, V = 1071.19 Å3, and Z = 4. The molecu-lar structure of the title compound and its packing in the crystallattice are given in Figs. 1 and 2, respectively.
The FT-IR spectrum (Fig. 3) was recorded on a DR/Jasco FT-IR6300 spectrometer in KBr pellets. The spectral resolution was4 cm�1. The FT-Raman spectrum (Fig. 4) was obtained on a BrukerRFS 100/S, Germany. For excitation of the solid sample the Nd:YAG
Fig. 1. ORTEP diagram of 40-met
laser was used, excitation wavelength 1064 nm, maximal power150 mW. The spectral resolution after apodization was 2 cm�1.
Computational details
Calculations of the title compound were carried out with Gauss-ian09 software program [32] using the B3PW91/6-31G⁄, B3LYP/6-31G⁄ and B3LYP/SDD basis sets to predict the molecular structureand frequencies. Calculations were carried out with Becke’s threeparameter hybrid model using the Lee–Yang–Parr correlation func-tional (B3LYP) method. Molecular geometries were fully optimizedby Berny’s optimization algorithm using redundant internal coor-dinates. Harmonic vibrational wavenumbers were calculated usinganalytic second derivatives to confirm the convergence to minimaon the potential surface. The Stuttagard/Dresden effective core po-tential basis set (SDD) [33] was chosen particularly because of itsadvantage of doing faster calculations with relatively better accu-racy and structures [34]. Then frequency calculations were em-
hylbiphenyl-2-carbonitrile.
Fig. 3. FT-IR spectrum of 40-methylbiphenyl-2-carbonitrile.
Fig. 4. FT-Raman spectrum of 40-methylbiphenyl-2-carbonitrile.
M. Kaur et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99 93
ployed to confirm the structure as minimum points in energy. Atthe optimized structure (Fig. 5) of the examined species, no imag-inary frequency modes were obtained, proving that a true mini-mum on the potential surface was found. The DFT methods tendto overestimate the fundamental modes; therefore a scaling factorvalue of 0.9613 has to be used for obtaining a considerablybetter agreement with experimental data [35]. The observed dis-agreement between theory and experiment could be a conse-quence of the anharmonicity and of the general tendency of thequantum chemical methods to overestimate the force constantsat the exact equilibrium geometry. The obtained geometricalparameters are given as Supplementary material in Table S1. Thepotential energy distribution (PED) was calculated with the helpof the GAR2PED software package [36]. The assignment of the cal-culated wavenumbers is aided by the animation option of GAUSS-VIEW program, which gives a visual presentation of the vibrationalmodes [37].
Results and discussion
IR and Raman spectra
The observed IR, Raman bands and calculated (scaled) wave-numbers and assignments are given in Table 1. In esters the vibra-tions of CH3 are expected in the range 2900–3000 cm�1 [38,39].
The first of these result from asymmetric stretching tasCH3 modesin which two C–H bonds of the methyl group are extending whilethe third one is contracting and the other result from symmetricstretching tsCH3 in which all three of the C–H bonds extend andcontract in-phase. The asymmetric stretching modes of methylgroup are calculated (SDD) to be at 3017, 2991 cm�1 and the sym-metric mode at 2919 cm�1. The bands observed at 3022, 2913cm�1 in the IR spectrum and at 3022, 2991, 2916 cm�1 in the Ra-man spectrum of the title compound are assigned as CH3 stretchingvibrations. Two bending can occur within a methyl group. The firstof these, the symmetrical bending vibration, involves out-of-phasebending of the C–H bonds. The asymmetric deformations are ex-pected in the range 1400–1485 cm�1 [38]. The calculated values(SDD) of dasCH3 modes are at 1461, 1458 cm�1. Experimentallythe bands are observed at 1475 cm�1 in IR and 1472 cm�1 in Ra-man spectrum. In many molecules the symmetric deformation ds-
CH3 is expected in the range of 1380 ± 25 cm�1 [38]. Band (SDD)at 1391 cm�1 is assigned as dsCH3 mode for the title compound. Es-ters display a methyl rock in the neighborhood of 1045 cm�1 [38].The second rock in the region 970 ± 70 cm�1 [38] is more difficultto find among the C–H out-of-plane deformations. For the titlecompound, these rocking modes qCH3 are assigned (SDD) at1044, 980 cm�1. The bands at 1044 cm�1 in the IR and at 1049cm�1 in the Raman spectrum are assigned as qCH3 modes.
The geometry of the cyano (C„N) group is affected insignifi-cantly by a new substituent of the phenyl ring. Hence, the fre-
Fig. 5. Optimized geometry (SDD) of 40-methylbiphenyl-2-carbonitrile.
94 M. Kaur et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99
quency of the cyano group remains almost unchanged from thebenzonitrile molecule. For the title compound, C„N stretchingmode is assigned at 2218 cm�1 in the IR spectrum, 2223 cm�1 inthe Raman spectrum and at 2168 cm�1 theoretically (SDD). Exper-imentally, in benzonitriles [17,40] this vibration appears in the2220–2240 cm�1 range. As in benzonitrile molecule and its deriv-atives, this stretching mode appears with the strongest Ramanintensity. The intensity is enhanced by the conjugation of the phe-nyl ring. Aromatic nitriles has two bands, one band is of strongintensity in the region 580–540 cm�1 and other of medium inten-sity in the region 430–380 cm�1. The former band is due to thecombination of the out-of-plane aromatic ring deformation vibra-tion and the in-plane deformation vibration of the CN group. Thelatter band is due to the in-plane bending of the aromatic ringC–CN bond [41]. Krishnakumar et al. [16] reported C–CN bendingmodes at 580, 187, 148 cm�1. The linear bending vibration ofCCN moiety are split into in-plane and out-of-plane components,both strongly mixed with several other in-plane and out-of-planevibrations and contribute to several normal modes in the region600–100 cm�1. The deformation bands of nitrile are reported at601, 580, 411 cm�1 in IR spectrum, 602, 582, 411 cm�1 in Ramanspectrum and at 608, 587, 416 cm�1 theoretically [12]. In the pres-ent case, these bands are observed at 599, 408 cm�1 in the IR spec-trum, 413 cm�1 in the Raman spectrum and at 587, 408 cm�1
(SDD) theoretically. This is in agreement with the literature data[42,43]. In-plane and out-of-plane bending modes of C„N groupare coupled with phenyl ring deformations bands.
Since the identification of all the normal modes of vibration oflarge molecules is not trivial, we tried to simplify the problem byconsidering each molecule as substituted benzene. Such an ideahas already been successfully utilized by several workers for thevibrational assignments of molecules containing multiple homoand hetero aromatic rings [44]. In the following discussion, the1,4-substituted and 1,2-substituted phenyl rings are designatedas ring PhI and ring PhII, respectively.
The aromatic CH stretching vibrations [38] absorb between3120–3000 cm�1. The SDD calculations give bands in the range3064–3102 cm�1 for PhI and 3077–3114 cm�1 for PhII, as CHstretching modes of the phenyl rings. Experimentally, we have ob-served bands at 3084, 3056 cm�1 in the IR spectrum and at 3087,3061 cm�1 in the Raman spectrum as CH stretching modes of thephenyl rings.
The benzene ring possesses six ring stretching modes of whichthe four with the highest wavenumbers occurring near 1600, 1580,1490 and 1440 cm�1 are good group vibrations [38]. With heavysubstituents, the bands tend to shift to somewhat lower wavenum-bers and the greater the number of substituents on the ring, thebroader of the absorption regions [38]. In the case of C@O substitu-tion, the band near 1490 cm�1 can be very weak [38]. The fifth ringstretching vibration is active near 1315 ± 65 cm�1, a region thatoverlaps strongly with that of the CH in-plane deformation [38].The sixth ring stretching vibration, the ring breathing mode ap-pears as a weak band near 1000 cm�1 in mono, 1,3-di- and 1,3,5-tri-substituted benzenes. In the otherwise substituted benzenes,however, this vibration is substituent sensitive and difficult to dis-tinguish from other modes. The bands observed at 1614, 1560,1504, 1379 cm�1 in the IR spectrum, 1614, 1561, 1506, 1378cm�1 in the Raman spectrum and at 1600, 1556, 1497, 1384,1312 cm�1 (SDD) theoretically are assigned as the phenyl ringstretching modes for the 1,4-substituted benzene ring PhI. Forthe 1,2-substituted phenyl ring PhII, these modes are observed at1589, 1448, 1411, 1310 cm�1 in the IR spectrum, 1590, 1447cm�1 in the Raman spectrum and at 1581, 1540, 1454, 1415,1308 cm�1 theoretically (SDD).
The ring breathing mode for the 1,4-substituted benzenes withentirely different substituents [40] has been reported to bestrongly IR active with typical bands in the interval 780–840cm�1. For the title compound, this is confirmed by the band inthe IR spectrum at 820 cm�1, which finds support from the compu-tational results, with a high IR intensity. The ring breathing modefor 1,4-substituted benzenes are reported at 804 and 792 cm�1
experimentally and at 782 and 795 cm�1 theoretically [45,46].In the case of 1,2-disubstitution the ring breathing mode has
three frequency intervals according to whether both substituentsare heavy, or one of them is heavy while the other is light, or bothof them are light. In the first case, the interval is 1100–1130 cm�1,in the second case 1020–1070 cm�1, while in the third case it is be-tween 630 and 780 cm�1 [40]. The band observed at 1103 cm�1 inthe IR spectrum is assigned as the ring breathing mode of the phe-nyl ring PhII. The SDD calculations give this mode at 1091 cm�1.
The in-plane CH deformation bands of the phenyl ring are ex-pected above 1000 cm�1 [38]. The bands observed at 1283, 1184,1120 cm�1 (IR), 1303, 1185, 1124, 1007 cm�1 (Raman), 1300,1187, 1117, 1006 cm�1 (SDD) and 1262, 1160, 1103 cm�1 (IR),
Table 1FT-IR, FT-Raman bands and calculated (scaled) wavenumbers of 40-methylbiphenyl-2-carbonitrile and assignments.
B3PW91/6-31G⁄ B3LYP/6-31G⁄ B3LYP/SDD IR Raman Assignmentsa
t (cm�1) IR Ra t (cm�1) IR Ra t (cm�1) IR Ra t (cm�1) t (cm�1)
(SDD) are assigned as in-plane CH bending modes for the phenylrings PhI and PhII, respectively.
The out-of-plane CH deformations [38] are observed between700 and 1000 cm�1. Generally the CH out-of-plane deformationswith the highest wavenumbers are weaker than those absorbingat lower wavenumbers. The PED analysis gives the out-of-planeCH modes of the phenyl rings at 979, 957, 849, 792 cm�1 for PhIand 1002, 970, 891, 775 cm�1 for PhII ring, respectively. Experi-mentally the out-of-plane CH modes are observed at 1002, 961,884 cm�1 in the IR spectrum and at 961, 839, 802, 781 cm�1 inthe Raman spectrum. Most of the phenyl ring modes are not pure,but contains significant contributions from other modes also. Thein-plane and out-of-plane deformation modes of the phenyl ringare also identified and assigned (Table 1). The CC stretching bandsare observed at 1204 cm�1 in the IR spectrum, 1210 cm�1 in theRaman spectrum and at 1204, 1173 cm�1 (SDD) theoretically as ex-pected [38].
Geometrical parameters and first hyperpolarzability
The predicted geometrical parameters such as bond lengths,bond angles and torsion angles of the title compound calculatedat DFT levels are presented in Table S1 in accordance with the atomnumbering scheme as given in Fig. 5. When comparing experimen-tal values, the computed values are slightly different, because thetheoretical calculations are performed upon isolated molecule inthe gaseous state and the experimental results are performed onthe solid phase of the molecule.
In the case of benzene, the bond lengths between the carbonatoms held together in the hexagonal chain are almost equal. Ifso, there must be a change in bond length occurs according tothe nature of substituents. In the title molecule, the calculated C–C bond lengths (Å) of the benzene rings varies from 1.4035–1.4148 (SDD) for PhI and 1.4015–1.4267 (SDD) for PhII, whereasthe corresponding values from XRD data are, 1.3783–1.3930 and1.3773–1.4022 [31]. The outside C–C bond lengths (Å) exceeds bysmall amounts and the values are C12–C13 = 1.4915, C2–C3 = 1.4420,C18–C23 = 1.5175. The corresponding XRD values are 1.4862,1.4372 and 1.5123 Å [31]. The calculated C–H bond lengths ofthe phenyl rings and that of methyl are too long in comparisonwith the XRD results [31]. It is well known that DFT method predictbond lengths that are systematically too long, especially in C–Hbond lengths [47]. This may due to that, the low scattering factorof hydrogen atoms involved in the X-ray diffraction experimentproduces large deviation from the theoretical C–H bond lengths.
The bond angles given by SDD calculations, C10–C12–C3 = 117.4,C10–C12–C13 = 119.4, C3–C12–C13 = 123.2, C12–C3–C4 = 120.7, C12–C3–C2 = 122.3, C4–C3–C2 = 117.0, C16–C18–C19 = 117.8, C16–C18–C23 = 121.2, C19–C18–C23 = 121.0, C14–C13–C21 = 117.9, C14–C13–C12 = 120.1, C21–C13–C12 = 121.9� and the corresponding XRD val-ues [31] are in perfect agreement with these values. Thus in the ti-tle compound, the dihedral angles between the mean planes of the
two benzene rings is 44.7�. The crystal packing is stabilized byweak intermolecular p–p stacking interactions, the centroid–cen-troid distances being 3.8172 and 3.9349 Å [31].
The SDD calculations give the torsion angles, C16–C14–C13–C12 = 178.8, C14–C13–C12–C10 = �42.7, C14–C13–C12–C3 = 137.0,C19–C21–C13–C12 = �178.5, C21–C13–C12–C10 = 135.6 and C21–C13–C12–C3 = �44.7 and the corresponding XRD values are 179.3,�43.5, 135.8, �179.2, 135.2, �45.5� [31]. The C–N bond length gi-ven by XRD is 1.1370 Å [31] where as the theoretical value (SDD)shows a deviation (1.1833 Å). Zheng et al. [48] reported the CNbond length as 1.1452 Å.
Nonlinear optics deals with the interaction of applied electro-magnetic fields in various materials to generate new electromag-netic fields, altered in wavenumber, phase, or other physicalproperties [49]. Organic molecules able to manipulate photonicsignals efficiently are of importance in technologies such as opticalcommunication, optical computing, and dynamic image processing[50,51]. In this context, the dynamic first hyperpolarizability of thetitle compound is also calculated in the present study. The firsthyperpolarizability of this novel molecular system is calculatedusing B3LYP/SDD method, based on the finite field approach. Inthe presence of an applied electric field, the energy of a system isa function of the electric field. First hyperpolarizability is a thirdrank tensor that can be described by a 3 � 3 � 3 matrix. The 27components of the 3D matrix can be reduced to 10 componentsdue to the Kleinman symmetry [52]. The components of b are de-fined as the coefficients in the Taylor series expansion of the en-ergy in the external electric field. When the electric field is weakand homogeneous, this expansion becomes
E¼ E0 �X
i
liFi � 1
2
Xij
aijFiFj � 1
6
Xijk
bijkFiFjFk � 124
Xijkl
cijklFiFjFkFl þ . . .
where E0 is the energy of the unperturbed molecule, Fi is the field atthe origin, li, aij, bijk and cijkl are the components of dipole moment,polarizability, the first hyperpolarizabilities, and second hyperpo-larizibilites, respectively. The calculated first hyperpolarizability ofthe title compound is 6.68 � 10�30 esu, which is 51.38 times thatof the standard NLO material urea (0.13 � 10�30 esu) [53]. We con-clude that the title compound is an attractive object for future stud-ies of nonlinear optical properties. The root mean square (RMS)error of the wavenumbers was evaluated using the followingexpression [54].
and Raman bands are found to be 13.96, 12.42 for B3PW91/6-31G⁄, 11.63, 11.02 for B3LYP/6-31G⁄ and 10.98, 10.46 for B3LYP/SDD methods. The small differences between experimental andcalculated vibrational modes are observed. It must be due to thefact that hydrogen bond vibrations present in the crystal lead tostrong perturbation of infrared wavenumbers and intensities ofmany other modes. Moreover, we state that the experimental re-
98 M. Kaur et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 91–99
sults belong to solid phase and theoretical calculations belong togaseous phase.
NBO analysis
The natural bond orbitals (NBO) calculations were performedusing NBO 3.1 program [55] as implemented in the Gaussian09package at the DFT/B3LYP level in order to understand varioussecond-order interactions between the filled orbitals of one sub-system and vacant orbitals of another subsystem, which is a mea-sure of the intermolecular delocalization or hyper conjugation.NBO analysis provides the most accurate possible ‘natural Lewisstructure’ picture of ‘j’ because all orbital details are mathemati-cally chosen to include the highest possible percentage of the elec-tron density. A useful aspect of the NBO method is that it givesinformation about interactions of both filled and virtual orbitalspaces that could enhance the analysis of intra and inter molecularinteractions.
The second-order Fock- matrix was carried out to evaluate thedonor–acceptor interactions in the NBO basis. The interactions re-sult in a loss of occupancy from the localized NBO of the idealizedLewis structure into an empty non- Lewis orbital. For each donor (i)and acceptor (j) the stabilization energy E(2) associated with thedelocalization i ? j is determined as
Eð2Þ ¼ DEij ¼ qiðFi;jÞ2
ðEj � EiÞ
qi is the donor orbital occupancy; Ei, Ej is the diagonal elements andFij is the off diagonal NBO Fock matrix element
In NBO analysis, large E(2) value shows the intensive interactionbetween electron–donors and electron-acceptors, and greater theextent of conjugation of the whole system, the possible intensiveinteraction are given in Table S2 (Supplementary material). Thesecond-order perturbation theory analysis of Fock-matrix in NBObasis shows strong intermolecular hyper-conjugative interactionsare formed by orbital overlap between n(N) and p⁄(C–C) bond orbi-tal which result in ICT causing stabilization of the system. Theseinteractions are observed as an increase in electron density (ED)in C–C anti bonding orbital that weakens the respective bonds.There occurs a strong inter molecular hyper-conjugative interac-tion in C2–C3 from N1 of n1(N1) ? r⁄ (C2–C3) which increases ED(0.03573e) that weakens the respective bonds leading to stabiliza-tion of 14.78 kcal mol�1.
The increased electron density at the nitrogen atom leads tothe elongation of respective bond length and a lowering of thecorresponding stretching wave number. The electron density(ED) is transferred from the n (N) to the anti-bonding r⁄ orbitalof the C–C bond, explaining both the elongation and the red shift[56]. The CN stretching mode can be used as a good probe forevaluating the bonding configuration around the cyanide N atomand the electronic distribution of the benzene molecule. Thehyper-conjugative interaction energy was deduced from the sec-ond-order perturbation approach. Delocalization of electron den-sity between occupied Lewis-type (bond or lone pair) NBOorbitals and formally unoccupied (anti bond or Rydberg) non-Lewis NBO orbitals corresponds to a stabilizing donor–acceptorinteraction. Hence the 2-(4-methylphenyl) benzonitrile structureis stabilized by these orbital interactions. The NBO analysis alsodescribes the bonding in terms of the natural hybrid orbitaln1(N1), which occupy a lower energy orbital (�0.50159 a.u.) withconsiderable p-character (43.86%) and high occupationnumber(1.965 a.u.) Thus, a very poor p-type lone pair orbitalparticipates in the electron donation to the r⁄ (C–C) orbital forn1(N) ? r⁄ (C–C) interaction in the compound. The results aretabulated in Table S3 (Supplementary material).
Conclusion
The FT-IR and FT-Raman spectra of 2-(4-Methylphenyl)benzo-nitrile were studied. The molecular geometry and the wavenum-bers were calculated using DFT methods and the optimizedgeometrical parameters (SDD) are in agreement with the crystalstructure data. The small differences between experimental andcalculated vibrational modes are observed. It must be due to thefact that hydrogen bond vibrations present in the crystal lead tostrong perturbation of the infrared wavenumbers and intensitiesof many other modes. Also, we state that experimental results be-long to solid phase and theoretical calculations belong to gaseousphase. The strong inter molecular hyper-conjugative interactionin C2–C3 from N1 of n1(N1) ? r⁄ (C2–C3) which increases ED(0.03573e) that weakens the respective bonds leading to stabiliza-tion of 14.78 kcal mol�1. The increased electron density at thenitrogen atom leads to the elongation of respective bond lengthand a lowering of the corresponding stretching wave number.The RMS error of the observed IR and Raman bands are found tobe 13.96, 12.42 for B3PW91/6-31G⁄, 11.63, 11.02 for B3LYP/6-31G⁄ and 10.98, 10.46 for B3LYP/SDD methods.
Acknowledgment
C.V.A. is thankful to University of Antwerp for access to the uni-versity’s CalcUA Supercomputer Cluster.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2012.08.061.
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