Spectroscopic [FT-IR and FT-Raman] and theoretical [UV–Visible and NMR] analysis on α-Methylstyrene by DFT calculations

Accepted Manuscript Spectroscopic [FT-IR and FT-Raman] and theoretical [UV-Visible and NMR] analysis on α-Methylstyreneby DFT calculations N. Karthikeyan, J. Joseph Prince, S. Ramalingam, S. Periandy PII: DOI: Reference:

S1386-1425(15)00167-5 http://dx.doi.org/10.1016/j.saa.2015.02.015 SAA 13305

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

8 August 2014 7 January 2015 4 February 2015

Please cite this article as: N. Karthikeyan, J. Joseph Prince, S. Ramalingam, S. Periandy, Spectroscopic [FT-IR and FT-Raman] and theoretical [UV-Visible and NMR] analysis on α-Methylstyreneby DFT calculations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa. 2015.02.015

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Spectroscopic [FT-IR and FT-Raman] and theoretical [UV-Visible and NMR] analysis on α-Methylstyrene by DFT calculations N. Karthikeyan a, J. Joseph Prince b, S. Ramalingam* c, S. Periandy d a

Department of physics, Indra Ganesan College of Engineering, Trichy, Tamilnadu, India.

b

Department of Physics, Anna University, Bit Campus, Tiruchirappalli, Tamilnadu, India.

c

Department of Physics, A.V.C. College, Mayiladuthurai, Tamilnadu, India.

d

Department of Physics, Tagore Arts College, Puducherry, India. ABSTRACT In the present research work, the FT-IR, FT-Raman and 13C & 1H NMR spectra of the α-

Methylstyrene were recorded. The observed fundamental frequencies in finger print as well as functional group regions were assigned according to their uniqueness region. The Gaussian computational calculations are carried out by HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets and the corresponding results were tabulated. The impact of the presence of vinyl group in phenyl structure of the compound is investigated. The modified vibrational pattern of the molecule associated vinyl group was analyzed. Moreover, 13C NMR and 1H NMR were calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP methods and the 6-311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation between the base and ligand. Besides frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) was performed. The NLO properties related to Polarizability and hyperpolarizability based on the finite-field approach were also discussed. Keywords: α-Methylstyrene; Vinyl group; Optical properties; GIAO; Chemical shifts; FMO. * Corresponding author. Tel.: +91 9003398477; fax: +04364 222264; e-mail: [email protected] 1

1. Introduction α -Methylstyrene has a methyl group and a vinyl group at α position on the ring and it can serve as a model system for studying the substitution effect on benzene. The methyl group can donate electron to the aromatic ring through σ bond, and the vinyl group can share the π electron with the ring [1]. It is also a good model system for studying the “through ring” interaction of the methyl group and vinyl group by their respective torsional potentials. The α-Methylstyrene (AMS) is a chemical intermediate used in the manufacture of plasticizers, resins and polymers. It is a co-product formed in a variation of the cumene process. The homopolymer obtained from this monomer, poly(α-Methylstyrene), is unstable, being characterized by a low ceiling. The polymerization and copolymerization reactions of AMS are very much influenced by its stereochemistry. Normally the alpha–Methylstyrene polymerization is slow because of the formation of a stable radical, which consequently generates polymers with low molecular weight [2]. Alpha methylstyrene is an intermediate that provides higher thermal performance and impact strength to resins-either directly or as an additive. It is used in acrylonitrile butadiene styrene (ABS), coatings, adhesives, acrylic resins, waxes, and various other applications. The AMS is used in coatings and adhesives as a plasticizer for paints and coatings. AMS modifies reaction rates and improves clarity in acrylic resins. In addition, it is used as a chain terminator in polycarbonate resins. It is a UV stabilizer and antioxidant intermediate. Other applications include perfumery chemicals, drying oils, lubricating oils, alkyd resins, and modified phenolic resins. Styrene and its derivatives are the constituents of many important functional polymeric materials. For example, styrene is one of the building units of poly(p-phenylene) [3] and poly(pphenylenevinylene) [4], which are known to have electroluminescent and semiconducting properties. So, studies on the structures, physico-chemical and electro-optical properties of this molecule are very imperative to bring it out industrially. The literature survey reveals that, to the best of our knowledge, no intensive observation of spectroscopic [FT-IR and FT-Raman] and theoretical [HF/DFT] investigation has been reported so far. Therefore, the present investigation was undertaken to investigate the vibrational spectra, geometrical frame work review, inter and intra molecular interaction between HOMO 2

and LUMO energy levels and first order hyperpolarizability of non linear optical (NLO) activity of the molecule.

2. Computational methods Generally, the methodological investigation of vibrational spectroscopy along with quantum computational calculations is a potent tool for the thoughtful of fundamental vibrational behavior of a molecule. In the present work, HF and some of the hybrid methods; B3LYP and B3PW91 were carried out using the basis sets 6-31++G(d,p) and 6-311++G(d,p). All these calculations were performed using GAUSSIAN 09W [5] program package on Pentium IV processor in personal computer. In DFT methods; Becke’s three parameter hybrids function combined with the Lee-Yang-Parr correlation function (B3LYP) [6-7], Becke’s three parameter exact exchangefunction (B3) [8] combined with gradient-corrected correlational functional of Lee, Yang and Parr (LYP) [9-10] and Perdew and Wang (PW91) [11-12] predict the best results for molecular geometry and vibrational frequencies for moderately larger molecules. The calculated frequencies are scaled down to yield the coherent with the observed frequencies. The scaling factors are 0.916, 0.904 and 0.890 for HF/6-311++G(d,p) method. For B3LYP/6-31++/6311++G(d,p) basis set, the scaling factors are 0.962, 0.945, 0.980 and 0.920 /0.975, 0.982, 0.958 and 0.905. For B3PW91/6-311+G(d,p) basis set, the scaling factors are 0.955,0.940, 0.970 and 0.840. The observed (FT-IR and FT-Raman) and calculated vibrational frequencies and vibrational assignments are submitted in Table 2. Experimental and simulated spectra of IR and Raman are presented in the Figures 2 and 3, respectively. The 1H and

13

C NMR isotropic shielding are calculated with the GIAO method [13] using

the optimized parameters obtained from B3LYP/6-311++G(d,p) method. 13C isotropic magnetic shielding (IMS) of any X carbon atoms is made according to value

13

C IMS of TMS,

CSX=IMSTMS-IMSx. The 1H and 13C isotropic chemical shifts of TMS at B3LYP methods with 6311++G(d,p) level using the IEFPCM method in DMSO and CCl4. The absolute chemical shift is found between isotropic peaks and the peaks of TMS[14]. The electronic properties; HOMO-LUMO energies, absorption wavelengths and oscillator strengths are calculated using B3LYP method of the time-dependent DFT (TD-DFT) [15-16], 3

basing on the optimized structure in gas phase and solvent [DMSO, chloroform and CCl4] mixed phase. Thermodynamic properties have been calculated at 298.15ºC in gas phase using B3LYP/6-311++G(d,p) method. Moreover, the dipole moment, nonlinear optical (NLO) properties, linear polarizabilities and first hyperpolarizabilities and chemical hardness have also been studied. 3. Experimental details The compound AMS is purchased from Sigma–Aldrich Chemicals, USA, which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FT-IR spectrum of the compound is recorded in Bruker IFS 66V spectrometer in the range of 4000–400 cm−1. The spectral resolution is ±2 cm−1. The FT-Raman spectrum of AMS is also recorded in the same instrument with FRA 106 Raman module equipped with Nd:YAG laser source operating at 1.064 µm line widths with 200 mW power. The spectra are recorded in the range of 4000–100 cm−1 with scanning speed of 30 cm−1 min−1 of spectral width 2 cm−1. The frequencies of all sharp bands are accurate to ±1 cm−1. The 13C 1H NMR spectrum is recorded by Spin solve high resolution bench top FT-NMR Spectrometer. The operating frequency: 42.5 MHz Proton with Resolution: 50% line width, < 25 ppb (1 Hz) in Sensitivity is greater than 10000:1.

4.

Results and discussion

4.1. Molecular geometry The molecular structure of α-Methylstyrene belongs to CS point group symmetry. The molecular structure is optimized by Berny’s optimization algorithm using Gaussian 09 and Gauss view program and is shown in Figure 1. The comparative optimized structural parameters such as bond length, bond angle and dihedral angle are presented in Table 1. The present molecule contains methyl and vinyl groups. The structure optimization and zero point vibrational energy of the compound in HF and DFT(B3LYP/B3PW91) with 6-31++/6-311++G(d,p) are 107.41, 101.29, 100.88, 101.46 and 101.03 Kcal/Mol, respectively. The calculated energy of HF is greater than DFT method because the assumption of ground state energy in HF is greater than the true energy. Though, the benzene ring belongs to one plane, the substitutions belongs to multiple planes. The hexagonal structure 4

of the base molecule is broken due to the coupling of CH3-C=CH2 groups. The bond lengths of C1-C2 and C1-C6 are just pulled up by loading of substitution in the benzene ring. Thus the hexagonal ring is broken in favor of substitution. The other bond length in benzene ring is nearly equal. The bond angle of C2-C1-C6 is reduced by 0.010º than C3-C4-C5 due to the presence of CH3-C=CH2 group in the pedestal molecule. The entire C-H bonds in the ring having almost equal inter nuclear distance. Form the optimized molecular structure; it is observed that the functional group belongs to multiple planes. 4.2. Vibrational assignments In order to obtain the spectroscopic signature of the AMS, the computational calculations are carried out for frequency analysis. The molecule is indentified with CS point group symmetry, consists of 19 atoms, so it has 51 normal vibrational modes. On the basis of Cs symmetry, the 51 fundamental vibrations of the molecule can be distributed as 34 in-plane vibrations of A species and 17 out of plane vibrations of A species, i.e., vib = 34 A + 17 A. In the CS group symmetry of molecule is non-planar structure and has the 51 vibrational modes span in the irreducible representations. The harmonic vibrational frequencies (unscaled and scaled) calculated at HF, B3LYP and B3PW91 levels using the triple split valence basis set along with the diffuse and polarization functions; 6-31++ G(d,p) and 6-311++G(d,p) and observed FT-IR and FT-Raman frequencies for various modes of vibrations have been presented in Tables 2 and 3. The inclusion of electron correlation in the density functional theory to certain extends makes the frequency values better than the HF frequency data. 4.2.1. C-H vibrations The aromatic compounds, particularly, the benzene and its derivative compounds commonly exhibit multiple weak bands in the region 3000-3100 cm-1 due to the C-H bond stretching vibrations[17-19]. The present compound AMS, posses five C-H bonds and their stretching vibrations are observed with strong intensity at 3065, 3060, 3040, 3010 and 2980 cm-1 in IR and Raman spectra. Except one peak, the entire observed bands are distributed within the allowed region. This is because of the influence of vinyl group with dominant character. The C-H in plane ring bending vibrations normally occurred as a number of strong to weak intensity sharp bands in the region 1300-1000 cm-1 [20]. The bands for C-H in plane 5

bending vibrations are identified at 1190, 1160, 1110, 1070 and 1030 cm-1. All the bands found at the lower corner of the expected region with weak and medium intensity and also the peaks are present in IR and Raman. All the observed peaks are originated at tail end of the predictable region. Normally, the C-H out of plane bending vibrations are observed in the region 950-760 cm-1 [21-23]. In the present case, the out of plane bending bands are identified at 840, 780, 760, 750 and 740 cm-1. Unlike in plane bending, two bands are moved down from out of the allowed region. This is purely due to the effect of the substitutions in the ring. Except out of plane bending vibrations, the assigned frequencies for C-H vibrations are found to be well within their characteristic regions. As a result from above discussion, it is infer that C-H out of plane bending vibrations have been affected by the substitutions. 4.2.2. C-C vibrations The ring C=C and C-C stretching vibrations, known as semicircle stretching usually occur in the region 1400-1625 cm-1 [24-26]. The C=C stretching vibrations of the present compound are strongly observed at 1600, 1570 and 1495 cm-1. These assignments are in line with the literature [27-29]. The C-C stretching vibrations were observed at 1440, 1400 and 1370 cm-1. When compared to the literature range cited above, there is a considerable decrease in observed frequencies and one of them is moved down from the probable range which is also worsening with the increase of mass of substitutions held around the ring. Most of the CC stretching bands are observed with very strong and medium intensity and found in both IR and Raman. Apart from that, three crests present at 490, 370 and 365cm-1 are assigned to CCC in plane bending and three supplementary peaks are assigned at 200, 150 and 120 cm-1 to CCC out of plane bending. The entire bending bands are found away from the expected region which is probably due to the suppression of other vibrations in and around the ring. 4.2.3. Methyl group vibrations The title compound posses a methyl group along with vinyl group and their vibrational assignments ensure the place of methyl group within a molecule. The asymmetric and the symmetric C-H symmetric vibrations in methyl group usually observed between 2990-2920 cm-1, whereas the symmetric C-H vibrations for methyl group are observed at 2900 – 2840 cm-1 [3032]. Being in excellent agreement with the literature, in this study, for AMS, the symmetric C-H vibrations are occurring at 2940, 2915 and 2850 cm-1. There is no asymmetric C-H vibration and also such are not affected by other vibrations. The in plane and out of plane bending vibrations 6

are observed at 1020, 1000 and 950 cm-1 and 620, 545 and 540 cm-1 respectively. From the bending vibrations, it is observed that, except two, the entire vibrations found behind the expected region due to the interaction of vinyl group. Predicted by the DFT calculations, the compounds containing CH3 group, the series of the bands appearing as asymmetric and symmetric deformation modes in the region 1400-1500 cm-1 [33-34] are mainly due to methyl deformation, coupling with the C-H and C-C stretching frequencies, two different extends and in different way. In the present study, the Raman bands at 1460 cm−1 (very strong) and 1450 cm−1 (strong) are attributed to the asymmetric deformation modes of isopropyl group. Appearance of these bands is due to presence of two independent CH3 groups in the amino acid residues in different environments. 4.2.4. Vinyl group vibrations The present compound has one vinyl group along with the methyl group, so the interaction is possible within the molecule. The asymmetric =CH2 stretching of vinyl and vinylidine group (3092-3077cm-1) absorb at a higher frequency than =CH vibration (30503000cm-1) in hydrocarbons [19]. Accordingly, the asymmetric C–H stretching vibrations are located at higher frequency region than those of the aromatic C–H ring stretching which are observed with strong intensity at 3090 and 3070 cm−1. In spite of the presence of CH2 in void position, these stretching peaks have not affected much. Normally, the C-H scissoring mode is very active in ethylene substituted molecules [35]. In the present assignment, for CH2, the C-H scissoring bending modes are found with very strong intensity at 900 and 895 cm-1 and the wagging modes traced at 520 and 495 cm-1. The assignments for bending vibrations are illogical with the literature report [36-38]. This is mainly due to the interaction effect of carbon in the ring. Normally, the C=C stretching frequency is observed near 1640 cm-1 in vinyl group with medium intensity and which becomes interactive in the IR region in a cis-trans or symmetrical tetra substituted double compound[39], both of which have centers of symmetry. The double bond vibrations are usually appeared strongly in the Raman Effect, however, the trans- tri- and tetra alkyl substituted olefin have somewhat higher C=C stretching frequency than cis, vinylidine or vinyl groups[40]. Conjugation, which weakens the C=C force constant, lower the frequency about 10-50 cm-1. Therefore, in the present case, the C=C stretching for vinyl is absorbed with 7

very strong intensity at 1635 cm-1. This observation is in line with the literature. The corresponding C-C stretching vibrations for CH3-C-CH2 group are found consistently at 1305 and 1220 cm-1 which are identified in the spectra without disturbance. The C-C in plane and out of plane bending vibrational peaks established at 710 and 690 cm-1 and 250 and 230 cm-1 respectively. The in plane bending bands are positioned correctly within the expected region whereas the out of plane bending pushed down to the lower end of the spectra. 4.3. NMR analysis NMR spectroscopy technique is throwing new light on organic structure elucidation of much difficult complex molecules. The combined use of experimental and computational tools offers a powerful gadget to interpret and predict the structure of bulky molecules. In this way, the optimized structure of AMS is used to calculate the NMR spectra by B3LYP method with 6311++G(d,p) level using the GIAO method and the chemical shifts of the compound are reported in ppm relative to TMS for 1H and

13

C NMR spectra which are presented in Tables 4. The

corresponding spectra are shown in Figure 5. Normally, the range of 13C NMR chemical shifts for is greater than 100 ppm [41-43] and the accuracy ensure that the reliable interpretation of spectroscopic parameters. In the present work, 13

C NMR chemical shifts of entire carbons in and out of the ring are greater than 100 ppm, as in

the expected regions. The present molecule posses hexagonal ring, in which the chemical shift of six carbons are (C1, C2, C3, C4, C5 and C6) are 111.10, 73.62, 85.96, 82.59, 85.03 and 72.18 ppm respectively. Except C1, the chemical shift entire carbons in the ring are less than 100 ppm. The chemical shift of C1 is more than rest of others. This is mainly due to the breaking of paramagnetic shield of proton by the substitutions of CH3-C=CH2. This view ensured that, the existence of substitutional groups in the molecule and thus chemical property of the ring is changed on par with the substitutions. The C12 and C16 in the chain have more shifted than C13 due to the delocalization of σ and π electrons by CH3 group. The shift of the carbons of C3, C4 and C5 of the ring is found nearly equal when compared with C2 and C6. The shift of H in the benzene ring is less than the H of methyl group due to the further substitutions in the chain. From the observation, it is clear that the change of chemical property of benzene is only in favor of H2C=C-CH3 groups. In addition to that, due to the accessibility of this group, the property of the entire molecule is depends upon 8

the substitutions in the compound. There is no considerable difference chemical shift between gas and solvent phases. 4.4. Electronic properties (frontier molecular analysis) The frontier molecular orbitals are very much useful for studying the electric and optical properties of the organic molecules. The stabilization of the bonding molecular orbital and destabilization of the antibonding can be made by the overlapping of molecular orbitals. The stabilization of the bonding molecular orbital and destabilization of the antibonding can increase when the overlap of two orbitals increases [44]. In the molecular interaction, there are the two important orbitals that interact with each other. One is the highest energy occupied molecular orbital is called HOMO represents the ability to donate an electron. The other one is the lowest energy unoccupied molecular orbital is called LUMO as an electron acceptor. These orbitals are sometimes called the frontier orbitals. The interaction between them is much stable and is called filled empty interaction. When the two same sign orbitals overlap to form a molecular orbital, the electron density will occupy at the region between two nuclei. The molecular orbital resulting from in-phase interaction is defined as the bonding orbital which has lower energy than the original atomic orbital. The out of phase interaction forms the anti bonding molecular orbital with the higher energy than the initial atomic orbital. The orbital interactions are depending on their symmetry. It is stated that, the orbital interactions are allowed if the symmetries of the atomic orbitals are compatible with one another. Under the symmetry’s affect, the result of orbital interaction from anti bonding is nonbonding to bonding. Based on the symmetry, the orbital interactions from bonding are classified as σ, π and δ bonding. The 3D plots of the frontier orbitals; HOMO and LUMO of AMS molecule for are in gas, shown in Figure 4. According to Figures 4, In the present compound, the HOMO and HOMO+1 are shaped by the π orbital bonding interaction and the HOMO is mainly localized over the C=C of the upper and lower moieties of benzene ring and the vinyl group. The HOMO+1 is mainly localized over the C=C of the left and right moieties of benzene ring itself. The LUMO and LUMO-1 are wrought by the σ orbital bonding interaction and the LUMO is mainly localized over the C-C and C-H of the hexagonal ring and the vinyl group. The LUMO-1 is mainly localized over the C-H of the left and right moieties of benzene ring itself. 9

The antibonding orbital lobes are also taking place over some part of the molecule. From this observation, it is clear that, the in and out of phase interaction, π orbital and σ orbital bonding interaction are present in HOMO and LUMO respectively. The HOMO→LUMO transition implies an electron density transferred among ring and vinyl group. The HOMO and LUMO energy are 9.3261 eV and 5.0724 eV in gas phase (figure 4). Energy difference between HOMO and LUMO orbital is called as energy gap (kubo gap) that is an important stability for structures. The DFT level calculated energy gap is 4.2537 eV, show the large energy gap and reflect the dull electrical activity of the molecule. 4.5. Optical properties (HOMO-LUMO analysis) The UV and visible spectroscopy is used to detect the presence of chromophores in the molecule and whether the compound has NLO properties or not. The electronic structure calculations of AMS are optimized in singlet state. The low energy electronic excited states of the molecule are calculated at the B3LYP/6-311++G(d,p) level using the TD-DFT approach on the previously optimized ground-state geometry of the molecule. The calculations are performed in gas phase and with the solvent of DMSO, CCl3 and CCl4. The calculated excitation energies, oscillator strength (f) and wavelength (λ) and spectral assignments are given in Table 5 and the corresponding 3D plots of the frontier orbitals is outlined in figure 7. The major contributions of the transitions are designated with the aid of SWizard program [45]. The aromatic system contains p electrons, absorb strongly in the ultraviolet. In general, the greater the length of a conjugated system in a molecule, the nearer the λmax comes to the visible region. Thus, the characteristic energy of a transition and hence the wavelength of absorption is a property of a group of atoms rather than the electrons themselves. The TD-DFT calculations predict that, irrespective of the gas and solvent phase, the entire transitions belong to quartz ultraviolet region. In the case of gas phase, the strong transition is at 266.07, 257.37 and 220.26 nm with an oscillator strength f=0.14, 0.09 and 0.20 with 4.65, 4.81 and 5.62 eV energy gap. The transition is n→π* in quartz ultraviolet region. The designation of the band is R-band (German, radikalartig) which is attributed to above said transition due to the addition of auxochromes with chromophoric group, such as H3C-C=CH2 group. They are characterized by low molar absorptivities (ξmax<100) and undergo hypsochromic to bathochromic shift and the solvent effect is inactive in this compound. The simulated UV-Visible spectra in gas and solvent phase are 10

shown in Figure 6. In DMSO solvent, strong transitions are 269.58, 258.11, 226.70 and 222.51nm with an oscillator strength f=0.26, 0.06, 0.008 and 0.28 with maximum energy gap 5.57 eV. They are assigned to n → π* transition and belongs to quartz ultraviolet region. This shows that, from gas to solvent, the electronic transitions do not shift from quartz ultraviolet region. This view indicates that, the AMS molecule is UV active and it is capable of having rich biological properties. In addition, the calculated optical band gap 3.57 eV which also ensure that the present compound possessing biological as well as NLO properties. In view of calculated absorption spectra, the maximum absorption wavelength corresponds to the electronic transition from the HOMO+1 to LUMO-1 with maximum contribution. In this present compound, the chromophores is vinyl group along with CH3, the industrial properties are enhanced in the present compound. The total electronic transition of the compound is shifted hypsochromic to bathochromic region which indicate that the influence of the substitutional group in the present compound. 4.6. Chemical properties The chemical hardness and potential, electronegativity and Electrophilicity index [46] are calculated and their values are shown in Table 6. The chemical hardness is a good indicator of the chemical stability. The chemical hardness is nearly equal (2.51-2.52) in going from gas to solvent. Therefore, the present compound has much chemical stability. The substitutions of H3CC=CH2 group enhanced the chemical stability and acid character of the compound. Similarly, the electronegativity is increased from 3.73 up to 3.85, from Gas to solvent, if the value is greater than 1.7; the property of chemical bonds in the molecule is changed from covalent to ionic. Accordingly, due to the addition of vinyl group, the bonds character of the compound rehabilitated to ionic. Electrophilicity index is a factor which is used to measure the energy lowering due to maximal electron flow between donor [HOMO] and acceptor [LUMO]. From the Table 6, it is found that the Electrophilicity index is 2.77 in gas and 2.94 in DMSO solvent, which is high and this value ensures that the strong energy transformation is taking place between HOMO+1 and LUMO-1 instead of HOMO-LUMO. The dipole moment in a molecule is another important electronic property. Whenever the molecule would have possessing large dipole moment, the intermolecular interactions is very strong. The calculated dipole moment value for the title compound is 0.35 Debye in gas and 0.48 in DMSO solvent. It is very much low 11

which is inferred that, the present molecule has less effective intermolecular interactions. 4.7. Molecular electrostatic potential (MEP) maps The molecular electrical potential surfaces illustrate the charge distributions of molecules three dimensionally. This map allows us to visualize variably charged regions of a molecule. Knowledge of the charge distributions is much useful to determine how molecules interact with protein and it is also be used to determine the requirement of minimum energy to bind with protein structure [47]. Molecular electrostatic potential view is mapped up at the level of B3LYP/6-311++G(d,p) theory with optimized geometry. There is a great deal of intermediary potential energy, the non red or blue region indicate that the electro negativity difference is not very great. In a molecule with a great electro negativity difference, charge is very polarized in negative and positive form, and there are significant differences in electron density in different regions of the molecule. This great electro negativity difference leads to regions that are almost entirely red and almost entirely blue. The region of intermediary potential is explored by yellow and green color and the regions of extreme potential look at red and blue colors are key indicators of electronegativity. The color code of these maps is in the range between -8.459 e-3 a.u. (deepest red) to 8.459e-3 a.u. (deepest blue) in compound. The positive (blue) regions of MEP are related to electrophilic reactivity and the negative (green) regions to nucleophilic reactivity shown in Figure 8. As can be seen from the MEP map of the title molecule, the negative regions are mainly localized on the core of the ring. A maximum positive region is localized on the over the H of ring and vinyl group indicating a possible site for nucleophilic attack. The molecule contains no electronegative atoms with benzene ring, the positive and negative potential regions located at hub and exterior of benzene ring. From these results, it is inferred that, when the compound docked with protein structure, the H3C-C=CH2 group in the molecule act as main root to bind. 4.8. Polarizability and First order hyperpolarizability calculations In order to investigate the relationships among the molecular structures, non-linear optic properties (NLO) and molecular binding properties, the polarizabilities and first order hyperpolarizabilities of the present compound are calculated using DFT-B3LYP method and 6311++G(d,p) basis set, based on the finite-field approach.

12

The Polarizability and hyperpolarizability is obtained from the output file of Polarizability and hyperpolarizability calculations. However, α and β values of Gaussian output are in atomic units (a.u.) have been converted into electronic units (esu) (α; 1 a.u. = 0.1482×10−24 esu, β; 1 a.u. = 8.6393×10−33 esu. In Table 7, the calculated parameters described above and electronic dipole moment {μi (i = x, y, z) and total dipole moment  tot } for title compound are listed. The total dipole moment is be calculated using the following equation

tot   x2   y2   z2 2 1

It is well known that, molecule with high values of dipole moment, molecular Polarizability, and first hyperpolarizability having more active NLO properties. The first hyperpolarizability () and the component of hyperpolarizability x, y and z of AMS along with related properties (0, total, and Δ) are reported in Table 7. The calculated value of dipole moment is found to be 0.3525 Debye. The highest value of dipole moment is observed in the component of μZ which is 0.134 D. The lowest value of the dipole moment of the molecule compound is μz component (0.007 D). The calculated average Polarizability and anisotropy of the polarizability is 142.11x1024

esu and 206.57x10−24 esu, respectively. The magnitude of the molecular hyperpolarizability ,

is one of important key factors in a NLO system. The B3LYP/6-311+G(d,p) calculated first hyperpolarizability value () is 48.92x10−30 esu. From the above results, it is observed that, the molecular Polarizability and hyperpolarizability of the title compound in two perpendicular coordinates are active. So that, the present compound can be used to prepare NLO crystals and those crystal is able to produce second order harmonic waves with more amplitude. Apart from that, due to the elevated values of Polarizability and hyperpolarizability, the present compound is able to bind with other molecules with less amount of binding energy.

5. Conclusion In the present investigation, the FT-IR and FT-Raman spectral analysis was made on αMethylstyrene. The observed vibrational frequencies were assigned depending upon their expected region. The chronological change of finger print and group frequency region of the 13

benzene with respect to the functional group H3C-C=CH2 has also been monitored. The change of geometrical parameters along with the substitutions is deeply analyzed. The simulated

13

C

NMR and 1H NMR spectra in gas and solvent phase are displayed and the chemical shifts are studied. The electrical and optical and bio molecular properties are profoundly investigated using frontier molecular orbital. The UV-Visible spectra indicate that, the entire electronic transitions shifted bathochromically due to the substitutional effect. It is also found that the present compound is optical and bio active and also posses NLO properties. The molecular electrostatic potential (MEP) map is performed and from which the change towrds the chemical properties of the compound is also discussed.

Acknowledgement The authors thank all the officials of academic and non academics of Anna University, Bit Campus, Tiruchirappalli, Tamilnadu, India.

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17

Fig. 1. Molecular structure of α-Methylstyrene

Fig. 2. Experimental [A] and calculated [B, C and D] FT-IR spectra of α-Methylstyrene

Fig. 3. Experimental [A] and calculated [B, C and D] FT-Raman spectra of α-Methylstyrene

Fig. 4. HOMO and LUMO molecular orbital view of α-Methylstyrene

Fig. 5. Calculated 13C and 1H spectra of α-Methylstyrene

Fig. 6. Calculated UV-Visible spectra of α-Methylstyrene

Fig. 7. HOMO and LUMO orbitals in UV-Visible region

Fig. 8. Molecular electrostatic potential and contour map of α-Methylstyrene

Table 1. Optimized geometrical parameters for α-Methylstyrene computed at HF/DFT (B3LYP&B3PW91) with 6-31++G(d,p) & 6-311++G(d, p) basis sets Geometrical Parameters

Bond length(Å) C1-C2 C1-C6 C1-C12 C2-C3 C2-H7 C3-C4 C3-H8 C4-C5 C4-H9 C5-C6 C5-H10 C6-H11 C12-C13 C12-C16 C13-H14 C13-H15 C16-H17 C16-H18 C16-H19 Bond angle(˚) C2-C1-C6 C2-C1-C12 C6-C1-C12 C1-C2-C3 C1-C2-H7 C3-C2-H7

Methods HF 6-311++G (d, p)

B3LYP 6-31++G 6-311++G (d, p) (d, p)

B3PW91 6-311++G (d, p)

1.392 1.392 1.495 1.384 1.074 1.385 1.075 1.384 1.075 1.385 1.075 1.074 1.324 1.510 1.076 1.075 1.086 1.083 1.086

1.403 1.404 1.488 1.393 1.083 1.392 1.084 1.394 1.084 1.391 1.084 1.083 1.339 1.511 1.084 1.083 1.094 1.091 1.094

1.395 1.397 1.467 1.385 1.093 1.384 1.093 1.388 1.093 1.381 1.093 1.094 1.337 1.487 1.093 1.093 1.103 1.099 1.104

1.400 1.402 1.484 1.390 1.084 1.390 1.085 1.392 1.085 1.388 1.085 1.084 1.338 1.505 1.085 1.084 1.094 1.091 1.095

118.149 121.098 120.752 120.945 120.040 119.005

117.742 121.189 121.067 121.137 119.911 118.943

117.770 120.545 121.681 121.186 119.455 119.356

117.818 121.170 121.009 121.101 119.866 119.024

C2-C3-C4 C2-C3-H8 C4-C3-H8 C3-C4-C5 C3-C4-H9 C5-C4-H9 C4-C5-C6 C4-C5-H10 C6-C5-H10 C1-C6-C5 C1-C6-H11 C5-C6-H11 C1-C12-C13 C1-C12-C16 C13-C12-C16 C12-C13-H14 C12-C13-H15 H14-C13-H15 C12-C16-H17 C12-C16-H18 C12-C16-H19 H17-C16-H18 H17-C16-H19 H18-C16-H19 Dihedral angles(˚) C6-C1-C2-C3 C6-C1-C2-H7 C12-C1-C2-C3 C12-C1-C2-H7 C2-C1-C6-C5 C2-C1-C6-H11 C12-C1-C6-C5 C12-C1-C6-H11

120.294 119.632 120.072 119.360 120.302 120.336 120.273 120.090 119.635 120.969 119.427 119.596 121.136 117.294 121.566 121.270 121.862 116.861 110.643 110.785 111.430 108.691 107.264 107.893

120.314 119.615 120.070 119.310 120.349 120.337 120.304 120.052 119.639 121.176 119.316 119.490 121.565 117.676 120.757 121.131 122.141 116.716 111.195 110.785 111.549 108.597 106.980 107.563

120.212 119.702 120.084 119.350 120.355 120.291 120.309 119.997 119.688 121.157 119.244 119.580 122.077 117.381 120.532 120.720 122.178 117.090 111.480 110.908 111.331 108.706 106.613 107.613

120.301 119.629 120.069 119.333 120.337 120.327 120.287 120.058 119.648 121.142 119.237 119.602 121.398 117.672 120.927 121.099 122.022 116.865 111.193 110.838 111.490 108.634 106.987 107.528

-1.0918 -179.99 179.03 0.1371 0.8374 -178.18 -179.28 1.6914

-1.429 179.58 178.89 -0.089 1.2556 -177.29 -179.068 2.3858

-1.3725 179.2155 179.1629 -0.249 1.2842 -177.1666 -179.2577 2.2915

-1.46 179.55 178.93 -0.046 1.29 -177.17 -179.10 2.4269

C2-C1-C12-C13 C2-C1-C12-C16 C6-C1-C12-C13 C6-C1-C12-C16 C1-C2-C3-C4 C1-C2-C3-C8 H7-C2-C3-C4 H7-C2-C3-H8 C2-C3-C4-C5 C2-C3-C4-H9 H8-C3-C4-C5 H8-C3-C4-H9 C3-C4-C5-C6 C3-C4-C5-H10 H9-C4-C5-C6 H9-C4-C5-H10 C4-C5-C6-C1 C4-C5-C6-H11 H10-C5-C6-C1 H10-C5-C6-H11 C1-C12-C13-H14 C1-C12-C13-H15 C16-C12-C13-H14 C16-C12-H13-H15 C1-C12-C16-H17 C1-C12-C16-H18 C1-C12-C16-H19 C13-C12-C16-H17 C13-C12-C16-H18 C13-C12-C16-H19

-135.28 45.188 44.84 -134.68 0.6875 -179.24 179.59 -0.338 -0.00 179.67 179.93 -0.394 -0.252 179.281 -179.92 -0.389 -0.176 178.84 -179.71 -0.695 -178.75 2.132 0.7563 -178.36 55.41 176.03 -63.82 -124.10 -3.48 116.64

-147.32 32.25 33.011 -147.40 0.7398 -179.3247 179.7341 -0.3303 0.1701 179.604 -179.7651 -0.3312 -0.3431 178.88 -179.777 -0.544 -0.389 178.15 -179.62 -1.0817 -178.79 2.4204 1.635 -177.14 53.31 174.18 -66.01 -127.09 -6.230 113.566

-161.4045 17.5057 19.1522 -161.9376 0.611 -179.564 -179.9765 -0.1515 0.281 179.6261 -179.5434 -0.1982 -0.3683 178.7968 -179.7139 -0.5487 -0.434 178.0117 -179.6017 -1.156 -179.2009 2.0349 1.9226 -176.8416 53.6613 174.9467 -65.2549 -127.4108 -6.1254 113.673

-147.15 32.366 33.25 -147.22 0.7499 -179.31 179.73 -0.330 0.176 179.59 -179.75 -0.3355 -0.3452 178.8 -179.76 -0.5664 -0.4069 178.056 -179.60 -1.1443 -178.81 2.513 1.6879 -176.9 52.8581 173.8072 -66.4446 -127.6219 -6.6728 113.0754

Table 2. Observed and HF and DFT (B3LYP & B3PW91) with 6-31++G(d,p) & 6-311++G (d,p) level calculated vibrational frequencies of α-Methylstyrene

S. No 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

Symmetry Species CS A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A″ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′ A′

observed frequency(cm-1) FT-IR 3090s 3065s 3040vs 3010s 2940vs 2915vs 2850w 1635vs 1600vs 1570s 1495vs 1445vs 1440vs 1370vs 1305vs 1220vw 1190w 1160w 1110w 1070m 1020vs 1000s

FTRaman 3070s 3065s 3060s 2980vs 2915vs 2850w 1635vs 1600vs 1495s 1440m 1400vs 1370w 1305vs 1190m 1160m 1110vs 1030m 1000vs

HF 6-311++G (d,p) 3084 3070 3066 3059 3046 3037 2971 2934 2907 2862 1657 1615 1585 1492 1435 1425 1413 1386 1364 1298 1263 1172 1149 1088 1069 1044 1032

Methods B3LYP 6-311++G 6-311++G (d,p) (d,p) 3098 3084 3071 3069 3066 3060 3059 3054 3048 3046 3040 3020 2966 2998 2936 2936 2900 2893 2856 2835 1617 1636 1606 1604 1580 1574 1495 1490 1440 1441 1453 1417 1392 1399 1360 1370 1298 1289 1247 1215 1223 1177 1199 1159 1111 1113 1087 1089 1045 1004 1019 1039 980 996

B3PW91 6-311++G (d,p) 3088 3058 3052 3046 3035 3027 3005 2939 2904 2850 1641 1604 1576 1480 1443 1433 1405 1368 1275 1238 1219 1196 1096 1073 1034 1009 995

Vibrational Assignments (C-H)(CH2) υ (C-H) (CH2)υ (C-H) υ (C-H) υ (C-H) υ (C-H) υ (C-H) υ (C-H) (CH3) υ (C-H) (CH3)υ (C-H) (CH3) υ (C=C) υ (C=C) υ (C=C) υ (C=C) υ (CH3) α (C-C) υ (C-C) υ (C-C) υ (C-C) υ (C-C) υ (C-H) δ (C-H) δ (C-H) δ (C-H) δ (C-H) δ (C-H)(CH3) δ (C-H)(CH3) δ

28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

A′ A′ A′ A′ A′ A″ A″ A″ A″ A″ A″ A″ A″ A″ A″ A′ A′ A′ A″ A″ A″ A″ A″ A″

950vw 900vs 895vs 840w 780vs 750vs 740vs 710vs 690w 620m 545s 540s 520m 495w 490w 370s 365s 250w 230w 200w 150m 120w 110w

950w 900w 840w 780m 760vs 690m 620m 520w 490vw 250w 150m -

994 991 984 769 756 733 724 699 662 608 554 550 536 473 428 398 387 316 278 251 164 141 104 32

965 939 934 921 738 704 698 692 639 597 560 538 525 476 421 415 373 311 287 263 172 143 107 45

971 900 875 868 706 740 714 694 653 619 559 517 501 462 403 389 348 299 291 271 184 163 107 27

957 923 923 839 827 791 781 772 716 669 628 601 588 529 470 446 417 346 319 292 190 158 118 44

(C-H)(CH3) δ (C-H) (CH2)δ (C-H) (CH2)δ (C-H) γ (C-H) γ (C-H) γ (C-H) γ (C-H) γ (C-C) δ (C-C) δ (C-H)(CH3) γ (C-H)(CH3) γ (C-H)(CH3) γ (C-H) (CH2)γ (C-H)(CH2) γ (CCC) δ (CCC) δ (CCC) δ (C-C) γ (C-C) γ (CCC) γ (CCC) γ (CCC) γ (CH2) τ

VS –Very strong; S – Strong; m- Medium; w – weak; as- Asymmetric; s – symmetric; υ – stretching; α –deformation, δ - In plane bending; γ-out plane bending; τ – Twisting:

Table 3. Calculated unscaled frequencies by HF/DFT (B3LYP&B3PW91) with 6-31++(d,p) and 6-311++G(d,p) basis sets

S. No

Observed frequency

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

3550 3460 3350 2970 2930 2920 2910 2890 2880 2860 2850 1710 1620 1495 1465 1460 1450 1400 1395 1375 1370 1350 1325 1270 1190

HF 6-311++G (d,p) 3367 3352 3347 3339 3325 3315 3286 3246 3216 3166 1833 1786 1753 1650 1612 1601 1588 1557 1533 1458 1419 1317 1291 1223 1201

Calculated frequency B3LYP 6-31++G 6-311++G (d,p) (d,p) 3220 3163 3192 3125 3187 3116 3180 3110 3168 3102 3160 3097 3139 3075 3107 3065 3069 3020 3022 2959 1681 1666 1639 1633 1612 1603 1525 1490 1497 1441 1483 1417 1473 1399 1439 1395 1411 1364 1355 1343 1329 1301 1303 1281 1208 1162 1182 1137 1136 1109

B3PW91 6-311++G (d,p) 3233 3202 3196 3190 3178 3170 3147 3127 3089 3032 1692 1654 1625 1526 1488 1477 1471 1432 1401 1360 1340 1314 1204 1179 1136

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

1170 1165 1140 1105 1050 995 940 900 870 850 820 720 710 560 500 450 390 360 340 310 280 220 210 200 150 140

1173 1159 1117 1113 1106 1099 1080 1047 1034 999 946 868 792 786 766 676 611 568 553 452 397 359 234 202 148 46

1108 1065 1049 1021 1015 1001 984 938 931 922 852 796 746 717 700 634 561 553 497 415 383 351 229 191 142 46

1085 1040 1014 994 967 959 941 925 893 867 816 774 745 689 668 616 537 519 464 398 388 361 245 217 142 36

1109 1059 1052 1014 1014 999 984 942 930 919 852 796 748 716 700 630 559 531 496 412 380 348 226 188 141 45

Table 4. Calculated 1H and 13C NMR chemical shifts (ppm) of α-Methylstyrene

Atom position

C1 C2 C3 C4 C5 C6 C12 C13 C16 H7 H8 H9 H10 H11 H14 H15 H17 H18 H19

TMS B3LYP/ B3LYP/66-311+G 311+G (d,p) (2d,p) (ppm) GIAO (ppm) Gas 35.68 146.78 54.42 128.04 48.25 134.21 49.93 132.52 48.71 133.74 55.14 127.32 23.44 159.02 67.83 114.63 167.38 15.08 24.36 7.51 24.56 7.31 24.70 7.17 24.56 7.31 23.64 8.23 26.71 5.16 25.53 6.35 30.16 1.71 30.47 1.40 30.48 1.39

Shift (ppm)

111.10 73.62 85.96 82.59 85.03 72.18 135.58 46.80 152.30 16.85 17.25 17.53 17.25 15.41 21.55 19.18 28.45 29.07 29.09

TMS B3LYP/ B3LYP/66-311+G 311+G (d,p) (2d,p) (ppm) GIAO (ppm) 35.92 53.77 47.75 49.39 48.35 55.12 22.23 67.81 167.48 24.16 24.38 24.52 24.39 23.49 26.57 25.42 30.07 30.36 30.42

DMSO 146.54 128.69 134.70 133.06 134.11 127.34 160.22 114.65 14.98 7.71 7.49 7.35 7.48 8.39 5.30 6.45 1.81 1.51 1.45

Shift (ppm)

110.62 74.92 86.95 83.67 85.76 72.22 137.99 46.84 152.50 16.45 16.89 17.17 16.91 15.10 21.27 18.97 28.26 28.85 28.97

TMS B3LYP/ B3LYP/66-311+G 311+G (d,p) (2d,p) (ppm) GIAO (ppm) 35.80 53.98 47.94 49.59 48.48 55.10 22.54 67.89 167.45 24.22 24.44 24.58 24.45 23.54 26.62 25.46 30.10 30.39 30.44

Shift (ppm)

Chloroform 146.65 110.85 128.48 74.50 134.52 86.58 132.87 83.28 133.97 85.49 127.36 72.26 159.91 137.37 114.56 46.67 15.00 152.45 7.65 16.57 7.44 17.00 7.29 17.29 7.43 17.02 8.34 15.20 5.26 21.36 6.41 19.05 1.78 28.32 1.48 28.91 1.43 29.01

TMS B3LYP/ B3LYP/66-311+G 311+G (d,p) (2d,p) (ppm) GIAO (ppm) 35.66 54.34 48.12 49.60 48.57 55.21 22.37 67.45 167.33 24.27 24.47 24.60 24.53 23.63 26.63 25.48 30.12 30.43 30.43

CCl4 146.80 128.12 134.33 132.85 133.89 127.25 160.09 115.01 15.12 7.60 7.40 7.28 7.35 8.24 5.24 6.39 1.75 1.44 1.44

Shift (ppm)

111.14 73.78 86.21 83.25 85.32 72.04 137.72 47.56 152.21 16.67 17.07 17.32 17.18 15.39 21.39 19.09 28.37 28.99 28.99

Table 5. Theoretical electronic absorption spectra of α-Methylstyrene (absorption wavelength λ (nm), excitation energies E (eV) and oscillator strengths (f)) using TD-DFT/B3LYP/6-311++G(d,p) method λ (nm)

E (eV)

Gas 266.07 4.659 257.37 4.817 232.55 5.331 220.26 5.629 DMSO 269.58 4.599 258.11 4.803 226.70 5.469 222.51 5.572 Chloroform 269.97 4.592 258.46 4.797 228.46 5.427 222.84 5.563 CCl4 270.21 4.588 258.73 4.792 230.18 5.386 223.05 5.558

(f)

Major contribution

Assignment

Region

Bands

0.1484 0.0994 0.0042 0.2092

HL (92%) HL (89%) HL-1 (86%) H+1L (86%)

n→π* n→π* n→π* n→π*

Quartz UV Quartz UV Quartz UV Quartz UV

0.2636 0.0652 0.0083 0.2875

HL (90%) HL-1 (90%) HL-1 (87%) H+1L-1 (83%)

n→π* n→π* n→π* n→π*

Quartz UV Quartz UV Quartz UV Quartz UV

R-band (German, radikalartig)

0.2702 0.0634 0.0070 0.2917

HL (86%) HL-1 (85%) H+1L (78%) H+1L-1(77%)

n→π* n→π* n→π* n→π*

Quartz UV Quartz UV Quartz UV Quartz UV

R-band (German, radikalartig)

H: HOMO; L: LUMO 0.2735 HL (86%) 0.0624 HL-1 (85%) 0.0061 H+1L (78%) 0.2936 H+1L-1(74%)

n→π* n→π* n→π* n→π*

Quartz UV Quartz UV Quartz UV Quartz UV

R-band (German, radikalartig)

R-band (German, radikalartig)

Table 6. Calculated energies values, chemical hardness, electro negativity, Chemical potential, Electrophilicity index of α-Methylstyrene from UV-Visible region

TD-DFT/B3LYP/ 6-311G++(d,p) Etotal (Hartree) EHOMO (eV) ELUMO (eV) EHOMO-LUMO gap (eV) EHOMO-1 (eV) ELUMO+1 (eV) EHOMO-1-LUMO+1 gap (eV) Chemical hardness () Electronegativity (χ) Chemical potential (μ) Chemical softness(S) Electrophilicity index (ω) Dipole moment

Gas

DMSO

Ethanol

Methanol

-349.04 6.2556 1.2185 5.0371 7.0757 0.5279 6.5478 2.5185 3.7370 2.5185 0.1985 2.7724 0.3541

-349.05 6.3750 1.3279 5.0471 7.2001 0.6345 6.5656 2.5235 3.8514 2.5235 0.1981 2.9411 0.4839

-349.05 6.3271 1.2838 5.0433 7.1511 0.5915 6.5595 2.5215 3.8054 2.5215 0.1982 2.8713 0.4446

-349.04 6.2909 1.2503 5.0406 7.1135 0.5589 6.5546 2.5203 3.7706 2.5203 0.1983 2.8205 0.4087

Table 7. The dipole moments µ (D), the polarizability α(a.u.), the average polarizability αo (esu), the anisotropy of the polarizability Δα (esu), and the first hyperpolarizability β(esu) of α-Methylstyrene

Parameter αxx αxy αyy αxz αyz αzz αtot Δα μx μy μz μ

a.u. -50.10 0.7615 -50.552 -0.1765 0.7356 -5.959 142.11 206.57 -0.0076 -0.03256 0.1347 0.3525

Parameter βxxx βxxy βxyy βyyy βxxz βxyz βyyz βxzz βyzz βzzz βtot

a.u. 5.529 -0.8695 3.2751 0.0432 0.8344 3.748 -2.0597 -2.6917 -1.1847 2.3028 48.9211

Graphical Abstract

In the present systematic work, the FT-IR, FT-Raman and 13C 1H NMR spectra of the αMethylstyrene were recorded. The observed fundamental frequencies in finger print and functional group regions were assigned according to their uniqueness region. The Gaussian computational calculations are carried out by HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6311++G(d,p) basis sets and the corresponding results were tabulated. The impact of the presence of vinyl group in phenyl structure of the compound is investigated. The modified vibrational pattern of the molecule associated vinyl group was analyzed. Moreover, 13C NMR and 1H NMR were calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP methods and the 6311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation between the base and ligand.

Highlights ► The Gaussian computational calculations are carried out for α-Methylstyrene. ► The NLO, optical properties, ESP, ED and the MEP were analyzed. ► The UV-Visible spectra indicate that, the electronic transitions shifted bathochromically. ► It is also found that the present compound is optical and bio active and has NLO properties.