Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journal homepage: www.elsevier .com/locate /saa

Vibrational spectra, NBO analysis, HOMO–LUMO and firsthyperpolarizability of 2-{[(2-Methylprop-2-en-1-yl)oxy]methyl}-6-phenyl-2,3,4,5-tetrahydro-1,2,4-triazine-3,5-dione, a potentialchemotherapeutic agent based on density functional theory calculations

http://dx.doi.org/10.1016/j.saa.2014.06.0361386-1425/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 9895370968.E-mail address: yshymamary@rediffmail.com (Y.S. Mary).

Y. Shyma Mary a,⇑, Nasser R. El-Brollosy b, Ali A. El-Emam b,c, Omar A. Al-Deeb b, P.J. Jojo d,C. Yohannan Panicker e, Christian Van Alsenoy f

a Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu, Indiab Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabiac King Abdullah Institute for Nanotechnology (KAIN), King Saud University, Riyadh 11451, Saudi Arabiad Department of Physics, Fatima Mata National College, Kollam, Kerala, Indiae Department of Physics, TKM College of Arts and Science, Kollam, Kerala, Indiaf 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 calculated

theoretically using Gaussian09software.� The wavenumbers are assigned using

PED analysis.� The geometrical parameters are in

agreement with XRD data.

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 26 April 2014Received in revised form 23 May 2014Accepted 3 June 2014Available online 14 June 2014

Keywords:TriazineFTIRFT-RamanMEPHyperpolarizability

a b s t r a c t

The experimental FT-IR and FT-Raman spectra of 2-{[(2-Methylprop-2-en-1-yl)oxy]methyl}-6-phenyl-2,3,4,5-tetrahydro-1,2,4-triazine-3,5-dione were recorded. The optimized geometric parameters, normalmode frequencies and corresponding vibrational assignments of the compound have been examined bymeans of density functional theory. Reliable vibrational assignments and molecular orbital have beeninvestigated by the potential energy distribution and natural bonding orbital analyses, respectively.The calculated first hyperpolarizability of the title compound is 2.82 � 10�30 esu which is 21.69 timesthat of the standard NLO material urea. MEP was performed by the B3LYP level and the predicted infraredintensities and Raman activities have also been reported. Quantum chemical parameters were arrivedfrom the frontier molecular orbital theory. The calculated geometrical parameters are in agreement withexperimental results. From the MEP it is evident that the negative charge covers the C@O groups and thepositive region is over the rings and NH group.

� 2014 Elsevier B.V. All rights reserved.

Fig. 1. Optimized geometry (B3LYP) of the title compound.

450 Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456

Introduction

The structural diversity and biological importance of nitrogencontaining heterocycles have made them attractive over manyyears [1–3]. Substituted 1,2,4-triazine is an important class ofnitrogen containing hetero-cycle and derivatives of 1,2,4-triazinepresent important core in many natural and synthetic compounds[4–7]. 1,2,4-Triazine-3,5(2H,4H)-diones (6-azauracils) represent animportant class of biologically-active heterocyclic compounds.Several 1,2,4-triazine-3,5-diones showed antiviral [8–10], antimi-crobial [11–14], anti-inflammatory activities [15,16], anti-malarial[17], anticancer [18–21] and antiulcer [22] activities. The title com-pound was synthesized as a potential antimicrobial agent via thereaction of bis(2-methylallyloxy)methane with silylated 6-phe-nyl-1,2,4-triazine-3,5-dione [14]. Yurdakul and Tanribuyurdu [23]reported the theoretical and experimental study of solvent effectson the structure, vibrational spectra and tautomerism of a 1,2,4-tri-azine derivative. El-Brollosy et al. [24] reported the single crystalXRD studies of the title compound. The present study describesthe electronic properties and vibrational spectra of the title com-pound (molecular formula C14H15N3O3), with the hope that theresults of present study would be helpful in future synthesis ofmore potent chemotherapeutic analogs. The energies, degrees ofhybridization, populations of the lone electron pairs of oxygen,energies of their interaction with the anti-bonding orbital of thebenzene ring and the electron density distributions and E(2) ener-gies have been calculated by NBO analysis using DFT method togive clear evidence of stabilization originating from the hyper-con-jugation of various intra-molecular interactions. There has beengrowing interest in using organic materials for nonlinear opticaldevices, functioning as second harmonic generators, frequencyconverters, electro-optical modulators etc., because of the largesecond order electric susceptibilities of organic materials. Sincethe second order electric susceptibility is related to first hyperpo-larizability, the search for organic chromophores with large firsthyperpolarizability is fully justified.

Experimental details

The title compound was synthesized according to the reportedprotocol by El-Brollosy [14]. The FT-IR spectrum (Fig. S1 supportingmaterial) was recorded using KBr pellets on a DR/JASCO FT-IR 6300spectrometer. The FT-Raman spectrum (Fig. S2 supporting mate-rial) was obtained on a Bruker RFS 100/s, Germany. For excitationof the spectrum, the emission of Nd:YAG laser was used with anexcitation wavelength of 1064 nm, a maximal power 150 mW;measurement on solid sample.

Computational details

Calculations of the title compound were carried out with Gauss-ian09 software [25] program using B3PW91/6-31G(d)(6D, 7F) andB3LYP/6-31G(d)(6D, 7F) basis sets to predict the molecular struc-ture and vibrational wavenumbers. Calculations were carried outwith Becke’s three parameter hybrid model using the Lee–Yang–Parr correlation functional (B3LYP) method. Molecular geometrieswere fully optimized by Berny’s optimization algorithm usingredundant internal coordinates. Harmonic vibrational wavenum-bers were calculated using analytic second derivatives to confirmthe convergence to minima on the potential surface. Then fre-quency calculations were employed to confirm the structure asminimum points in energy. At the optimized structure (Fig. 1) ofthe examined species, no imaginary wavenumber modes wereobtained, proving that a true minimum on the potential surfacewas found. The DFT method tends to overestimate the

fundamental modes; therefore scaling factor (0.9613) has to beused for obtaining a considerably better agreement with experi-mental data [26]. The observed disagreement between theoryand experiment could be a consequence of the anharmonicityand of the general tendency of the quantum chemical methodsto overestimate the force constants at the exact equilibrium geom-etry. The optimized geometrical parameters (B3LYP/6-31G(d)(6D,7F)) with XRD data are given in Table S1 (supporting material).The assignments of the calculated wavenumbers are aided by theanimation option of GAUSSVIEW program, which gives a visualpresentation of the vibrational modes [27]. The potential energydistribution (PED) is calculated with the help of GAR2PED softwarepackage [28].

Frontier molecular orbital refer to the highest occupied molec-ular orbital (HOMO) and the lowest unoccupied molecular orbital(LUMO). The HOMO is outermost higher energy orbital containingelectrons so it acts as an electron donor. The LUMO is the lowestenergy orbital that has the room to accept electrons so it acts asan electron acceptor. The frontier molecular orbital can offer a rea-sonable qualitative prediction of the excitation properties and theability of electron transport [29,30]. The HOMO and LUMO are alsovery popular quantum chemical parameters which determine themolecular reactivity. The energies of the HOMO and LUMO orbitalof the title compound are calculated using DFT/B3LYP method. Thenatural bond orbital calculations were performed using NBO 3.1program [31] as implemented in the Gaussian 09 package at theDFT/B3LYP level in order to understand various second order inter-actions between filled orbital of one subsystem and vacant orbitalof another subsystem. The non-linear properties have an importantrole in the design of materials used in signal processing, communi-cation technology and optical memory devices [32,33]. The firststatic hyperpolarizablity (b0) is calculated at the DFT level basedon the finite field approach. In the presence of an applied electricfield, the energy of a system is a function of the electric field andthe first hyperpolarizability is a third rank tensor than can bedescribed by 3 � 3 � 3 matrix. The 27 components of the 3Dmatrix can be given in the lower tetrahedral format and reducedto 10 components because of Kleinman symmetry [34]. The com-ponents of b0 are defined as the coefficients in the Taylor seriesexpansion of the energy in the external electric field. When theexternal electric field is weak and homogeneous, this expansionis given below:

E ¼ 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, ai, bijk and cijkl are the components of dipole moment,polarizability, the first hyperpolarizabilities, and second hyperpo-larizabilities, respectively.

Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456 451

Results and discussion

IR and Raman spectra

The observed IR and Raman bands and calculated (scaled)wavenumbers and assignments are given in Table 1. In the follow-ing discussion, the phenyl ring with mono substitution is assignedas Ph and the 1,2,4-triazine ring as Ring.

The stretching vibrations of the CH3 group are expected in therange of 2900–3050 cm�1 [35,36]. The asymmetric stretchingmodes of the methyl group are calculated to be at 3012,2956 cm�1 and the symmetric mode at 2914 cm�1. The bandsobserved at 2927 cm�1 in the IR spectrum and at 2997, 2952,2925 cm�1 in the Raman spectrum were assigned as stretchingmodes of the CH3 group. The asymmetric and symmetric bendingvibrations of the methyl group normally appear in the region of1400–1485 cm�1 and 1380–1420 cm�1 [36,37]. The bandsobserved at 1385 cm�1 in the IR spectrum and at 1452 cm�1 inthe Raman spectrum were assigned as CH3 bending modes. TheB3LYP calculations give these modes at 1462, 1451, 1383 cm�1.In the present case, the rocking modes of the methyl group werecalculated to be at 1059 and 1002 cm�1 and were observed at1048, 1001 cm�1 in the IR spectrum and at 1048, 998 cm�1 in theRaman spectrum. The torsion vibrations of methyl groups oftenwere assigned within the region 185 ± 65 cm�1 [36].

The vibrations of the CH2 group, the asymmetric stretch tasCH2,symmetric stretch tsCH2, scissoring vibration dCH2, appear in theregion 3000 ± 50, 2885 ± 45 and 1445 ± 35 cm�1, respectively[35,36]. The B3LYP calculations give tasCH2 at 3062, 3051,3051 cm�1 and tsCH2 at 2975, 2898, 2874 cm�1. The bandsobserved at 3037, 2878 cm�1 (IR) and 3066, 3040, 2974, 2902,2873 cm�1 (Raman) are assigned as asymmetric and symmetricCH2 modes, respectively. In the present case, the band observedat 1443 cm�1 in the IR, 1443, 1413 in Raman spectrum and 1473,1444, 1408 cm�1 (B3LYP) are assigned as the scissoring mode ofCH2. Bands of hydrocarbons due to CH2 twisting and waggingvibrations are observed in the region 1180–1390 cm�1 [35,38].The CH2 wagging and twisting modes are assigned at 1397, 1376,1323, 1238, 1232, 1180 cm�1 (B3LYP), 1324, 1234, 1182 cm�1

(IR), 1392, 1327, 1233 cm�1 (Raman) respectively. The bands cal-culated at 980, 957, 686 cm�1 are assigned as the rocking modesof CH2.

The carbonyl group is contained in a large number of differentclasses of compounds, for which a strong absorption band due toC@O stretching vibration is observed in the range of 1850–1550 cm�1 [37]. The carbonyl groups in the triazine fragment giverise to bands in the region of 1720–1790 cm�1 [39]. For the title com-pound, the C@O stretching bands are observed at 1715 cm�1 in theRaman spectrum and at 1745, 1727 cm�1 theoretically. For the titlecompound, as expected the asymmetric CAOAC stretching vibrationis assigned at 1109 cm�1 and the symmetric stretching mode at972 cm�1 (B3LYP) theoretically [38]. Experimentally, these modesare observed at 1108 and 975 cm�1 for the title compound. Bhagyas-ree et al. [40] reported CAOAC stretching modes at 1144, 1063 (IR),1146, 1066 (Raman) and at 1153, 1079 cm�1 theoretically.

The NH stretching vibrations give rise to bands at 3500–3300 cm�1 [41,42]. In the present study, the bands observed at3408 cm�1 in the IR spectrum, 3398 cm�1 in the Raman spectrumand 3452 cm�1 (B3LYP) were assigned as NH stretching vibration.The NAH group shows bands at 1510–1500, 1350–1250 and740–730 cm�1 [37]. According to literature, if the NAH is a partof a closed ring, the CANAH deformation band is absent in theregion 1510–1500 cm�1 [36,37]. For the title compound, theCANAH deformation band is observed at 1362 cm�1 in the Raman

spectrum and at 1359 cm�1 theoretically (B3LYP). The out of planeNH deformation is expected in the region 650 ± 50 cm�1 [36] andthe band at 679 cm�1 in B3LYP is assigned as this mode. Minithaet al. reported the tNH at 3469 cm�1, dNH at 1300 cm�1 [43].Panicker et al. reported the out-of-plane bending mode of NH at746 cm�1, theoretically [44].

The CN stretching modes are expected in the range 1100–1300 cm�1 [45]. The bands observed at 1260 cm�1 in the Ramanspectrum, 1262, 798 cm�1 in the IR spectrum and at 1397, 1256,1243, 803 cm�1 theoretically (B3LYP) are assigned as CN stretchingmodes. Panicker et al. reported the CN stretching mode at1215 cm�1 theoretically [44]. The C@N stretching modes werereported at 1535–1666 cm�1 [46], 1592 cm�1 [47] experimentallyand at 1584 cm�1 theoretically [47]. In the present study, strongpeaks at 1552 cm�1 in the Raman and 1549 cm�1 in FT-IR spectrumis identified as the C@N stretching mode of the 1,2,4-triazine ringwhich matches well with the calculated wavenumber at1545 cm�1. This is in agreement with the work of Almajan et al.[48]. B3LYP computation gives mode arising from the NAN stretch-ing at 1130 cm�1 corresponding to the peak at 1129 cm�1 inRaman spectrum. The C@C stretching mode is observed at1685 cm�1 in the IR spectrum, 1675 cm�1 in the Raman spectrumand at 1680 cm�1 theoretically (b3LYP) as expected [36,37].

The existence of one or more aromatic rings in the structure isnormally readily determined from the CAH and C@CAC ringrelated vibrations. The CAH stretching occurs above 3000 cm�1

and is typically exhibited as a multiplicity of weak to moderatebands, compared with the aliphatic CAH stretch [49]. The bandsobserved at 3123, 3099 cm�1 in the IR and 3140, 3120,3090 cm�1 in the Raman spectrum are assigned as the CAHstretching modes of the phenyl rings. The B3LYP calculations givethese modes in the range 3073–3137 cm�1.

The benzene ring possesses six ring stretching vibrations, ofwhich the four with the highest wave numbers (occurring near1600, 1580, 1490 and 1440 cm�1) are good group vibrations. Inthe absence of ring conjugation, the band near 1580 cm�1 is usu-ally weaker than that at 1600 cm�1. The fifth ring stretching vibra-tion which is active near 1335 ± 35 cm�1 a region which overlapsstrongly with that of the CH in-plane deformation and the intensityis in general, low or medium high [36]. The sixth ring stretchingvibration or ring breathing mode appears as a weak band near1000 cm�1 in mono, 1,3-di and 1,3,5-trisubstituted benzenes. Inthe otherwise substituted benzene, however, this vibration is sub-stituent sensitive and difficult to distinguish from the ring in-planedeformation.

For the title compound, the bands observed at 1579, 1492, 1429,1294 cm�1 in the IR and 1599, 1578, 1490, 1293 cm�1 in theRaman spectrum are assigned as tPh modes with 1597, 1574,1485, 1436, 1297 cm�1 as B3LYP values. For mono substituted ben-zene, the tPh modes are expected in the range of 1285–1610 cm�1

[36]. The ring breathing mode for mono substituted benzenesappears near 1000 cm�1 [36]. For the title compound, this is con-firmed by the band at 1029 cm�1 theoretically. For mono substi-tuted benzene, the in-plane CH vibrations are expected in therange of 1015–1300 cm�1 [36]. For the phenyl ring, the bandsobserved at 1310, 1165, 1022 cm�1 in the IR spectrum and at1312, 1168, 1080, 1021 cm�1 in the Raman spectrum are assignedas in-plane CH deformation modes. The B3LYP calculations alsogive these modes at 1317, 1175, 1149, 1077, 1022 cm�1 whichare in agreement with literature [36].

The CAH out-of-plane deformations cCH are observed between1000 and 700 cm�1 [36]. The cCH vibrations are mainly deter-mined by the number of adjacent hydrogen atoms on the ring.Generally, the CAH out-of-plane deformations with the highest

Table 1Vibrational assignments of 2-{[(2-Methylprop-2-en-1-yl)oxy]methyl]-6-phenyl-2,3,4,5-tetrahydro-1,2,4-triazine-3,5-dione.

B3PW91/6-31G(d) (6D, 7F) B3LYP/6-31G(d) (6D, 7F) IR Raman Assignmentsa

t IRI RA t IRI RA t t –

3471 78.15 104.73 3452 70.81 108.08 3408 3398 tNH(100)3148 8.87 54.26 3137 9.94 54.29 – 3140 tCH(99)3141 3.35 53.17 3137 3.10 50.43 – 3140 tCH(98)3109 5.28 82.03 3102 4.49 66.82 3123 3120 tCH(98)3095 27.86 2225.65 3085 32.90 244.05 3099 3090 tCH(94)3084 16.09 122.87 3073 18.83 123.90 – – tCH(95)3073 0.01 55.30 3062 0.01 57.89 – 3066 tasCH2(97)3059 10.20 122.36 3051 9.52 70.55 – 3040 tasCH2(95)3058 4.98 57.48 3051 6.97 108.27 3037 3040 tasCH2(99)3029 18.42 75.11 3012 20.12 73.49 – 2997 tasCH3(99)2977 25.15 82.29 2975 26.10 79.64 – 2974 tsCH2(100)2975 22.54 74.75 2956 27.34 77.30 – 2952 tasCH3(100)2923 29.82 138.83 2914 32.89 140.55 2927 2925 tsCH3(99)2907 38.45 44.92 2898 40.12 44.92 – 2902 tsCH2(99)2879 27.39 78.30 2874 26.53 72.62 2878 2873 tsCH2(99)1765 589.24 14.80 1745 571.89 15.23 – 1715 tC@O(71)1745 428.15 32.30 1727 429.26 32.14 – 1715 tC@O(75)1687 11.80 16.62 1680 11.16 14.58 1685 1675 tC@C(70), dCH2(12)1608 3.38 250.94 1597 2.98 261.13 – 1599 tPh(67)1586 4.62 199.64 1574 3.08 134.64 1579 1578 tPh(59), tC@NR(22)1562 16.56 712.29 1545 15.42 764.72 1549 1552 tC@NR(63), tPh(17)1486 11.86 66.98 1485 9.95 60.45 1492 1490 dCH(19), tPh(59)1468 13.07 17.11 1473 12.37 17.63 – – dasCH3(11), dCH2(71)1456 7.06 4.93 1462 5.54 5.36 – – dasCH3(70), dCH2(17)1446 11.34 16.32 1451 9.25 17.65 – 1452 dasCH3(100)1438 37.52 18.72 1444 29.48 26.92 1443 1443 dCH2(93)1437 4.48 40.67 1436 12.18 35.45 1429 – dCH(27), tPh(47)1409 108.63 39.27 1408 3.41 26.77 – 1413 dasCH3(23), dCH2(59)1401 8.68 23.99 1397 49.44 19.53 – – dCH2(27), tCNR(45)1394 2.51 10.48 1397 42.43 36.48 – 1392 dCH2(55), tCNR(22)1378 4.23 11.51 1383 2.63 10.03 1385 – dsCH3(76), dCH2(15)1375 12.93 7.89 1376 34.01 8.20 – – dCH2(63), dNH(12)1365 43.85 15.36 1359 42.30 21.60 – 1362 dNH(45), tCNR(13)1331 5.58 8.19 1323 7.50 9.27 1324 1327 dCH2(43), tCNR(22)1321 22.10 1.79 1317 20.19 3.21 1310 1312 dCH(44), tPh(13), dCH2(17)1303 28.83 11.35 1297 13.54 5.60 1294 ‘1293 dCH(12), tPh(66)1269 106.66 77.24 1256 124.35 89.91 1262 1260 tCC(22), tCNR(44)1259 196.07 22.27 1243 136.50 7.06 – – dCH2(12), tCN(46)1239 2.05 16.37 1238 4.88 21.37 – – dCH2(85)1236 18.80 10.22 1232 79.86 16.68 1234 1233 dCH2(44), tCC(23)1186 48.24 26.98 1180 38.76 24.98 1182 – dCH2(42), tCNR(18)1173 11.58 2.97 1175 14.19 8.00 1165 1168 dCH(77), tPh(14)1148 4.80 15.93 1149 0.21 10.72 – – dCH(77), tPh(12)1147 101.45 69.70 1130 50.94 91.87 – 1129 tNNR(45), tCO(19), tCN(10)1132 275.41 33.45 1109 344.29 23.40 1108 1108 tCO(59), tCN(15)1079 12.44 1.23 1077 13.78 1.43 – 1080 dCH(45), tPh(27)1055 3.27 1.00 1059 5.98 0.97 1048 1048 dCH3(56), dCH2(25)1036 6.19 1.69 1029 6.49 0.21 – – tPh(48), dCH(19)1027 1.32 14.52 1022 2.80 14.12 1022 1021 tPh(22), dCH(42), tCO(13)1005 2.49 16.79 1002 1.01 8.77 1001 998 dCH3(38), tCC(32)

982 6.65 64.54 980 1.61 9.18 – – dCH2(60), dCH3(18)977 1.50 10.83 979 0.13 55.66 – 979 dPh(22), tCC(42)973 32.23 2.78 972 41.88 22.88 975 – dCH2(18), dPh(12), tCO(41)966 0.25 1.84 964 0.34 2.28 – 962 cCH(81), sPh(15)962 16.53 6.25 957 16.36 9.66 – – tCC(23), tCO(26), dCH2(39)946 1.33 0.54 943 1.40 0.62 940 938 cCH(92)932 11.68 4.40 924 15.32 6.85 – – tCC(29), tCO(28), dCH3(12), dCH2(18)909 3.05 2.00 909 2.73 2.08 – 906 cCH(84)892 48.39 0.17 896 43.94 0.13 900 – cC@C(97)850 4.04 4.90 844 2.84 5.11 848 850 tCC(50), dCH2(15)830 1.26 6.04 831 1.32 6.52 – 830 cCH(100)812 44.38 3.91 803 50.56 3.84 798 – tCN(26), tCNR(13), dCH2(12)775 29.33 0.78 773 24.99 0.71 – 780 cCC(29), sRing(13), sPh(11), cCH(38)737 18.16 14.99 735 7.19 7.97 751 750 sPh(20), cC@O(19), cCH(23), sRing(12)734 26.13 17.40 729 40.98 23.50 – 732 dRing(33), cC@O(18), cNH(22)719 73.43 0.39 712 72.29 0.48 – 714 cC@O(50), cNH(20), sRing(23)684 14.34 6.85 686 1.46 9.96 690 690 dCH2(82), dCH3(10)682 17.08 7.33 680 9.17 3.69 – – sPh(51), cCH(24)679 56.08 1.98 679 64.41 3.86 – – cNH(33), sPh(13), cCH(11)673 4.84 4.82 670 9.85 5.71 – 671 dPh(17), cNH(14), sPh(13), cC@O(10)643 5.43 5.60 642 4.79 5.74 – 639 dC@O(52), dCC(13)605 0.32 4.59 609 0.32 4.71 604 613 dPh(84)588 30.19 3.02 586 33.88 2.61 585 589 dCH2(29), dPh(16), dRing(10)

452 Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456

Table 1 (continued)

B3PW91/6-31G(d) (6D, 7F) B3LYP/6-31G(d) (6D, 7F) IR Raman Assignmentsa

t IRI RA t IRI RA t t –

563 27.65 5.76 563 28.03 6.46 – 568 dRing(53), dPh(11)512 5.74 1.67 513 5.00 1.58 508 516 sPh(37), cCC(35)496 16.84 2.80 496 16.79 2.84 – 488 cC@C(26), dRing(14), dCH2(19)440 20.04 2.66 438 20.51 2.92 436 440 cC@C(35), sRing(18), sPh(14), sCH3(12)413 2.86 0.82 414 2.77 0.88 – 412 cCC(18), sRing(31), sPh(14), cC@O(11)409 3.12 3.42 408 1.93 3.06 407 – cC@C(56), sPh(11)397 5.55 2.24 399 2.89 2.43 – – sPh(72)394 2.27 1.40 395 2.82 1.70 – – sPh(19), cC@C(15), dCO(12), dCC(11)384 16.55 0.48 383 18.94 0.50 – – dC@O(22), dRing(37), cCN(11)352 1.23 1.03 352 1.10 0.96 – 358 dCC(24), sRing(26), cCN(15)334 6.35 0.90 331 6.40 0.79 – 337 dCN(25), dCC(24), sPh(35)317 1.43 1.96 318 1.46 1.89 – 320 dCC(27), sPh(15), dRing(19)275 2.41 1.13 275 2.48 1.12 – 285 dRing(26), dPh(18), dCH2(22)227 1.49 1.23 229 1.52 1.36 – 226 dCH2(19), sPh(19), dCN(12)193 3.72 0.38 190 2.85 0.33 – 188 cCN(19), dCC(17), sCH3(29), sRing(11)162 ‘0.17 0.13 164 0.14 0.12 – – sCH3(88)153 0.29 2.65 152 0.30 2.86 – – cCN(20), dCH2(13), sRing(20)147 5.54 0.24 146 5.26 0.24 – 142 sRing(57), sNH(40)122 2.75 1.34 121 3.04 1.28 – – sCO(24), sCH2(18), cCN(15)

97 0.07 3.94 97 0.13 3.48 – 92 sRing(24), cCC(21), sCO(14)80 0.04 0.69 80 0.02 1.07 – – cCN(35), sRing(10), sCO(18)62 0.42 0.40 63 0.46 0.44 – – sRing(53), sCH2(14)40 0.59 2.41 40 0.58 1.99 – – sCC(37), sRing(25)30 0.08 7.81 30 0.04 8.31 – – sCC(57), sRing(17)16 0.15 5.01 17 0.40 3.55 – – sCO(31), sCH2(53)13 0.33 3.58 12 0.05 4.71 – – sCO(58), sCH2(20)

a t – stretching; d – in-plane deformation; c – out-of-plane deformation; s – torsion; Phenyl ring – Ph; triazine ring – Ring(R); as – asymmetric; s – symmetric; IRI – IRintensity; RA – Raman activity; potential energy distribution is given in brackets in the assignment column.

Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456 453

wave numbers have a weaker intensity than those absorbing atlower wave numbers. Most of the deformation bands of the CHvibrations of the phenyl rings are not pure but contain significantcontributions for other modes (Table 1). The out-of-plane cCHmodes are observed at 940 cm�1 in the IR spectrum, 962, 938,906, 830, 780 cm�1 in the Raman spectrum for Ph. The correspond-ing B3LYP values are 964, 943, 909, 831, 773 cm�1 for the phenylring. The substituent sensitive modes of the rings and other modesare also identified and assigned (Table 1). Most of the modes arenot pure but contains a significant contribution from other modes.

In order to investigate the performance of vibrational wave-numbers of the title compound, the root mean square (RMS) valuebetween the calculated and observed wavenumbers were calcu-lated. The RMS values of wavenumbers were calculated using thefollowing expression [50].

RMS ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1n� 1

Xn

itcalc

i � texpi

� �2

r

The RMS errors of the observed IR and Raman bands are foundto be 13.80 and 13.35 for B3PW91/6-31G(d)(6D, 7F) and 10.49 and9.34 for B3LYP/6-31G(d)(6D, 7F) methods, respectively. The smalldifferences between experimental and calculated vibrationalmodes are observed. This is due to the fact that experimentalresults belong to solid phase and theoretical calculations belongto gaseous phase [51].

Frontier molecular orbitals

The energies of HOMO and LUMO are negative, which indicatesthat the studied compound is stable [52]. In the title compound,the HOMO of p nature is delocalized over the CAC bonds of thephenyl ring, CAN, C@O, CAO groups and LUMO in addition to thison the NH group (Fig. S3 supporting material). Accordingly, theHOMO–LUMO transition implies an electron density transfer from

the phenyl ring to the NH group through the triazine ring. Forunderstanding various aspects of pharmacological sciences includ-ing drug design and the possible eco-toxicological characteristicsof the drug molecules, several new chemical reactivity descriptorshave been proposed. Conceptual DFT based descriptors havehelped in many ways to understand the structure of the moleculesand their reactivity by calculating the chemical potential, globalhardness and electrophilicity. Using HOMO and LUMO orbitalenergies, the ionization energy and electron affinity can beexpressed as: I = �EHOMO, A = �ELUMO, g = (�EHOMO + ELUMO)/2 andl = (EHOMO + ELUMO)/2 [53]. Parr et al. [54] proposed the global elec-trophilicity power of a ligand as x = l2/2g. This index measuresthe stabilization in energy when the system acquired an additionalelectronic charge from the environment. Electrophilicity encom-passes both the ability of an electrophile to acquire additional elec-tronic charge and the resistance of the system to exchangeelectronic charge with the environment. It contains informationabout both electron transfer (chemical potential) and stability(hardness) and is a better descriptor of global chemical reactivity.The hardness g and chemical potential l are given by the followingrelations: g = (I � A)/2 and l = �(I + A)/2, where I and A are the firstionization potential and electron affinity of the chemical species[55]. For the title compound, EHOMO = �6.40 eV, ELUMO = �2.11 eV,energy gap = 4.29 eV, Ionization potential I = 6.4 eV, electron affin-ity A = 2.11 eV, global hardness g = 2.145 eV, chemical potentiall = �4.255 eV and global electrophilicity = l2/2g = 4.22 eV. It isseen that the chemical potential of the title compound is negativeand it means that the compound is stable [52,56]. They do notdecompose spontaneously into the elements they are made upof. The hardness signifies the resistance towards the deformationof electron cloud of chemical systems under small perturbationencountered during the chemical process. The principle of hard-ness works in chemistry and physics but it is not physically obser-vable. Soft systems are large and highly polarizable, while hardsystems are relatively small and much less polarizable.

454 Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456

Natural bond orbital analysis

NBO analysis provides the most accurate possible natural Lewisstructure of wave function, because all orbital details are mathe-matically chosen to include the highest possible percentage ofthe electron density. The larger the E(2) value, the more intensiveis the interaction between electron donors and electron acceptors,i.e. the more donating tendency from electron donors to electronacceptors and the greater the extent of conjugation of the wholesystem [57]. Delocalization of electron density between occupiedLewis type (bond or lone pair) NBO orbitals and formally unoccu-pied (anti-bond or Rydberg) non-Lewis orbital correspond to a sta-bilizing donor acceptor interaction. NBO analysis has beenperformed on the molecule, re-hybridization and delocalizationof electron density within the molecule [57]. The energy of theseinteractions can be estimated by second order perturbation theoryby the equation:

Eð2Þ ¼ DEij ¼ qiðFi;jÞ2

ðEj � EiÞ

qi is the donor orbital occupancy, Ei, Ej is the diagonal elements, Fij isthe 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 intensiveinteractions are given in Table S2 (supporting material). The sec-ond-order perturbation theory analysis of Fock matrix in NBO basisshows strong intra-molecular hyper-conjugative interactions of p-electrons. The intra-molecular hyper-conjugative interactions areformed by the orbital overlap between n(O) and r�(NAC) bondorbital which results in ICT causing stabilization of the system.The strong intra-molecular hyper-conjugative interaction ofN6AC8 from O1 of n1(O1) ? r�(N6AC8) which increases ED(0.10561e) that weakens the respective bonds leading to stabiliza-tion of 28.44 kcal mol�1. The strong intra-molecular hyper-conju-gative interaction of N4AC9 from O2 of n2(O2) ? r�(N4AC9)which increases ED (0.08504e) that weakens the respective bondsleading to stabilization of 27.98 kcal mol�1. The strong intra-molecular hyper-conjugative interaction of N6AC22 from O3 ofn2(O3) ? r�(N6AC22) which increases ED (0.06251e) that weakensthe respective bonds leading to stabilization of 15.20 kcal mol�1.Another intra-molecular hyper-conjugative interactions are alsoformed by the orbital overlap between n(N) and p�(OAC) bondorbital which results in ICT causing stabilization of the system.The strong intra-molecular hyper-conjugative interaction ofO1AC8 from N4 of n1(N4) ? p�(O1AC8) which increases ED(0.36928e) that weakens the respective bonds leading to stabiliza-tion of 59.94 kcalmol�1. Hyper-conjugative interaction of O1AC8

from N6 of n1(N6) ? p�(O1AC8) which increases ED (0.36928e) thatweakens the respective bonds leading to stabilization of60.16 kcal mol�1. The increased electron density at the oxygen,nitrogen atoms leads to the elongation of respective bond lengthand a lowering of the corresponding stretching wavenumber. TheCAOAC, AC@O, C@N, NAN, NAH stretching modes can be usedas a good probe for evaluating the bonding configuration aroundthe corresponding atoms and the electronic distribution of thebenzene molecule. Hence, the title compound is stabilized by theseorbital interactions.

The NBO analysis also describes the bonding in terms of the natu-ral hybrid orbital n2(O1), which occupy a higher energy orbital(0.26635 a.u.) with considerable p-character (100.00%) and low occu-pation number (1.83547 a.u.) and the other n1(O1) occupy a lowerenergy orbital (�0.70058 a.u.) with p-character (40.11%) and highoccupation number (1.97579 a.u.). Also n2(O2), which occupy ahigher energy orbital (�0.26949 a.u.) with considerable p-character

(99.98%) and low occupation number (1.85691 a.u.) and the othern1(O2) occupy a lower energy orbital (�0.69930 a.u.) with p-charac-ter (41.10%) and high occupation number (1.97606 a.u.). n2(O3),which occupy a higher energy orbital (�0.30469 a.u.) with consider-able p-character (99.38%) and low occupation number (1.90176 a.u.)and the other n1(O3) occupy a lower energy orbital (�0.55812 a.u.)with p-character (58.29%) and high occupation number (1.96221a.u.). Thus, a very close to pure p-type lone pair orbital participatesin the electron donation to the r�(NAC) orbital for n2(O1) ? r�(-NAC), n2(O2) ? r�(NAC), n2(O3) ? r�(NAC) and p�(OAC) orbitalfor n1(N4) ? p�(OAC), n1(N6) ? p�(OAC), r�(CAC) orbital forn1(N7) ? r⁄(CAC) interactions in the compound. The results aregiven in Table S3 (supporting material).

NLO analysis

The nonlinear optical properties are associated with the delo-calized p-electrons of a molecule. The increase of the conjugationin the molecule results in a change in the NLO properties wherethe NLO properties of a molecule are related to the energy gapbetween HOMO and LUMO. The addition of substituent to conju-gated systems of organic molecules could affect the nonlinear opti-cal properties by changing the energy gap between HOMO andLUMO where the small HOMO–LUMO gap required small excita-tion energy and so the absorption bands of molecule are shiftedtoward the visible region [58,59]. The calculated first hyperpolariz-ability of the title compound is 2.82 � 10�30 esu which is compara-ble with that of similar derivatives [60,61] and is 21.69 times thatof the standard NLO material urea (0.13 � 10�30 esu) [62]. We con-clude that the title compound is an attractive object for futurestudies of nonlinear optical properties.

Molecular electrostatic potential

The molecular electrostatic potential (MEP) is a useful propertyto study the reactivity of the title compound towards electrophilicand nucleophilic attack [63–66]. The different values of the electro-static potential at the surface are represented by different colors. Inorder to predict the molecular reactive sites, the MEP for the titlecompound is calculated at B3LYP method as shown in Fig. S4(supporting material). Potential increases in the orderred < orange < yellow < green < blue where blue indicates the high-est electrostatic potential energy and red indicates the lowest elec-trostatic potential energy. Intermediary colors representintermediary electrostatic potentials. In most of MEPs, the maxi-mum negative region which is the preferred site for electrophilicattack indicated as a red color. So, an approaching electrophile willbe attracted to negative regions (mainly to points with most neg-ative values), where the electron distribution effect is dominant.From the MEP it is evident that the negative charge covers theC@O groups and the positive region is over the rings and NH group.

Geometrical parameters

The interatomic distance within the triazine ring are not equaland the CAN bond lengths are C9AN4 = 1.3945 (DFT), 1.3834(XRD), C8AN4 = 1.3865 (DFT), 1.3624 (XRD), C8AN6 = 1.3934(DFT), 1.3793 (XRD) and C10AN7 = 1.3009 (DFT), 1.2974 Å (XRD)and these values indicate that the CAN bonds show partial doublebond character in this fragment. In addition, the CAN bond lengthswere found to be much shorter than the average value for a singleCAN bond (1.47 Å), but significantly longer than a C@N doublebond (1.22 Å) [67], suggesting some multiple bond character ispresented. The CC bond lengths in the phenyl ring lie between1.3903–1.4080 (B3LYP) and 1.3784–1.40540 Å (XRD). In the titlecompound, the benzene ring is a regular hexagon with bond

Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456 455

lengths somewhere in between the normal values for a single(1.54 Å) and a double (1.33 Å) bond [68]. The C@O bond lengthsin the title compound are 1.2186, 1.2188 (B3LYP), 1.2203,1.2303 Å (XRD) and CAO bond lengths are 1.3940, 1.4246(B3LYP), 1.3933, 1.4383 Å (XRD) which are in agreements withreported values [69–71]. At C11 position of the phenyl ring, thebond angles (DFT/XRD) are, C10AC11AC12 = 122.3/123.4� andC10AC11AC20 = 118.9/117.3�, C12AC11AC20 = 118.8/119.2� and atC10 position of the triazine ring, the bond angles (DFT/XRD) areC9AC10AN7 = 120.9/120.7�, C9AC10AC11 = 121.9/122.4�, N7AC10-

AC11 = 117.2/117.0� and this asymmetry shows the interactionbetween phenyl and triazine rings. According to our calculationsat N6 position, the angle C8AN6AN7 increase by 4.8� and N7AN6-

AC22 is reduced by 5.0� from 120�, which shows the interactionbetween the triazine ring and CH2 at C22 position. The asymmetriesof the bond angles (DFT/XRD) at C28 position (C25AC28AC32

= 114.2/113.1�, C25AC28AC29 = 122.6/123.4�, C32AC28AC29 = 123.2/123.5�) reveal the steric interaction between CH2 and CH3 groupspresent in the structure. The triazine ring is tilted from the phenylring as is evident from the torsion angles C12AC11AC10AC9 = -�21.6�, C12AC11AC10AN7 = 159.4�, C20AC11AC10AC9 = 160.0� andC20AC11AC10AN7 = �19.4�. The discrepancies between the XRDresults and the calculated geometrical parameters are due to thefact that the comparison made between the experimental data,obtained from single crystal and calculated results are for isolatedmolecule in the gaseous phase.

Conclusion

The vibrational properties of 2-{[(2-Methylprop-2-en-1-yl)-oxy]methyl}-6-phenyl-2,3,4,5-tetrahydro-1,2,4-triazine-3,5-dionehave been investigated using experimental techniques (FTIR andFT-Raman) and density functional theory. The theoreticallyobtained vibrational wavenumbers were compared with theexperimental values, which yield good agreement with the calcu-lated values. The complete assignments of fundamental modeswere performed on the basis of potential energy distribution. Asit can be seen from the molecular electrostatic potential map ofthe title compound, the carbonyl groups have lowest value of elec-trostatic potential energy. In the title compound, the HOMO of pnature is delocalized over the CAC bonds of the phenyl ring,CAN, C@O, CAO groups and LUMO in addition to this on the NHgroup. The calculated first hyperpolarizability of the title com-pound is high and is an attractive object for future studies of non-linear optical properties. Quantum chemical parameters werearrived from the frontier molecular orbital theory. The calculatedgeometrical parameters are in agreement with the XRD results.

Acknowledgements

The authors would like to extend their sincere appreciation tothe Deanship of Scientific Research at King Saud University forfunding this work through the Research Group Project No. RGP-VPP-274. The authors are thankful to University of Antwerp foraccess to the university’s CalcUA Supercomputer Cluster.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2014.06.036.

References

[1] A. Nakhai, B. Stensland, P.H. Svensson, J. Bergman, Eur. J. Org. Chem. 34 (2010)6588–6599.

[2] R. Leenders, J. Heeres, D. Vandenput, R. Zijlmans, J. Guillemont, P. Lewi, Eur. J.Org. Chem. 15 (2010) 2852–2854.

[3] N. Sirisoma, A. Pervin, H. Zhang, Bioorg. Med. Chem. Lett. 20 (2010) 2330–2334.

[4] D.J. Newmann, G.M. Cragg, J. Nat. Prod. 67 (2004) 1216–1238.[5] S. Roje, Photochemistry 68 (2007) 1904–1921.[6] K.S. Jain, T.S. Chitre, P.B. Miniyar, M.K. Kathiravan, V.S. Bendre, V.S. Veer, S.R.

Shahane, C.J. Shishoo, Curr. Sci. 90 (2006) 793–803.[7] R.A. Stavenger, Annu. Rep. Med. Chem. 43 (2008) 87–102.[8] J. Depellery, R. Granet, M. Kaouadji, P. Krauz, S. Pierre, S. Delebassee, C.

Bosgiraud, Nucleosides Nucleotides 15 (1996) 995–1008.[9] M.Z. Luo, M.C. Liu, D.E. Mozdziesz, T.S. Lin, G.E. Dutschman, E.A. Gullen, Y.C.

Cheng, A.C. Sartorelli, Bioorg. Med. Chem. Lett. 10 (2000) 2145–2148.[10] H.L. Maslen, D. Hughes, M. Hursthouse, E. De Clerq, J. Balzarini, C. Simons, J.

Med. Chem. 47 (2004) 5482–5491.[11] W. Lv, B. Banerjee, K.L. Molland, M.N. Seleem, A. Ghafoor, M.I. Hamed, B. Wan,

S.G. Franzblau, A.D. Mesecar, M. Cushman, Bioorg. Med. Chem. 22 (2014) 406–418.

[12] D. Kahne, R. Kerns, S. Fukuzawa, M. Ge, C. Thompson, PCT Int. Appl. WO2000004044, 2000.;D. Kahne, R. Kerns, S. Fukuzawa, M. Ge, C. Thompson, Chem. Abstr. 132 (2000)122934.

[13] N.R. El-Brollosy, Phosphor. Sulfur Silicon 163 (2000) 77–89.[14] N.R. El-Brollosy, Monatsh. Chem. 139 (2008) 1483–1490.[15] W. Thorwart, U. Gebert, R. Schleyerbach, R.R. Bartlett, Eur. Pat. 276805, 1988.;

W. Thorwart, U. Gebert, R. Schleyerbach, R.R. Bartlett, Chem. Abstr. 110 (1989)75574.

[16] C. Subramanyam, A.J. Duplantier, M.A. Dombroski, S.-P. Chang, C.A. Gabel, C.Whitney-Pickett, D.G. Perregaux, J.M. Labasi, K. Yoon, R.M. Shepard, M. Fisher,Bioorg. Med. Chem. Lett. 21 (2011) 5475–5479.

[17] L.C. March, G.S. Bajwa, J. Lee, K. Wasti, M.M. Joullie, J. Med. Chem. 19 (1976)845–848.

[18] H. Fischer, H. Moeller, M. Budnowski, G. Atassi, P. Dumont, J. Venditti, O.C.Yoder, K.G. Henkel, Arzneim.-Forsch. 34 (1984) 663–668.

[19] M. Mansour, M.M. Eid, N.S. Khalil, Nucleosides Nucleotides 22 (2003) 21–44.[20] F. Krauth, H.-M. Dahse, H.-H. Rüttinger, P. Frohberg, Bioorg. Med. Chem. 18

(2010) 1816–1821.[21] K. Wittine, M.S. Babic, M. Košutic, M. Cetina, K. Rissanen, S.K. Pavelic, A.T.

Paravic, M. Sedic, K. Pavelic, M. Mintas, Eur. J. Med. Chem. 46 (2011) 2770–2785.

[22] K. Hirai, H. Sugimoto, T. Mizushima, Jap. Pat. 61134389, 1986.;K. Hirai, H. Sugimoto, T. Mizushima, Chem. Abstr. 106 (1987) 67353.

[23] S. Yurdakul, S. Tanribuyurdu, J. Mol. Struct. 1052 (2013) 57–66.[24] N.R. El-Brollosy, A.A. El-Emam, A.A. Al-Turkistani, S.W. Ng, Acta Cryst. E68

(2012). o347-o347.[25] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,

G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonneberg, M. Hada,M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, J.E. Peralta, F. Ogliaro, M.Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R.Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Knox, J.B. Cross, V.Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G.Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O.Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian09, RevisionB.01, Gaussian Inc., Wallingford, CT, 2010.

[26] J.B. Foresman, in: E. Frisch (Ed.), Exploring Chemistry with Electronic Structuremethods: A Guide to Using Gaussian, Pittsburg, PA, 1996.

[27] R. Dennington, T. Keith, J. Millam, GaussView, Version 5, Semichem Inc.,Shawnee Mission KS, 2009.

[28] J.M.L. Martin, C. Van Alsenoy, GAR2PED, A Program to Obtain a PotentialEnergy Distribution from a Gaussian Archive Record, University of Antwerp,Belgium, 2007.

[29] M. Belletete, J.F. Morin, M. Leclerc, G. Durocher, J. Phys. Chem. 109A (2005)6953.

[30] D. Zhenminga, S. Hepinga, L. Yufanga, L. Dianshenga, L. Bob, Spectrochim. ActaA 78 (2011) 1143–1148.

[31] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO version 3.1,Theoretical Chemistry Institute and Department of Chemistry, University ofWisconsin, Madison, 1998.

[32] C. Andraud, T. Brotin, C. Garcia, F. Pelle, P. Goldner, B. Bigot, A. Collet, J. Am.Chem. Soc. 116 (1994) 2094–2102.

[33] V.M. Geskin, C. Lambert, J.L. Bredas, J. Am. Chem. Soc. 125 (2003) 15651–15658.

[34] D.A. Kelinman, Phys. Rev. 126 (1977) 1962–1979.[35] N.B. Colthup, L.H. Daly, S.E. Wiberly, Introduction to IR and Raman

spectroscopy, Academic Press, New York, 1990.[36] N.P.G. Roeges, A Guide to the Complete Interpretation of IR Spectra of Organic

Compounds, Wiley, New York, 1994.[37] G. Socrates, Infrared Characteristic Group Frequencies, John Wiley and Sons,

New York, 1981.[38] R.M. Silverstein, G.C. Bassler, T.C. Morril, Spectrometric Identification of

Organic Compounds, fifth ed., John Wiley and Sons, Inc., Singapore, 1991.[39] K. Nakanishi, Infrared Absorption Spectroscopy Practical, Holden-Day, San

Francisco, 1962.

456 Y.S. Mary et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 449–456

[40] J.B. Bhagyasree, H.T. Varghese, C.Y. Panicker, J. Samuel, C. Van Alsenoy, K.Bolelli, I. Yildiz, E. Aki, Spectrochim. Acta A 102 (2013) 99–113.

[41] L.J. Bellamy, The IR Spectra of Complex Molecules, John Wiley and Sons, NewYork, 1975.

[42] A. Spire, M. Barthes, H. Kallouai, G. De Nunzio, Physics D 137 (2000) 392–396.[43] R. Minitha, Y.S. Mary, H.T. Varghese, C.Y. Panicker, R. Ravindran, K. Raju, V.M.

Nair, J. Mol. Struct. 985 (2011) 316–322.[44] C.Y. Panicker, H.T. Varghese, V.S. Madhavan, S. Mathew, J. Vinsova, C.V.

Alsenoy, Y.S. Mary, Y.S. Mary, J. Raman Spectrosc. 40 (2009) 2176–2186.[45] S. Kundoo, A.N. Banerjee, P. Saha, K.K. Chattophyay, Mater. Lett. 57 (2003)

2193–2197.[46] S. Genc, N. Dege, A. Cetin, A. Cansiz, M. Sekerci, M. Dincer, Acta Cryst. E60

(2004) o1580–o1582.[47] H. Tanak, Y. Koysal, Y. Onver, M. Yavuz, S. Isik, K. Sancak, Mol. Phys. 108 (2010)

127–139.[48] G.L. Almajan, S.F. Barbuceanu, L. Farcasanau, C. Draghici, Rev. Chim. 62 (2011)

386–390.[49] J. Coates, in: R.A. Meyers (Ed.), Encyclopedia of Analytical Chemistry:

Interpretation of Infrared Spectra. A Practical Approach, John Wiley and SonsLtd., Chichester, 2000.

[50] T. Joseph, H.T. Varaghese, C.Y. Panicker, T. Thiemann, K. Viswanthan, C. VanAlsenoy, T.K. Manojkumar, Spectrochim. Acta A 117 (2014) 413–421.

[51] Y.S. Mary, K. Raju, T.E. Bolelli, I. Yildiz, H.I.S. Nogueira, C.M. Granadeiro, C. VanAlsenoy, J. Mol. Struct. 1012 (2012) 22–30.

[52] R. Parthasarathi, V. Subramanian, D.R. Roy, P.K. Chattaraj, Bioorg. Med. Chem.12 (2004) 5533–5543.

[53] T.A. Koopmans, Physica 1 (1993) 104–113.[54] R.J. Parr, L.V. Szentpaly, S. Liu, J. Am. Chem. Soc. 121 (1999) 1922–1924.[55] R.J. Parr, R.G. Pearson, J. Am. Chem. Soc. 105 (1983) 7512–7516.[56] B. Kosar, C. Albayrak, Spectrochim. Acta 87 (2011) 160–167.[57] S. Sebastian, N. Sundaraganesan, Spectrochim. Acta A 75 (2010) 941–952.[58] K.S. Thanthiriwatte, K.M.N. de Silva, J. Mol. Struct. Theochem. 617 (2002) 169–

175.[59] R.G. Pearson, Proc. Natl. Acad. Sci. 83 (1986) 8440–8441.[60] S. Muthu, A. Prabakaran, Spectrochim. Acta A 121 (2014) 420–429.[61] V. Sangeetha, M. Govindarajan, N. Kanagathara, M.K. Marchewka, S.

Gunasekaran, G. Anbalagan, Spectrochim. Acta A 118 (2014) 1025–1037.[62] M. Adant, L. Dupuis, L. Bredas, Int. J. Quantum. Chem. 56 (2004) 497–507.[63] A. Tokatli, E. Özen, F. Ucun, S. Bahçeli, Spectrochim. Acta A 78 (2011) 1201–

1211.[64] E. Scrocco, J. Tomasi, Adv. Quantum Chem. 11 (1978) 115–193.[65] F.J. Luque, J.M. Lopez, M. Orozco, Theoret. Chem. Acc. 103 (2001) 343–345.[66] N. Okulik, A.H. Jubert, Int. Electron J. Mol. Des. 4 (2005) 17–30.[67] A.F. Holleman, E. Wiberg, N. Wiberg, in: De Gruyter (Ed.), Lehrburch der

Anorganischen Chemie, Berlin, New York, 2007.[68] Y.S. Mary, K. Raju, I. Yildiz, O. Temiz-Arpaci, H.I.S. Nogueira, C.M. Granadeiro, C.

Van Alsenoy, Spectrochim. Acta A 96 (2012) 617–625.[69] I. Sidir, Y.G. Sidir, E. Tasal, C. Ogretir, J. Mol. Struct. 980 (2010) 23–244.[70] E. Inkaya, M. Dincer, E. Korkusuz, I. Yildirim, J. Mol. Struct. 2013 (2012)

67–74.[71] T. Rajamani, S. Muthu, Solid State Sci. 16 (2013) 90–101.