Molecular structure, vibrational, electronic and ...

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 340–352

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Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations P.B. Nagabalasubramanian a,⇑, S. Periandy b, Mehmet Karabacak c, M. Govindarajan d a

Department of Physics, Arignar Anna Govt. Arts & Science College, Karaikal, Puducherry, India Department of Physics, Tagore Arts College, Puducherry, India c Department of Mechatronics Engineering, H.F.T. Technology Faculty, Celal Bayar University, Turgutlu, Manisa, Turkey d Department of Physics, Avvaiyar Govt. College for Women, Karaikal, Puducherry, India b

h i g h l i g h t s

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

Spectroscopic features of 4-VCH were

examined my FT-IR and FT-Raman. Frontier molecular orbital, global

reactivity descriptors and electronic transitions were analyzed. Stability, charge delocalization were analyzed using NBO theory. Comparison of atomic charges by Mulliken and NBO analyses were predicted. Electrostatic potential, total density and molecular electrostatic potential were investigated.

a r t i c l e

i n f o

Article history: Received 5 September 2014 Received in revised form 27 February 2015 Accepted 2 March 2015 Available online 9 March 2015 Keywords: 4-Vinylcyclohexene Vibrational analysis DFT NLO and NBO HOMO–LUMO

a b s t r a c t The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000–100 cm1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV–Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. Ó 2015 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 9443875224. E-mail address: [email protected] (P.B. Nagabalasubramanian). http://dx.doi.org/10.1016/j.saa.2015.03.043 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

P.B. Nagabalasubramanian et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 340–352

Introduction In the case of 4-VCH, vinyl double bonds were reported to take part in the polymerization reaction, as the endocyclic double bond shows little ring strain and large steric hindrance. In the literature [1], half-chair conformation for cyclohexene was proposed on the basis of its measurements of the heats of bromination of cyclic olefins. Later in literature [2], the energy for different conformations was investigated and predicted that the most stable conformation was indeed the half-chair form (C2 symmetry). Subsequently other theoretical calculations on the conformation of cyclohexene were published [3–5]. The half-chair conformation of cyclohexene was indicated by infrared and Raman spectra [6]. There are earlier literatures in Raman spectrum of 4,5-dichlorocyclohexene [7,8], X-ray diffraction studies of pentachlorocyclohexene [9,10] and electron diffraction results for 3,4,5,6-tetra-chlorocyclohexene [11]. A half-chair conformation is also present in cyclohexene oxide [12,13]. The FT-IR and FT-Raman vibrational analysis of 4-VCH [14] and the electronic spectra of 1-VCH [15] were studied. The earlier literatures indicates that neither quantum chemical calculations nor the electronic properties and thermal properties of 4-vinylcyclohexene have been reported up to now in the detailed manner. Since there has been no exhaustive determination of the molecular structure of 4-VCH, this investigation was deemed necessary. The scantiness observed in the literature encouraged to do this theoretical and experimental vibrational spectroscopic research to provide a correct assignment of the fundamental bands in experimental FT-IR and FT-Raman spectra on the basis of the calculated TED. The present study intends to give a complete description of the molecular geometry, molecular vibrations, electronic properties (UV–Vis, FMO, MEP, NBO, atomic charges and global reactivity descriptors) and thermodynamic properties. A correlation graph was drawn between standard heat capacities (C), standard entropies (S), and standard enthalpy changes (H) with various temperatures. Experimental details The compound under investigation namely 4-VCHwas purchased from Aldrich Chemicals, USA which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FT-IR spectra of the title compound were recorded in Brunker IFS 66V Spectrometer in the range of 3600–10 cm1. The spectral resolution is ±2 cm1. The FT-Raman spectra of compound was also recorded in the same instrument with FRA 106 Raman module equipped with Nd:YAG laser source operating at 1.064 lm line width with 200 mW power. The spectra were recorded with scanning speed of 30 cm1 min1 of spectral width 2 cm1. The frequencies of all sharp bands are accurate to ±1 cm1. Computational methods The primary task for the computational work is to determine the optimized geometry of the compound. The molecular structure optimization of the title compound and corresponding vibrational harmonic frequencies are calculated using DFT with hybrid Beckee-3-Lee-Yag-Parr(B3LYP) combined with 6-311++G(d,p) basis set using GAUSSIAN09package program without any constraint on the geometry. The stability of the optimized geometries is confirmed by wavenumber calculations, which gave positive values for all the obtained wavenumbers. TED calculations are carried out by VEDA4 program [16] which show the relative contributions of the redundant internal coordinates to each normal vibrational mode of the molecule and thus enable us numerically to describe

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the character of each mode. The optimized geometrical parameters, true rotational constants, fundamental vibrational frequencies, IR and Raman intensities, atomic charges, dipole moment, and other thermodynamical parameters were calculated using the Gaussian09 package [17]. By combining the results of the GAUSSVIEW [18] program with symmetry considerations, vibrational frequency assignments were made with a high degree of accuracy. To make best fit with the experimental frequencies, theoretical frequencies greater than 1700 cm1 were scaled with 0.958 [19] and less than 1700 cm1 were scaled with 0.9614 [19]. UV–Visible study was performed using TD-DFT [20–23] with B3LYP/6-311++G(d,p) basis set, based on the optimized structure in solvent (ethanol, DMSO and water) and gas phase to predict the electronic properties viz., HOMO–LUMO energies, dipole moment, absorption wavelengths, and oscillator strengths etc. The molecular electrostatic potential surface (MEPs) of the present molecule is illustrated and evaluated. The global reactivity descriptors like chemical potential, electronegativity, chemical hardness, softness and electrophilicity index can be calculated using DFT. The electronic chemical potential, describing the escaping tendency of electron from a stable system can be calculated as l = (IP + EA)/2. Electronegativity (v) is described as negative of the electronic chemical potential. Chemical hardness which demonstrates the resistance to alteration in electron distribution is given by g = (IP EA)/2, and is well correlated with the stability and reactivity of the chemical system. The inverse of the hardness is expressed as the global softness f = (1/g). The global electrophilicity index (w), introduced is calculated in terms of chemical potential and the hardness as w = l2/2g and assess the lowering of energy due to maximal electron flow between donor and acceptor. Here the ionization potential(IP) and electron affinity (EA) are defined as the difference in ground state energy between the cationic and neutral system and difference in ground state energy between neutral and anionic system i.e., IP = E(N 1)–E(N) = EHOMO and EA = E(N) E(N + 1) = ELUMO. The changes in the heat capacity, entropy, and enthalpy of the title molecule were investigated for the different temperatures (from 100 K to 700 K) from the vibrational frequencies.

Results and discussion Geometrical structure The molecular structure along with numbering of atoms of 4-VCH is obtained from Gaussian09 program and is as shown in Fig. 1. The global minimum energy obtained by DFT structure optimization using 6-311++G(d,p) basis set for the title molecule as 312.12754 a.u. The most optimized structural parameters (bond length, bond angle and dihedral angle) calculated by the same method are compared with the microwave and electron diffraction experimental data and represented in Table 1 in accordance with the atom numbering scheme given in Fig. 1. The moment of inertia of the molecule varies as IA > IB > IC and the rotational constants as 4.25340, 1.37225 and 1.12508 GHz respectively indicates that the molecule is an asymmetric top molecule. In this paper, the bond length and bond angles obtained theoretically were compared with the molecular structure of cyclohexene [24] in the vapor phase where electron diffraction method was utilized. In the above stated literature [24], geometrical parameters were obtained by least-squares analysis of the reduced molecular intensity pattern. In this paper, the bond lengths of C1@C6 & C15@C18 (vinyl) are 1.507 Å and 1.332 Å, respectively which were 1.335 Å and 1.350 Å [15] in the earlier literature shows that the presence of vinyl group elongates the double bond in the

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results are for molecule in the solid state. The experimental value of CAH bond lengths of cyclohexene by the earlier study [15] were around at 1.093 ± .015 Å while of theoretical values it ranges between 1.0844 to 1.0972 Å in this study. This larger deviation of CAH bond lengths may be due to the low scattering factors of hydrogen atoms in electron diffraction experiments which are not included in the theoretical calculations. The presence of vinyl group in the 4th carbon atom elongates the bond lengths of C3AC4, C4AC5 approximately by 0.03–0.4 Å greater than the other bonds in the ring. The C4AC15, i.e., CringACvinyl, bond length calculated by B3LYP/ 6-311++G(d,p) is 1.503 Å which is 0.04 Å greater than the value reported in literature [15] shows that position of substitution also changes the bond length value. The bond angles C4AC15AC18 is 125.54°, C3AC4AC15 is 111.73° and C5AC4AC15 is 111.29° which deviated from the normal value of 120° shows that the ring is distorted due to the substitution. Vibrational assignments

Fig. 1. The theoretically optimized geometric structure of 4-VCH at DFT-B3LYP/6311++G(d,p) level of theory.

ring due to substitutional effect. Also, the bond length obtained between C15@C18 in this paper varies slightly with the value reported in the earlier literature [15] by 0.02 Å. The CAC bonds in the ring are not of the same length such that the bonds C1AC2, C2AC3, C3AC4, C4AC5, and C5AC6 are 1.507, 1.535, 1.543, 1.544 and 1.508 Å, respectively. From the theoretical values, one can find that most of the optimized bond lengths are larger than the experimental values, as the theoretical calculations refer to isolated molecules in the gaseous phase and the experimental

The aim of this part of the study is the assignment of the vibrational absorptions to make a comparison with the related molecules and also with the results obtained from the theoreticalcalculations.4-VCHmoleculeconsists of 20 atoms with 54 normal modes of vibrations and considered under C1 point group symmetry. The detailed analysis of fundamental modes of vibration with FT-IR and FT-Raman experimental frequencies, unscaled and scaled vibrational frequencies, and TED of 4-VCHusing DFT method with 6-311++G(d,p) basis set are reported in Table 2. All vibrations are active both in IR and Raman. The experimental FT-IR and FT-Raman spectra were shown in Figs. 2 and 3, respectively. The TED for each normal mode among the symmetry coordinates of the molecule was calculated. A complete assignment of the fundamentals was proposed based on the calculated TED values, infrared and Raman intensities. Calculated Raman and IR intensities helped to distinguish and more precisely assign those fundamentals which are close in frequency. The calculated harmonic force constants and wavenumbers are usually higher than the corresponding experimental quantities because of the combination of electron correlation effects and basis set deficiencies. The observed slight disagreement between theory and experiment

Table 1 Comparison of geometric parameters (bond lengths (Å), and bond angles (°)) for 4VCH calculated by B3LYP 6-311++G(d,p) method. Parameters bond lengths (Å)

Theoretical values DFT/B3LYP 6311++G(d,p)

Expt. values

Bond angles (°)


Bond angles (°)


C1C2 C1C6 C1H7 C2C3 C2H8 C2H13 C3C4 C3H9 C3H14 C4C5 C4C15 C4H16 C5C6 C5H10 C5H12 C6H11 C15H17 C15C18 C18H19 C18H20

1.507 1.334 1.087 1.535 1.096 1.099 1.543 1.097 1.094 1.544 1.503 1.098 1.508 1.100 1.096 1.871 1.091 1.332 1.086 1.084

1.504a 1.335a

C2C1C6 C2C1H7 C6C1H7 C1C2C3 C1C2H8 C1C2H13 C3C2H8 C3C2C1 H8C2H13 C2C3C4 C2C3H9 C2C3H14 C4C3H9 C4C3H14 H9C3H14 C3C4C5 C3C4C15 C3C4H16 C5C4C15 C5C4H16

123.25 117.25 119.50 112.24 109.64 109.36 109.92 110.04 105.41 111.44 109.40 110.32 108.77 109.96 106.83 109.56 111.73 107.90 111.29 107.88

C15C4H16 C4C5C6 C4C5H10 C4C5H12 C6C5H10 C6C5H12 H10C5H12 C1C6C5 C1C6H11 C5C6H11 C4C15H17 C4C15C18 H17C15C18 C15C18H19 C15C18H20 H19C18H20

108.33 112.71 109.69 109.44 109.49 109.85 105.42 123.63 119.49 116.87 115.52 125.54 118.94 121.55 121.71 116.74

Numbering atoms ref Fig. 1. a Ref. [25]. b Ref. [15].

1.504a

1.515a

1.550a 1.468b 1.515a

1.350b


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Table 2 Experimental and calculated B3LYP level vibrational frequencies (cm1) with TED(%) of 4- Vinylcyclohexene. Sl. No.

Experimental frequency FT-IR

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

3080 3025

FT-Raman

3080 3025 3010

3000 2980 2920 2910 2895 2880 2870 2860 2850 1650 1640 1460 1450 1420 1390 1350

1250 1210 1190 1180 1140 1080 1050 1030 995 940 910 880 805 750 720 650 515 480 403 360 280 195 130

2850 1650 1640 1460 1450 1420 1390 1350 1330 1310 1295 1270 1260 1250 1210 1190

1080 1050 1030 1000 995 960 940 920 910 870 805 750 720 650 640 515 480 360 320 280

Theoretical frequency

IR intensity

b

17.62 44.46 8.873 6.58 23.11 37.05 36.41 37.98 36.41 2.88 28.31 20.78 6.49 18.65 4.15 8.71 1.20 2.68 0.54 0.49 1.40 2.20 0.93 1.07 1.16 2.59 0.59 0.77 4.41 1.51 0.53 0.50 3.7 14.0 0.19 1.63 0.32 41.19 12.81 7.63 2.19 0.66 8.72 9.15 30.62 0.64 1.50 0.48 0.40 0.51 0.27 0.26 0.12 0.02

masym C18H20 (99) msym C1H7 (99) masym C6H11 (99) msym C18H19 (94) masym C15H17 ((93) masym C3H14 (96) masym C5H12 (86) masym C2H8 (87) msym C3H9 (93) msym C4H16 (88) msym C2H13 (92) msym C5H10 (91) mC1@C6 (76) mC15@C18 (70)+ b CH (12)

Vibrational assignments and TED%

B3LYP 6311++ G(d,p) Unsclaed

Scaleda

3206 3151 3128 3124 3104 3063 3037 3032 3014 3002 2989 2983 1710 1697 1497 1480 1476 1456 1416 1386 1368 1361 1329 1322 1304 1277 1247 1210 1165 1150 1085 1079 1051 1030 1000 984 959 945 932 922 873 816 740 678 663 522 485 516 387 324 276 188 114 86

3071 3019 2997 2993 2974 2934 2909 2905 2887 2876 2863 2858 1644 1631 1439 1423 1419 1400 1361 1333 1315 1308 1278 1271 1254 1228 1199 1163 1120 1106 1043 1037 1010 990 961 946 922 909 896 886 839 785 711 652 637 502 466 496 372 311 265 181 110 83

CH (76) CH (91) CH (91) CH2 (vinyl) (73)+ mC-C (12) CH (76) m C5-C6 (71)+ b CH (14)+ UHCCC (21) m C1-C2 (50)+ b CH (19)+UHCCC (35) b CH (41)+ UHCCC (25) b CH (vinyl) (32)+ m C–C (10)+UHCCC (23) b CH2 (vinyl) (26) + UHCCC (22) b CH (45)+ UHCCC (14) b CH (32)+ UHCCC (19) b CH (46)+ UHCCC (10) b CH (54)+ UHCCC (11) b CH (55) m C4–C15 (26)+ b CH (26) m C4-C3 (25)+ b CH (10) m C4–C5 (28)+ b CH(12)+ UCCCC (12) m C2-C3 (47)+ b CH (10) c CH (vinyl) [UHCCC (81)] c CH (vinyl) [UHCCC (71)+ UCCCC (10)] c CH2 (vinyl) (35) c CH (vinyl) (38) c CH2 (vinyl) [UHCCC (33)+ UCCCC (57)] c CH (vinyl) (33) c CH (vinyl) (68) Ring m C–C–C (61) Ring m C–C–C (61) ring C–C–C (TB) (66) c CH2 (vinyl) [UHCCC (37)+ UCCCC (19)] c CH (vinyl) [UHCCC (27)+ UCCCC (25)] Ring C–C–C (TB) (60) Ring C–C–C (TB) (58) Ring C–C–C (IPB) (40) Ring C–C–C (IPB) (25) c CH [UHCCC (48)+ UCCCC (22)] c CH (vinyl) (73) c ring (73) c ring (73) c CH2 (vinyl) (77) b b b b b

Numbering of atoms, ref Fig. 1. a Wavenumbers ranges from 4000 to 1700 cm1 and lower than 1700 cm1 are scaled with 0.958 and 0.9614 for B3LYP/6-311++G(d,p) basis set, respectively. b TED: Total energy distribution m; stretching, b,IPB; in-plane bending, c; out-of-plane bending, TB; triangular bending, U-Torsion.

could be a consequence of the anharmonicity and the general tendency of the quantum mechanical methods to overestimate the force constants at the exact equilibrium geometry. To improve the calculated values in agreement with the experimental values, proper scaling factors were utilized. CAH vibrations The hetero aromatic structure shows the presence of CAH stretching vibrations in the region 3000–3100 cm1 which is the characteristic region for ready identification of CAH stretching

vibration [25]. But in cyclohexene, most of the CAH stretching absorptions are usually observed below 3000 cm1 [14]. For present molecule, there 12 stretching vibrations for CAH modes out of which 9 vibrations belong to ring CAH modes and other 3 vibrations for vinyl group CAH modes. Since there are two hydrogen atoms connected with each carbon atom in the ring except double bond carbon and the vinyl group substituted carbon (4th position), the vibrations occurred one as symmetric CAH stretching and another as CAH asymmetric stretching, explained in Table 2. The symmetric CAH modes are assigned to the wavenumbers 2880,

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Fig. 2. Experimental FT-IR spectrum of 4-VCH.

Fig. 3. Experimental FT-Raman spectrum of 4-VCH.

2870 cm1 (FT-Raman), and 3000, 2860 cm1 (FT-IR) and 3025, 2850 cm1 (both), whereas the asymmetric CAH modes are observed at 3010, 2980, 2910 cm1 (FT-Raman), and at 2920, 2895 cm1 (FT-IR), and at 3080 cm1 (both). The detailed contribution of atoms for these stretching vibrations is given in Table 2. As expected, all the stretching modes are pure stretching modes as are evident from the TED column in Table 2; they almost contribute around 100%. The bands due to CAH in-plane ring vibration interacting with CAC stretching vibrations and are observed as a number of m–w intensity sharp bands in the region 1000–1300 cm1 which reflects the characteristics of the molecule [25]. For the present molecule, the both in-plane and out-of plane CAH bending vibrations observed in the regions are mentioned in Table 2 and predicted values are coinciding very well with the observed frequencies calculated in DFT. In connection with earlier literatures, here, the CAH in-plane bending vibrations observed at 1460, 1450, 1420, 1250, 1210, and 1190 cm1 in both the spectra and 1180, 1140 cm1 in FT-IR are referred as scissoring vibrations but the vibration at 1350 cm1 (both) is observed as rocking vibration. Also, the peak occurred at 1295 cm1 of FT-Raman is assigned to CAH in-plane-bending vibration. The aromativity of the compound obviously proved by the presence of the strong peak below 900 cm1 and the substitution patterns on the ring can be judged from the out of plane bending of the ring CAH bond in the range of 900–675 cm1 which are more informative [26]. Besides, the CAH out-of-plane bending vibrations are strongly coupled vibrations and occur in the region 900– 667 cm1 [27]. In the present study, the peaks at 960, 920, 870, and 640 cm1 (FT-Raman), and 880 cm1 (FT-IR), and 650 cm1 (both) confirm the CAH out of plane bending vibrations which agree well with the above said literature values. Since these CAH vibrations are mixed vibrations, some of the vibrations are below

the above said literature values and TED values for these CAH out-of-plane vibrations are shown in Table 2. C@C and CAC vibrations The ring stretching vibrations are important and highly characteristic of the aromatic ring itself. Mono substituted alkyl molecule, the C@C stretching vibrations occur in the region 1670–1640 cm1 [28]. In the literature [29], it is mentioned that the presence of conjugate substituted such as C@C causes a heavy doublet formation around at 1650 cm1. As predicted in literatures [28,29], the strong doublet formation of C@C aromatic stretch is observed at 1650 and 1640 cm1 in both the spectra are due to C@C stretching vibration of the ring and the vinyl group respectively. In this molecule, there are five CAC stretching vibrations which are mixed vibrations with in-plane-bending modes. The CAC stretching vibrations are assigned to the peaks at 1330, 1310, 1000 cm1 (FT-Raman), and at 1080, 1050, 1030 cm1 (both), and the contribution of atoms for this CAC stretching modes are shown in the TED column of Table 2. Vinyl group (CH@CH2) vibrations Basically, mono substituted alkyl group (vinyl group) has two CAH stretching vibrations in the range 3010–3040 cm-1 and 3075–3095 cm1 in which both has medium intensity peaks. Also, as in literature [28], the CAH vibrations of C@CH2 of vinyl group occurs at 3080, 2975 cm1 and for C@CH, it is at 3020 cm1. In line with the above literature values, here, CAH symmetric and asymmetric vibrations of vinyl group (C@CH2) are assigned at 3000 cm1 (FT-IR), 3080 cm1 (both) respectively. The asymmetric CAH stretching vibration of C@CH of vinyl group is assigned at 2980 cm1 of FT-Raman which is 40 units less than the predicted value is due to the dominant vibration of the ring HAC@CAH.

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The peak at 1390 cm1 appeared in both spectra is assigned to CH2 scissoring in-plane vibration while the peaks at 1270, 1260 cm1of FT-Raman are assigned to CH2 twisting vibrations which are coincidence with the literature values [28] which predicts that CH2 twisting will observe in the region 1350– 1150 cm1 which are weaker than those resulting from CH2 scissoring. The peaks at 940, 650 cm1 appeared in both the spectra are assigned to out of plane vibrations (twisting) of vinyl C@CH2 group while at 910 cm1 (both) and the theoretical value at 86 cm1 are assigned to wagging vibrations. Moreover, the peaks at 995 cm1 (both) and 280 cm1 (both) assigned to wagging and twisting vibrations respectively of vinyl C@CH group. These out-of-plane vibrations are mixed vibrations as it clear from the TED column of Table 2. Ring vibrations The ring vibrations include of CACAC ring breathing, trigonal bending, in-plane and out-of-plane bending vibrations. The peaks appeared in both spectra at 805, 750, 720, 515, 480, 360 cm1 and 403, 195, 130 cm1 of FT-IR are assigned to ring vibrations. These vibrations are mixed vibrations as evident from the TED column in Table 2. Electronic properties Frontier molecular orbital analysis The frontier molecular orbitals, HOMO and LUMO and frontier orbital gap helps to exemplify the chemical reactivity and kinetic stability of the molecules which are the important parameters for quantum chemistry. The energy of HOMO is directly related to the ionization potential, while LUMO energy related to electron affinity [29]. This is also used by the frontier electron density for predicting the most reactive position in p-electron systems and also explains several types of reaction in conjugated system [30,31]. The optimization was done in order to calculate the energetic behavior and dipole moment of the title compound in gas phase and solvents (ethanol, DMSO and water). The total energy for different orbital transitions, energy gap between HOMO and LUMO, electro-negativity, chemical hardness, softness, electrophilicity index and dipole moment have been calculated with B3LYP/ 6-311++G(d,p) level. Results obtained from solvent and gas phase are listed in Table 3. The energy values of HOMO are computed as 6.7134, 6.7568, 6.7622, 6.7622 eV and LUMO as 0.2332, 0.1925, 0.1925, 0.1898 eV, and the energy gap values are 6.4802, 6.5643, 6.5697, 6.5724 eV in gas, ethanol, DMSO and water phase for 4VCH molecule, respectively. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. Surfaces for the frontier orbitals were drawn to understand the bonding scheme of present compound. The four important molecular orbitals (MO) for the title molecule: the second highest and highest occupied MOs and the lowest and the second lowest unoccupied MOs which were denoted as HOMO1, HOMO, LUMO and LUMO+1, respectively are the critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. The surfaces of FMOs (HOMO1, HOMO, LUMO and LUMO+1) are drawn and given in Fig. 4 to understand the bonding scheme of present compound. The positive phase is red and the negative one is green. From Fig. 4 it is evident that the HOMO of 4-VCH submits a charge density localized at C@C bonds on the ring, but LUMO is characterized by a charge distribution at CAH bonds on the ring. Dipole moment reflects the molecular charge distribution and is given as a vector in three dimensions. Therefore, it can be used as illustrator to depict the charge movement across the molecule. The

Table 3 Calculated energy values of 4-VCH in gas phase, ethanol, DMSO and water. TD-DFT/B3LYP/6311++G(d,p)

Gas

Ethanol

DMSO

Water

Etotal (Hartree) EHOMO (eV) ELUMO (eV) DEHOMO–LUMO gap (eV) EHOMO1 (eV) ELUMO+1 (eV) DEHOMO1LUMO+1 gap (eV) Ionization potential (eV) Electron affinity (eV) Electronegativity v (eV) Chemical hardness g (eV) Softness f (eV)1 Electrophilicity index (w) Dipole moment (Debye)

312.1275 6.7134 0.2332 6.4802 7.1174 0.0407 7.0767

312.1296 6.7568 0.1925 6.5643 7.1852 0.0949 7.0903

312.1297 6.7622 0.1925 6.5697 7.1879 0.0976 7.0903

312.1297 6.7622 0.1898 6.5724 7.1879 0.1003 7.0876

6.7134

6.7568

6.7622

6.7622

0.2332 3.4733

0.1925 3.4747

0.1925 3.4774

0.1898 3.4760

3.2401

3.2821

3.2848

3.2862

1.6201 0.1543

1.6411 0.1523

1.6424 0.1522

1.6431 0.1522

0.2582

0.3580

0.3620

0.3639

direction of the dipole moment vector in a molecule depends on the centre’s of negative and positive charges. Dipole moments are strictly identified for neutral molecules. For charged systems, its value depends on the choice of origin and molecular orientation. Table 3 depicts that the molecule at gas phase has lesser dipole moment (0.2582 D) than others. The dipole moment of the studied molecule in water is greater than DMSO and ethanol. It varies as water (0.3639) > DMSO (0.3620) > ethanol (0.3580). Also, it is clear that in going from the gas phase to the solvent phase, the dipole moment value increases. Global reactivity descriptors The calculated values of these global reactivity descriptors for the title molecule are collected in Table 3. The value of chemical hardness is 3.2401 eV (gas phase). Considering the chemical hardness, a molecule is hard if it has large HOMO–LUMO gap and it is soft if it has small gap. One can also relate the stability of molecule to hardness by means that the molecule with least HOMO–LUMO gap is more reactive. UV–Visible spectra analysis Molecules allow strong p–p⁄ and r–r⁄ transition in the UV– Visible region with high extinction coefficients [32]. We have performed this optimization in order to investigate the energetic behavior and dipole moment of the 4-VCH theoretically. To analyze the electronic transitions of the title compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (ethanol, DMSO and water) were performed. The calculated frontier orbital energies, absorption wavelengths (k), oscillator strengths (f) and excitation energies (E) for gas phase and solvents are illustrated in Table 4. The visible absorption maxima of this molecule from calculations of the molecular orbital geometry show that correspond to the electron transition between frontier orbitals such as translation from HOMO to LUMO. According to Frank– Condon principle, the maximum absorption peak (kmax) in UV– Visible spectrum corresponds to vertical excitation. TD-DFT calculations predict six transitions in the UV region for 4-VCH. As can be seen from Table 4, the calculated absorption maxima for HOMO to LUMO transition is 217.3, 214.7, 214.6 and 214.5 nm for gas, ethanol, DMSO and water respectively at DFT/B3LYP/6311++G(d,p) method. As can be seen, all calculations performed are very close. In view of the calculated absorption spectra, the

346


Fig. 4. Frontier molecular orbital energy level diagram of 4-VCH.

Table 4 Calculated wavelengths k (nm), excitation energies (eV), oscillator strengths (f) in gas, ethanol, DMSO and water for 4-VCH. Solvent

k (nm)

E (eV)

f (a.u)

Major contribution

Gas

217.2 205.7 199.9 199.7 196.4 195.9

5.7067 6.0277 6.1994 6.2071 6.3122 6.3280

0.0072 0.0033 0.0266 0.0060 0.0070 0.0038

H?L (91%) H?L + 1 (99%) H-1?L (76%) H?L + 3 (58%) H?L + 2 (45%) H?L + 5 (60%)

Ethanol

214.7 206.0 197.3 196.4 193.9 192.9

5.7752 6.0187 6.2846 6.3144 6.3916 6.4263

0.0121 0.0038 0.0407 0.0077 0.0140 0.0077

H?L (91%) H?L + 1 (99%) H-1?L (73%) H?L + 3 (96%) H?L + 2 (74%) H?L + 5 (77%)

DMSO

214.6 206.0 197.2 196.2 193.9 192.8

5.7763 6.0182 6.2864 6.3177 6.3940 6.4294

0.0126 0.0040 0.0421 0.0080 0.0111 0.0077

H?L (91%) H?L + 1 (99%) H1?L (73%) H?L + 3 (95%) H?L + 2 (74%) H?L + 5 (77%)

Water

214.5 206.0 197.1 196.1 193.8 192.7

5.7802 6.0183 6.2904 6.3209 6.3964 6.4321

0.0121 0.0037 0.0405 0.0076 0.0099 0.0071

H?L (91%) H?L + 1 (99%) H1?L (723%) H?L + 3 (96%) H?L + 2 (74%) H?L + 5 (77%)

H: HOMO; L: LUMO.

maximum absorption wavelength corresponds to the electronic transition from HOMO to LUMO+1 with 99% contribution. Also, the second one corresponds to HOMO to LUMO with 91% contribution, (H ? L) is assigned as p–p⁄ transition. The other wavelengths, excitation energies, oscillator strengths, and calculated counterparts with major contributions are also shown in Table 4.

Molecular electrostatic potential The electrostatic potential the space around a molecule by its nuclei and electrons (treated as static distributions of charge), is a very useful property to analyze and predict molecular reactive behavior. The potential has been particularly useful as an indicator of the sites or regions of a molecule to which an approaching electrophile is initially attracted, and it has also been applied successfully to the study of interactions that involve a certain optimum relative orientation of the reactants, such as between a drug and its cellular receptor [33]. 3D plot of MEP, electrostatic potential with total density of 4VCH is illustrated in Fig. 5. The MEP which is a plot of electrostatic potential mapped onto the constant electron density surface. The importance of MEP lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading (Fig. 5) and is very useful in research of molecular structure with its physicochemical property relationship [34,35]. In MEP, maximum negative region represents the site for electrophilic attack indicated by red color while the maximum positive region represents nucleophilic attack indicated in blue color. The different values of the electrostatic potential at the surface are represented by different colors. Potential increases in the order of red < orange < yellow < green < blue. The color code of these maps is in the range between 0.01841 a.u. (deepest red) to +0.01841 a.u. (deepest blue) in compound, where blue indicates the strongest attraction and red indicates the strongest repulsion. As can be seen from the MEP map of the title molecule, while regions having the strong negative potential near the H atom of the double bond of the ring whereas lesser negative values i.e., the color code extends from yellow to red near CH2 of the vinyl group. The positive potential sites are around other most of the atoms of the molecule.


347

Fig. 5. Electrostatic potential, total density, molecular electrostatic potential surface of 4-VCH.

Natural bond orbital (NBO) analysis In order to investigate the intra- and intermolecular interactions, the stabilization energies of the title compound were performed using second-order perturbation theory. For each donor NBO (i) and acceptor NBO (j), the stabilization energy E(2) associated with electron delocalization between donor and acceptor is estimated as [36,37] 2

Eð2Þ ¼ DEij ¼ qi

Fði; jÞ ej ei

where qi is the donor orbital occupancy, ei, ej are diagonal elements (orbital energies) and Fij is the off-diagonal NBO Fock matrix element. The results of second-order perturbation theory analysis of the Fock Matrix at B3LYP/6-311++G(d,p) level of theory are presented in Table 5. This analysis has been carried out to explain the charge transfer or delocalization of charge due to the intramolecular interaction

among bonds, and also provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital and the interacting stabilization energy resulting from the second-order micro disturbance theory is reported [38,39]. The larger the stabilization energy value [E(2)], the more intensive is the interaction between electron donors and electron acceptors, i.e., the more donating tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system. Delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO orbitals and formally unoccupied (antibond or Rydberg) non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor interaction. These interactions are observed as increase in electron density (ED) in CAC anti-bonding orbital that weakens the respective bonds. These intramolecular charge transfer (r ? r⁄, p ? r⁄) can induce large nonlinearity of the molecule. The strong intramolecular hyper conjugation interaction of the r

348


Table 5 Second order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra-molecular interaction of 4-VCH. Donor (i) C1–C2

C1–C6

C1–C6

C1–H7

C2–C3

C2–H8

C2–H13

C3–C4

C3–H9

C3–H14

C4–C5

C4–C15

C4–H16

C5–C6

C5–H10

C5–H12

C6–H11

Type of bond

r r r r r r r r r r p p p p r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r

Occupancy 1.98045

1.98455

1.96005

1.97711

1.98132

1.97206

1.96801

1.96996

1.97904

1.98147

1.96832

1.97383

1.96929

1.97936

1.96799

1.97299

1.97660

Acceptor (j) C1–C6 C2–C3 C2–H8 C2–H13 C3–H14 C6–H11 C1–C2 C1–H7 C5–C6 C6–H11 C2–H8 C2–H13 C5–H10 C5–H12 C1–C6 C2–C3 C5–C6 C6–H11 C1–C2 C1–H7 C3–C4 C4–C15 C1–C6 C1–C6 C3–C4 C1–C6 C1–C6 C3–H9 C2–C3 C2–H8 C4–C5 C4–C15 C5–H12 C15–C18 C15–C18 C2–H8 C2–H13 C4–H16 C1–C2 C2–H13 C4–C5 C3–C4 C3–H14 C4–C15 C5–C6 C6–H11 C15–C18 C15–C18 C2–C3 C3–C4 C4–C5 C4–H16 C5–C6 C15–C18 C18–H20 C3–H9 C5–H10 C15–H17 C1–C6 C1–H7 C4–C5 C4–C15 C5–H10 C5–H12 C1–C6 C1–C6 C4–H16 C1–C6 C1–C6 C3–C4 C1–C2 C1–C6 C1–H7 C4–C5

Type of bond ⁄

r r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ r⁄ r⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ r⁄ r⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄

Occupancy

E(2) (kJ mol1)a

E(J) E(I) (a.u)b

F(i,j)c

0.01405 0.01219 0.01446 0.01957 0.01173 0.01547 0.01884 0.01555 0.01818 0.01547 0.01446 0.01957 0.01996 0.01453 0.01405 0.01219 0.01818 0.01547 0.01884 0.01555 0.02453 0.02318 0.01405 0.06296 0.02453 0.01405 0.06296 0.01642 0.01219 0.01446 0.02232 0.02318 0.01453 0.00804 0.02587 0.01446 0.01957 0.02598 0.01884 0.01957 0.02232 0.02453 0.01173 0.02318 0.01818 0.01547 0.00804 0.02587 0.01219 0.02453 0.02232 0.02598 0.01818 0.00804 0.00835 0.01642 0.01996 0.02220 0.01405 0.01555 0.02232 0.02318 0.01996 0.01453 0.01405 0.06296 0.02598 0.01405 0.06296 0.02453 0.01884 0.01405 0.01555 0.02232

2.42 0.78 0.61 0.52 1.36 3.16 1.92 1.43 1.98 1.44 2.01 3.53 3.56 2.00 1.39 2.32 6.00 0.78 0.94 2.30 0.72 2.11 2.28 2.74 2.75 1.03 4.60 2.68 0.58 1.36 0.74 1.09 1.56 1.41 2.23 0.51 2.53 2.99 2.80 0.51 2.82 0.73 1.68 1.03 0.85 2.14 1.28 2.42 1.74 1.07 1.06 0.56 1.79 2.64 2.34 2.93 2.84 4.31 2.46 3.10 0.87 1.85 0.52 0.57 1.00 4.53 2.71 2.32 2.68 2.79 5.90 1.38 0.78 2.28

1.31 1.01 1.03 1.02 1.04 1.07 1.17 1.19 1.17 1.19 0.67 0.66 0.66 0.68 1.19 0.90 0.94 0.96 1.03 1.05 0.98 1.04 1.17 0.55 0.87 1.17 0.54 0.89 0.98 0.99 0.97 1.03 1.00 1.26 0.63 0.89 0.89 0.88 0.92 0.89 0.87 0.97 1.01 1.03 1.02 1.04 1.26 0.63 1.01 1.00 1.00 1.01 1.06 1.29 1.06 0.88 0.88 0.92 1.31 1.07 1.00 1.06 1.02 1.03 1.17 0.55 0.88 1.17 0.55 0.87 0.94 1.19 0.96 0.88

0.050 0.025 0.022 0.020 0.034 0.052 0.042 0.037 0.043 0.037 0.033 0.043 0.044 0.033 0.036 0.041 0.067 0.024 0.028 0.044 0.024 0.042 0.046 0.035 0.044 0.031 0.045 0.044 0.021 0.033 0.024 0.030 0.035 0.038 0.034 0.019 0.042 0.046 0.045 0.019 0.044 0.024 0.037 0.029 0.026 0.042 0.036 0.035 0.038 0.029 0.029 0.021 0.039 0.052 0.045 0.046 0.045 0.056 0.051 0.052 0.026 0.040 0.021 0.022 0.031 0.045 0.044 0.047 0.034 0.044 0.066 0.036 0.025 0.040

349

P.B. Nagabalasubramanian et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 340–352 Table 5 (continued) Donor (i) C15–H17

C15–C18

C15–C18 C18–H19 C18–H20

a b c

Type of bond

r r r r r r r r r p p r r r r r

Occupancy 1.97263

1.98846

1.98117 1.98354 1.98458

Acceptor (j) C4–H16 C15–C18 C18–H19 C18–H20 C3–C4 C4–C15 C15–H17 C18–H19 C18–H20 C3–C4 C4–C5 C15–H17 C15–C18 C4–C15 C15–H17 C15–C18

Type of bond ⁄

r r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄

Occupancy

E(2) (kJ mol1)a

E(J) E(I) (a.u)b

F(i,j)c

0.02598 0.00804 0.01197 0.00835 0.02453 0.02318 0.02220 0.01197 0.00835 0.02453 0.02232 0.02220 0.00804 0.02318 0.02220 0.00804

2.70 0.76 4.87 0.86 0.52 2.37 1.11 0.89 1.13 2.60 2.84 5.58 1.08 5.96 0.64 1.21

0.90 1.18 0.94 0.95 1.13 1.19 1.19 1.18 1.19 0.65 0.65 0.96 1.19 0.96 0.96 1.19

0.044 0.027 0.061 0.026 0.022 0.048 0.033 0.029 0.033 0.037 0.038 0.065 0.032 0.068 0.022 0.034

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

and p electrons of CAC and CAH to the anti CAC, CAH, bond leads to stabilization of some part of the ring which results intramolecular charge transfer (ICT) as evident from Table 5. In the ring, the occupancy of electrons between the CAC bonds i.e., (C1AC2), (C2AC3), (C3AC4), (C4AC5), (C5AC6), r(C1AC6) and p(C1AC6) are 1.98045, 1.98132, 1.96996, 1.96832, 1.97936, 1.98455, 1.96005 respectively whereas the vinyl group CAC bonds ie., C4AC15, r(C15AC18) and p(C15AC18) occupied the electrons of 1.97383, 1.98846 and 1.98117 respectively. The strong r(C1AC2) bond overlaps with r⁄ of (C1AC2), (C2AC3), (C2AH8), (C2AH13), (C3AH14) and (C6AH11) with the occupancy of 1.98045 electrons. In this overlapping r(C1AC2) bond is contributing energy of 2.42 kJ/mol with r⁄(C1AC6) while this bond contributes the energy of 3.16 kJ/mol with r⁄(C6AH11). But in the reverse trend, the strong intramolecular hyper conjugative interaction of r(C1AC6) bond contributes the energy of 1.92 kJ/mol with r⁄(C1AC2) and 1.98 kJ/mol with r⁄(C5AC6). Moreover, p(C1AC6) overlaps with r⁄(C2AH8), r⁄(C2AH13), r⁄(C5AH10) and r⁄(C5AH12). During this overlap, 3.56 kJ/mol energy was contributed with r⁄(C5AH10). In addition, it is evident from Table 5 that a maximum stabilization energy of 6.00 kJ/mol [r(C1AH7) ? r⁄(C5AC6)] and 5.96 kJ/mol [r(C18AH20) ? r⁄(C4AC15)] are observed for the title molecule. Interpretation on atomic charges The Mulliken population analysis plays an essential role on description of atomic charges, dipole moment and electronic structure. Moreover, the atomic charges on the atom have significant function in determining the biological activity, since, the activity increases with increasing charge on atom. This population analysis is based on the linear combination of atomic orbitals and the wavefunction of the molecule. The Mulliken population analysis uses the density matrix (P) and the overlap matrix (S) to build the population matrix. It gives half the electron density of the overlap matrix to each atom, regardless of properties like electro-negativity and this analysis is mainly depends upon the basis sets used. The Natural Atomic Orbitals (NAO) for an atom is the orbital which diagonalizable the density blocks. Once the NAOs are orthogonalized, the contributions from orbitals at each center can be added together to determine the atomic charge and guaranteed that the occupation number for a particular orbital will be between 0 and 2. This makes the NBO method a bit more time consuming, but more accurate as well. The comparison of total atomic charges of 4-VCH obtained by Mulliken population analysis and NBO analysis in DFT/B3LYP are listed in Table 6 and the corresponding diagram is as shown in

Fig. 6. By comparing the charges on each atom the title molecule, the charges obtained by Mulliken is greater than that obtained from NBO and some atoms are positive in Mulliken however, are negative in NBO. The charges obtained from Mulliken and NBO analyses for the ring carbons C1, C2, C3, C5 are negative but due to electron correlation effects, the NBO charges are lesser than Mulliken charges. The vinyl group carbon (C18) has more negative value (0.580) than others obtained by Mulliken analysis but it is 0.379 in NBO. The more negative charges on the atom lead to a redistribution of electron density. On the other hand, atomic charges obtained for hydrogen in both the analyses are positive; but, the charges obtained by NBO are higher than the Mulliken charges which is contrary that happened in carbon atoms. According to Mulliken analysis, the substitution of vinyl group in the ring makes C4 atom more acidic which leads to more positive on it but in NBO, it is negative. Also, the study infers that the charge obtained by Mulliken analysis for hydrogen atoms has more variation between them (ranges from 0.122 to 0.188) whereas in NBO these charges are almost identical (ranges from 0.181 to 0.210). Thermodynamic properties Several calculated thermodynamical parameters such as ZeroPoint Vibration Energies (ZPVE), entropy, S, molar capacity, C, at constant volume, rotational constants and dipole moment have been presented in Table 7. The variations in the ZPVEs seem to be insignificant. On the basis of vibrational analysis at B3LYP/6311++G(d,p) level, the standard statistical thermodynamic functions: standard heat capacity (C 0p;m ) standard entropy (S0m ), and standard enthalpy changes (DH0m ) for the title compound were obtained from the theoretical harmonic frequencies and listed in Table 8. To analyze the change of thermodynamic functions (heat capacity, entropy and enthalpy) according to varying temperature for the title molecule, the temperature was scanned from 100 K to 700 K, in steps of 50 K and the values are listed in Table 8. From this table, it can be observed that these thermodynamic functions are increasing with temperature. The correlation equations between heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic formulae and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9985, 1.0000 and 0.9999, respectively. The corresponding fitting equations are as follows and a correlation graph is shown in Fig. 7:

C 0p;m ¼ 0:1118 þ 0:1852 T 6:1815 105 T 2

ðR2 ¼ 0:9985Þ

350


Table 6 Comparison of Mulliken, and NBO atomic charges for 4-VCH performed at B3LYP method with 6-311++ G(d,p) basis set. Atom

B3LYP/6311++ G(d,p) Mulliken Atomic Charges

C1 C2 C3 C4 C5 C6 H7 H8 H9 H10 H11 H12 H13 H14 C15 H16 H17 C18 H19 H20

NBO Charges

0.261 0.494 0.375 0.297 0.833 0.154 0.169 0.157 0.132 0.146 0.188 0.153 0.151 0.167 0.264 0.147 0.160 0.580 0.122 0.135

S0m ¼ 59:5526 þ 0:1951 T 3:5714 105 T 2

0.188 0.414 0.368 0.254 0.405 0.188 0.195 0.207 0.191 0.203 0.195 0.210 0.203 0.204 0.158 0.192 0.183 0.379 0.181 0.190

ðR2 ¼ 1:0000Þ

DH0m ¼ 0:2674 þ 0:0093 T þ 6:9731 105 T 2

ðR2 ¼ 0:9999Þ

All the thermodynamic data supply helpful information for the further study on the 4-VCH. They can be used to compute the other thermodynamic energies according to the relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermo chemical field. It should be kept in mind that all thermodynamic calculations were done in gas phase and they could not be used in solution. Nonlinear optical features The components of the NLO such as dipole moment, polarizability and first order hyperpolarizability of 4-VCHmolecule were

Table 7 Theoretically computed Zero point vibrational energy (kcal mol1), rotational constants (GHz), thermal energy (kcal mol1), molar capacity at constant volume (cal mol1 K1), entropy (cal mol1 K1) and dipole moment (Debye) of 4-VCH. Parameter

B3LYP 6-311++G(d,p)

SCF (a.u) Zero point vibrational energy Rotational constants

312.12754882 111.85225 4.25340 1.37225 1.12508 116.757 30.265 86.182 0.2582

Energy Molar capacity at constant volume Entropy Dipole moment

Table 8 Thermodynamic properties at different temperatures at the B3LYP/6-311++G(d,p) level of 4-VCH. T (K)

C (cal mol1 K1)

S (cal mol1 K1)

DH (kcal mol1)

100 150 200 250 300 350 400 450 500 550 600 650 700

11.722 16.072 20.923 25.524 30.647 35.501 40.477 46.004 51.332 56.062 60.659 65.123 70.006

65.006 70.204 75.792 80.968 86.968 91.812 97.044 102.734 108.005 114.220 119.460 125.890 131.075

1.084 1.785 2.821 4.033 5.490 7.345 9.313 11.721 14.993 17.110 20.345 23.680 26.620

computed using DFT/B3LYP/6-311++G(d,p) method. The total electric dipole moment (l), the mean polarizability , and the total first order hyperpolarizability (btotal) were calculated using their x, y, and z components and collected in Table 9. The calculation of polarizability (a) and first hyperpolarizability (b) is based on the finite-field approach. In presence of an applied electric field, the energy of a system is a function of the electric field. The first hyperpolarizability is a third rank tensor that can be described

Fig. 6. (a) Comparison of Mulliken atomic charges for 4-VCH at B3LYP/6-311++G(d,p) basis set. (b) Comparison of NBO analysis for 4-VCH at B3LYP/6-311++G(d,p) basis set.


Fig. 7. Correlation graph of calculated heat capacity, entropy and change in enthalpy for the title molecule.

Table 9 The dipole moments l (D), polarizability a ( 1024 esu), average polarizability a0 ( 1024 esu), anisotropy of polarizability Da ( 1024 esu), and first hyperpolarizability b ( 1033 esu) of 4-VCH.

lx ly lz l0 axx axy ayy axz ayz azz atotal Da

0.1734 0.1823 0.0581 0.2582 17.0354 0.5676 13.5407 0.4808 0.2810 11.4757 14.0106 29.9076

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz bx by bz b

258.7362 242.0881 11.3203 366.7864 116.7762 103.5350 97.1299 176.3713 40.9419 44.1610 93.6852 567.9325 169.7451 600.1147

descriptors etc) of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvents (ethanol, DMSO and water) were performed. Furthermore, theoretical calculations gave the thermodynamic properties (heat capacity, entropy and enthalpy) for the compound. It can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 700 K due to the fact that the molecular vibrational intensities increase with temperature. The MEP and FMO study reveals that there will be charge transfer takes place within the molecule. By comparing the charges on each atom of the title molecule, the charges obtained by Mulliken is greater than that obtained from NBO and some are positive in Mulliken, however, are negative in NBO. On the other hand, the charge for hydrogen in both the analyses is positive but, the charges obtained by NBO are higher than Mulliken which is quite opposite to that happened in carbon atoms. The calculated value of b for the title compound is relatively higher than that of urea and therefore 4-VCH molecule possesses considerable NLO properties.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

by a 3 3 3 matrix. The 27 components of the matrix can be reduced to 10 components due to the Kleinman symmetry [40]. The calculated value of mean polarizability , total first order hyperpolarizability (btotal) and dipole moment (l) of 4-VCH are 14.0106 1024 esu, 600.1147 1033 esu, and 0.2582 D, respectively. Urea is one of the prototypical molecules used in the study of the NLO properties of molecular systems. Therefore it was used frequently as a threshold value for comparative purposes. The calculated value of b for the title compound is relatively higher than that of urea. Therefore 4-VCH molecule possesses considerable NLO properties.

Conclusion The equilibrium geometries of 4-VCHwas determined and compared with electron diffraction data. The experimental FT-IR and FT-Raman spectra of 4-vinylcyclohexene were recorded and the vibrational assignments are compared with the theoretically calculated wavenumbers using DFT method with 6-311++G(d,p) basis set. The difference between the corresponding wavenumbers (observed and calculated) is very small for most of the fundamentals. Therefore, the results presented in this work for the mentioned compound indicate that this level of theory is reliable for the prediction of both infrared and Raman spectra of the title compound. UV–Visible spectral analyses of the title molecule have been analyzed by theoretical calculations. In order to predict the electronic properties (HOMO–LUMO energies, global reactive

351

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