A study of the molecular, vibrational, electronic and quantum chemical investigation of 2-methyl-1-vinylimidazole

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 1569–1581

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A study of the molecular, vibrational, electronic and quantum chemical investigation of 2-methyl-1-vinylimidazole R. John Xavier ⇑, P. Dinesh Department of Physics, Periyar EVR College (Autonomous), Tiruchirappalli 620 023, India

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

 The FT-IR and FT-Raman spectra of

The spectroscopic properties of the title compound 2-methyl-1-vinylimidazole (2M1VIM) led to the complete FT-IR and FT-Raman vibrational studies, calculation of HOMO–LUMO, NBO analysis and molecular electrostatic potential (2M1VIM). The temperature dependence of thermodynamic properties has been analysed. The values of the total dipole moment (l) and the first order hyperpolarizability (b) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The 13C and 1H nuclear magnetic resonance (NMR) chemical shifts of the molecule have been recorded.

1-methyl-2-imidazolethiol have been recorded.  The temperature dependence of the thermodynamic properties was investigated.  The atomic charges and charge delocalization of the molecule have been analysed.  The reactivity sites have been identified by MESP analysis.  NMR spectra have been investigated.

a r t i c l e

i n f o

Article history: Received 14 August 2014 Received in revised form 1 October 2014 Accepted 15 October 2014 Available online 24 October 2014 Keywords: 1-Methyl-2-imidazolethiol FT-IR FT-Raman NMR:DFT SQM

a b s t r a c t The spectroscopic properties of 2-methyl-1-vinylimidazole (abbreviated as 2M1VIM) were examined by FT-IR, FT-Raman and NMR techniques. FT-IR and FT-Raman spectra were recorded in the region 4000–400 cm1 and 3500–50 cm1, respectively. The 1H and 13C NMR spectra were recorded in CDCl3. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional theory (DFT) employing B3LYP and LSDA methods with 6-311++G(d,p) basis set. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibration were assigned on the basis of potential energy distribution (PED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method. The optimized structure of the compound was interpreted and compared with the reported experimental values. The observed vibrational ware numbers, absorption wavelengths and chemical shifts were compared with calculated values. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. As a result, the optimized geometry, and calculated spectroscopic data show a good agreement with the experimental results. Ó 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 431 2780286. E-mail address: [email protected] (R. John Xavier). http://dx.doi.org/10.1016/j.saa.2014.10.050 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

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Introduction Vinylimidazoles are an important class of heterocyclic compounds and their biological activities have been investigated extensively [1–3]. Imidazole containing macromolecules have been suggested as carrying an active moiety of several electrolytic enzymes. Imidazole is an excellent electron donor (D), imidazoles also act as building block of many biologically relevant molecules and present in histidine, which plays a vital part in the structure and binding functions of hemoglobin. In nature, the imidazole ring of histidine is reversibly protonated and deprotonated on alteration of the tyrosine redox state. It can strongly interact with a variety of electron acceptors and a form charge transfer complexes with them. Imidazole and its derivatives are widely used as intermediates in synthesis of organic compounds including pharmaceuticals, agrochemicals, dyes, photographic chemicals, corrosion inhibitors, epoxy curing agents, adhesives and plastic modifiers [4,5]. The imidazole ring is present in most proteins (i.e. histamine, histidine, etc.,) and is responsible for their catalytic activity. Consequently, extensive studies of the catalytic behaviours of monomeric [6] and polymeric [7] imidazole have been reported. Poly N-vinylimidazole copolymer coatings has been shown to have good corrosion protection and adhesion promotion capabilities for copper substrate in severe environments [8,9]. Several theoretical investigations have been devoted to imidazoles covering their geometry, energetics, tautomer equilibrium and protonation enthalpies [10–20] involving ab initio [10,11,13,15–18], DFT [11,13] and semi empirical methods [10,12,13,15,20,21]. However, the structure and vibrational assignments using ab initio/DFT calculations have not been investigated for 2-methyl-1-vinylimidazole (2M1VIM). Therefore, in the present study FT-IR spectral measurement and DFT electronic structure calculations of 2M1VIM have been undertaken to provide a detailed spectroscopic and electronic structure properties. Experimental details The compound 2-methyl-1-vinylimidazole in liquid state with a stated purity of 99% was purchased and it was used as such without further purification. The mid infrared spectrum of the compound was recorded between 4000 and 400 cm1 on a BRUKER IFS 66V model FT-IR Spectrophotometer. A KBr beam splitter and liquid nitrogen cooled MCT detector were used to collect the mid-infrared spectra. The FT-Raman spectra of 2M1VIM were recorded on a computer interfaced BRUKER IFS 66V model interferometer equipped with FRA-106 FT-Raman accessories. The spectra were recorded in Stokes region 3500–50 cm1 using ND:YAG laser operating at 200 mW power continuously with 1064 nm excitation. The reported wavenumbers are expected to be accurate within ±1 cm1. The spectral resolution is 2 cm1. 1H and 13C nuclear magnetic resonance (NMR) (400 MHz; CDCl3) spectra were recorded on a BRUKER HC400 instrument. The chemical shifts for protons are reported in parts per million (ppm) scales (scale) downfield from tetramethylsilane. Computational details The combination of spectroscopic methods with DFT calculations are powerful tools for understanding the fundamental vibrations and the electronic structure of the compound. The density functional theory (DFT) algorithm was used in the calculation and all the calculations in this work were performed by using GAUSSIAN 09W software package [22]. The structural characteristics, stability, thermodynamic properties and energy of 2M1VIM are determined by DFT [23,24] with the Becke’s three-parameter

hybrid functional (B3) [25,26] for the exchange part and the Lee– Yang–Parr (LYP) correlational functional [27], using basis set 6311++G(d,p) augmented by ‘‘d’’ polarization functions on heavy atoms and ‘‘p’’ polarization function on hydrogen atoms were used [28,29]. Entire thermodynamic properties namely the SCF energy, total thermal energy, heat capacity at constant volume and entropy of 2M1VIM were calculated by B3LYP method using 6-311++G(d,p) basis set. The isotropic chemical shifts are frequently used as aid in identification of organic compounds and accurate predictions molecular geometrics are essential for reliable studies of magnetic properties. The 1H and 13C NMR isotropic shielding were calculated with the Gauge invariant atomic orbital (GIAO) method using the optimized parameters obtained from B3LYP/6-311++G(d,p) method. The effect of CDCl3 on the theoretical NMR parameters was included using integral equation formalism polarizable continuum model (IEFPCM) method. In IEFPCM, one divides the problem into a solute part lying inside a cavity, and a solvent part represented as structure less material, characterized by its dielectric constant as well as other macroscopic parameters. Additionally, the electronic properties such as HOMO and LUMO energy values and energy gap for 2M1VIM were calculated by using B3LYP method 6-311++G(d,p) basis set. Furthermore, molecular electrostatic potentials (MEPs) of 2M1VIM were plotted in 3D by using optimized structures at B3LYP/6-311++G(d,p) level. Natural charges were determined by NBO analysis of with B3LYP/ 6-311++G(d,p) method.

Results and discussion Structural parameters Before computing the frequencies and electronic properties, it is necessary to analyses the molecular structure of the studied molecule. So that the structure is optimized at DFT level of theory and atomic numbering scheme of the title compound is given in Fig. 1. The calculated structural parameters containing bond lengths and bond angles using B3LYP and LSDA methods with 6311++G(d,p) basis set are listed in Table 1 along with the available XRD for 2M1VIM. As shown in Table 1, the theoretical values of optimized parameters, it is found that most of the optimized bond lengths are slightly larger than the experimental values and the bond angles are also slightly different from the experimental one. Taking into account that the molecular geometry in the vapour phase may be different from in the solid phase, owing to extended hydrogen bonding and stacking interactions there is responsible agreement between the calculated and experimental geometric parameters. It is observed that the CAN (ring) bond distances calculated for 2M1VIM are well agreed with experimental values as 1.344, 1.379, 1.326, and 1.347 Å respectively. The CAC bonds for the title molecules are about equal to the experimental values. These bond lengths C4AC5 and C6AC8 were calculated 1.362, 1.364 and 1.331, 1.330 Å respectively at B3LYP and LSDA with 6-311++G(d,p) basis set respectively. Experimental values of CAC are 1.361 Å. The optimized CAH bond lengths were calculated at 1.08 Å and 1.09 Å, respectively, using B3LYP and LSDA methods respectively. This calculated bond lengths show very good correlation with structurally similar molecule [30]. The CANAC, NACAN, and NACAC bond angles are slightly higher than the experimental value. The determined structural parameters of the title compound well correlated with the X-ray data of imidazole derivative [30]. Although the theoretical configuration are not exactly close to the XRD values for the studied compound, they are generally

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Fig. 1. Molecular structure of 2-methyl-1-vinylimidazole along with numbering of atoms.

methods with 6-311++G(d,p) basis set and are presented in Table 2. The zero point energies, thermal correction to internal energy, enthalpy, Gibbs free energy and entropy as well as the heat capacity for molecular systems were also determined. Thus, all these molecules having zero dipole moment values in the molecular zaxis. The larger total dipole moment of 2M1VIM, (3.03 Debye) is due to the steric interaction between the methyl group and vinyl groups. The temperature dependence of thermodynamic properties entropy (S), heat capacity at constant pressure (Cp) and enthalpy change (DH0 ? T) were also determined by B3LYP and LSDA methods with 6-311++G(d,p) basis set and are listed in Table 3. The anharmonicity effects have been eliminated by scaling the thermodynamic properties by 0.99 for 2M1VIM. Figs. 2–4 depicts the correlation of heat capacity at constant pressure (Cp), entropy (S) and enthalpy charge (DH0 ? T) with temperature along with the correlation equations. Form Figs. 2–4 one can clearly observed that there is a significant difference in entropy, heat capacity and enthalpy changes were increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature [31]. The observed relation of the thermodynamic function vs temperatures has regression factors (R2) which are all not less than 0.9987. The corresponding relations between entropy, heat capacity and enthalpy with temperature for 2M1VIM are given below by B3LYP method.

C 0p;m ¼ 4:09869 þ 0:1069946T þ 0:27280899  105 T 2 ðR2 ¼ 0:99878Þ

accepted that the bond lengths and bond angles depend upon the method and the basis set used in the calculations. The optimized geometrics represent good approximations and can be used as foundations to calculate molecular parameters to clarify experimental phenomena and further to predict other properties.

S0m ¼ 2:01214 þ 0:107184T þ 50:13188  105 T 2

Temperature dependence of thermodynamic properties

DH0m ¼ 3:13654 þ 0:0103761T  0:8654572  105 T 2

ðR2 ¼ 0:99998Þ

ðR2 ¼ 0:99954Þ

The energies and calculated thermodynamic parameters of 2M1VIM have also been computed by employing B3LYP and LSDA

LSDA method

Table 1 Optimized geometrical parameters (bond lengths and bond angles) of 2-methyl-1-vinylimidazole.

a

Value

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

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

Experimental dataa

Bond length C1AN2 C1AN5 C1AC6 N2AC3 N2AC10 C3AC4 C3AH15 C4AN5 C4AH16 C6AH7 C6AH8 C6AH9 C10AH11 C10AC12 C12AH13 C12AH14

(Å) 1.389 1.311 1.493 1.391 1.403 1.363 1.076 1.381 1.079 1.095 1.089 1.095 1.082 1.333 1.081 1.082

1.378 1.309 1.471 1.375 1.385 1.363 1.086 1.367 1.089 1.103 1.098 1.103 1.094 1.330 1.090 1.092

1.344 1.379 1.464 1.326 – 1.347 1.361 1.374 – 1.418 0.998 – 1.354 1.302 1.224 –

Values taken from Ref. [36].

Value

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

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

Experimental dataa

Bond angle (°) N2AC1AN5 N2AC1AC6 N5AC1AC6 C1AN2AC3 C1AN2AC10 C3AN2AC10 N2AC3AC4 N2AC3AH15 C4AC3AH15 C3AC4AN5 C3AC4AH16 N5AC4AH16 C1AN5AC4 C1AC6AH7 C1AC6AH8 C1AC6AH9 H7AC6AH8 H7AC6AH9 H8AC6AH9 N2AC10AH11 N2AC10AC12 H11AC10AC12 C10AC12AH13 C10AC12AH14 H13AC12AH14

106.10 131.61 122.29 110.88 125.30 123.82 106.59 110.29 121.50 128.21 106.14 121.31 132.56 111.46 128.94 119.60 124.31 118.41 117.28 107.52 112.11 112.01 108.31 108.75 108.04

106.53 130.74 122.73 110.64 124.95 124.41 106.62 110.29 121.68 128.04 105.92 121.12 132.96 111.67 128.33 120.00 123.69 118.57 117.74 107.22 112.35 112.35 108.52 108.52 107.77

104.5 125.4 113.5 – 130.1 107.1 125.6 – – – 104.7 – – 110.3 – 127.3 118.6 117.4 – – – – 124.0 – –

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Table 2 Theoretically computed thermodynamic parameters of 2-methyl-1-vinylimidazole calculated at B3LYP and LSDA with the basic set 6-311++G(d,p) method. Parameter

2-Methyl-1-vinylimidazole B3LYP 6311++G(d,p)

LSDA 6311++G(d,p)

343.02423 82.29656 3.63584 2.02331 1.31221

341.12550 80.46299 3.73207 2.06039 1.33877

86.446 0.889 0.889 84.668

85.214 0.889 0.889 83.437

Molar capacity at constant volume (calmol1 Kelvin1) Total 25.772 Translational 2.981 Rotational 2.981 Vibrational 19.810

28.386 2.981 2.981 22.425

Entropy (calmol1 Kelvin1) Total Translational Rotational Vibrational

80.203 39.949 27.901 12.353

86.312 39.949 27.837 18.526

2.6524 1.4823 0.0902 3.0398

2.5946 1.5361 0.0000 3.0152

SCF energy (Hartrees) Zero-point vibrational Energy (kJ/mol) Rotational constants (GHz)

Thermal energy (kJ/mol) Total Translational Rotational Vibrational

(electron + nuclei) distribution, molecular shape. Size and dipole moments of the molecule and it provides a visual method to understand the relative polarity of the compound [32]. Electrostatic potential (ESP) maps illustrate the charge distribution of molecule three dimensionally knowledge of the charge distribution can be used to determine how molecule interact with one another. Ultimate purpose of finding ESP is to find the reactive site of a molecule [33,34]. These maps allow as visualizing the different polar regions of a molecule. The total electron density and MESP surfaces of the molecule are constructed by using B3LYP/6311++G(d,p) method. These pictures illustrate an electrostatic

Dipole moment (Debye)

lx ly lz ltotal

Fig. 2. Correlation graphic of entropy and vinylimidazole.

temperature for 2-methyl-1-

C 0p;m ¼ 4:40004 þ 0:11092480T þ 1:896933771  105 T 2 ðR2 ¼ 0:99892Þ S0m ¼ 2:61359 þ 0:11976315T þ 52:899331  105 T 2 ðR2 ¼ 0:99997Þ

DH0m ¼ 3:16015 þ 0:01283903T  0:994062544  105 T 2 ðR2 ¼ 0:99953Þ

Analysis of frontier molecular orbitals (FMOS) and molecular electrostatic potential (MESP) The molecular electrostatic potential surface (MESP) which is mapping electrostatic potential onto the iso-electron density surface simultaneously displays electrostatic potential

Fig. 3. Correlation graphic of heat capacity and temperature for 2-methyl-1vinylimidazole.

Table 3 Thermodynamic properties at different temperatures at the DFT/B3LYP and LSDA with the basic set 6-311++G(d,p) level for 2-methyl-1-vinylimidazole. T (K)

100 200 298.15 300 400 500 600 700 800 900 1000

Entropy S (J mol–1 K–1)

Heat capacity Cp (J mol–1 K–1)

Enthalpy DH0 ? T (kJ mol–1)

B3LYP

LSDA

B3LYP

LSDA

B3LYP

LSDA

60.61185 70.99426 80.22945 80.40153 89.64149 98.64006 107.2514 115.3991 123.076 130.3059 137.1176

64.3499 76.13528 86.33843 86.52725 96.55354 106.1879 115.3179 123.9006 131.9503 139.4981 146.5918

11.77581 19.20889 27.75813 27.92543 36.59656 44.11568 50.30593 55.38002 59.58891 63.13098 66.14245

13.67352 21.4412 30.37285 30.54493 39.41683 46.98136 53.14771 58.174 62.33509 65.82935 68.79541

0.903442 2.442639 4.741874 4.794455 8.025813 12.07218 16.80449 22.09608 27.85134 33.99379 40.46128

1.061185 2.805927 5.344168 5.39914 8.905354 13.23853 18.25526 23.82887 29.86138 36.2739 43.00908

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Fig. 4. Correlation graphic of enthalpy and temperature for 2-methyl-1vinylimidazole.

potential model of the compound, computed at the 0.002 au isodensity surface. The MESP mapped surface of the compounds and electrostatic potential contour map for positive and negative potentials are shown in Figs. 5–7. The colour scheme of MESP is the negative electrostatic potentials are shown in red, the intensity of which is proportional to the absolute value of the potential energy, and positive electrostatic potentials are shown in blue while green indicates surface areas where the potentials are close to zero. The colour-coded values are then projected onto the 0.002 au isodensity surface to produce a three-dimensional electrostatic potential model. Molecular orbitals, when viewed in a qualitative graphical representation, can provide insight into the nature of reactivity, and some of the structural and physical properties of the molecules. Molecular orbitals both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and their properties such as energy are very useful for physicists and chemists for better understanding of chemical reaction. The HOMO is the orbital that primarily acts as an electron donor, and the energy of the HOMO is directly related to the ionization potential. The LUMO is the orbital that largely acts as the acceptor, and the energy of the LUMO is directly related to electron affinity [32,35,36]. This is also used by the frontier electron density for predicting most reactive position in p-electron systems and also explains several types of reaction in conjugated system [37]. Surfaces for the frontier orbitals were drawn to understand the bonding scheme of present compound. The molecular orbitals are defined as Eigen function of the Fock operator, which exhibits the full symmetry of the nuclear point, they necessarily form a basis for irreducible representation of full point-group symmetry. The energies of HOMO, LUMO, LUMO + 1 and HOMO  1 and their orbital energy gaps calculated by B3LYP/6-311++G(d,p) method and the pictorial illustration of FMOs and their respective positive and negative regions are shown in Fig. 8. The positive and negative phase is represented in red and green colour respectively. The region of HOMO and LUMO levels spread over the entire molecule and the calculated energy gap of HOMO–LUMO explains the ultimate charge transfer interface within the molecule. The frontier orbital energy gap (EHOMO–ELUMO) in case of the title molecule is found to be 0.20114 eV. GAUSS VIEW 5.0.8 visualization program [38] has been utilized to construct the MESP surface, the shapes of all the molecular orbitals.

Mulliken atomic charge The computation of the reactive atomic charges plays an important role in the application of quantum mechanical calculation for the molecular system [38] because atomic charges affect dipole moment, polarizability electronic structure and much more

Fig. 5. Molecular electrostatic potential map of 2-methyl-1-vinylimidazole.

Fig. 6. The total electron density surface of 2-methyl-1-vinylimidazole.

properties of molecular system. The Mulliken atomic charges of 2M1VIM are computed by the DFT/B3LYP method with 6-311++G(d,p) basis set, and are presented in Table 4. Mulliken population analysis chart of 2M1VIM is shown in Fig. 9. From Table 4, it is clear that the substitution of methyl and vinyl group in the imidazole ring leads to the redistribution of electron density. The N1 atom has the positive value. The negative values on C2 and C4 atom in the imidazole ring lead to the redistribution of electron density. C5 atom accommodates positive charge and becomes more acidic. Hydrogen atoms exhibit a positive charge, which is an acceptor atom for the title molecule. Natural bond orbital (NBO) analysis The atomic charges of 2M1VIM calculated by NBO analysis using the B3LYP/6-311++G(d,p) method are presented in Table 5.

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the strong electronegative nature of nitrogen mashed the ACH3 effect and hence the C2 has positive charge. The significant variation of the charges of atoms in the tile compound is due to the substitution of ACH3 and vinyl group at different positions. Donor acceptor interactions: perturbation theory energy analysis NBO calculation is done by examining all possible interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’ (acceptor) non-Lewis NBOs and estimating their energetic importance by 2nd order perturbation theory. Strong electron delocalization in the Lewis structure also shows up as donor–acceptor interactions. The stabilization of orbital interaction is proportional to the energy difference between interacting orbitals. Therefore, the interaction having strongest stabilization takes place between effective donors and effective acceptors. This bonding-anti bonding interaction can be quantitatively described in terms of the NBO approach that is expressed by means of second-order perturbation interaction energy E(2) [39–41]. This energy represents the estimate of the off-diagonal NBO Fock matrix element. The stabilization energy E(2) associated with i (donor) ? j (acceptor) delocalization is estimated from the second-order perturbation approach [39] as given below

Eð2Þ ¼ qi Fig. 7. Electrostatic potential surface of 2-methyl-1-vinylimidazole.

In 2M1VIM, the carbon atoms (C2, C4 and C5) in the vinyl imidazole ring the atom C2 is positively charged while the atoms C4 and C5 are negatively charged. Especially the carbon atom C2 attached with ACH3 group is positively charged. Even though ACH3 group is positively charged, even though ACH3 is electron donating group

F 2 ði; jÞ ej  ei

where qi is the donor orbital occupancy, ei and ej are diagonal elements (orbital energies) and F(i, j) is the off-diagonal Fock matrix element. The second order perturbation analysis of Fock matrix of 2M1VIM are summarised in Table 6. The Fock matrix analysis yields different types of donor–acceptor interactions and their stabilization energies. As seen from Table 6 shows calculated natural

HOMO -1 = -0.25736

LUMO +1 = -0.01048

HOMO = -0.23386

LUMO = -0.03272

Fig. 8. Surfaces of FMOs for 2-methyl-1-vinylimidazole (orbital numbers are extracted from the output results of the B3LYP calculation).

R. John Xavier, P. Dinesh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 1569–1581 Table 4 Mulliken atomic charges of 2-methyl-1-vinylimidazole using B3LYP method with 6-311++G(d,p). Atoms

B3LYP

N1 C2 N3 C4 C5 C6 H7 C8 H9 H10 C11 H12 H13 H14 H15 H16

0.10020 0.01870 0.09862 0.11009 0.01670 0.04773 0.14724 0.43103 0.11954 0.15821 0.76867 0.18640 0.16118 0.16456 0.17687 0.14845

Fig. 9. Plot of Mulliken charges of 2-methyl-1-vinylimidazole.

Table 5 Calculated atomic charges of charge 2-methyl-1-vinylimidazole by natural bond orbital (NBO) analysis. Atoms

2-Methyl-1-vinylimidazole B3LYP 6-311++G(d,p)

N1 C2 N3 C4 C5 C6 H7 C8 H9 H10 C11 H12 H13 H14 H15 H16

0.501 0.44365 0.5052 0.05332 0.05511 0.00545 0.1853 0.37897 0.19364 0.1965 0.60757 0.23027 0.21327 0.21916 0.20441 0.20952

orbital occupancy (number of electron (or) ‘‘natural population’’ of the orbital). It is noted that the maximum occupancies 1.99335, 1.98887, 1.98828, 1.98617 are obtained for BD (H10AH12), BD (N3AC4), BD (N1AC6), BD (N3AH15) respectively, and corresponding sp composition are also tabulated. Therefore, the results suggest that the H10AH12, C6AH7 bond lengths of this compound

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are essentially controlled by the p character of these hybrid orbitals and also by the nature the H10AH12. Delocalization of the electron density between occupied Lewis type (bond (or) lone pair) NBO orbital’s and formally unoccupied anti-bond (or) Rydberg) non Lewis NBO orbital’s corresponding to a stabilizing donor–acceptor interaction have been performed at B3LYP/6-31+G(d,p) basis set. The energy of these interactions can be estimated by the second order perturbation theory [42]. NMR spectra and calculations The isotropic chemical shifts are frequently used as an aid in identification of reactive organic as well as ionic species. It is recognized that accurate predictions of molecular geometries are essential for reliable calculations of magnetic properties. Therefore, full geometry optimization of 2M1VIM was performed by using B3LYP/6-311++G(d,p) method in CDCl3 solvents. Then, Gaugeincluding atomic orbital (GIAO) 1H and 13C chemical shift calculations of the compound have been made by same method. Application of the GIAO [43] approach to molecular systems was significantly improved by an efficient application of the method to the ab initio SCF calculations, using techniques borrowed from analytic derivative methodologies. GIAO procedure is somewhat superior since it exhibits a faster convergence of the calculated properties upon extension of the basis set used. Taking into account the computational cost and the effectiveness of calculation, the GIAO method seems to be preferable from many aspects at the present state of this subject. On the other hand, the density functional methodologies offer an effective alternative to the conventional correlated methods, due to their significantly lower computational cost. The 1H and 13C chemical shifts were measured in a less polar (CDCl3) and DMSO solvents. The result in Table 7 shows that the range 13C NMR chemical shift of the typical organic molecule usually is >100 [44,45], the accuracy ensures reliable interpretation of spectroscopic parameters. It is true from the above literature value, in our present study, the title molecule 2M1VIM also falls with the above literature data. The signals of the aromatic proton were observed at 25.58–25.09 ppm. The H atom is the smallest of all atoms and mostly localized on the periphery of molecules. Therefore their chemical shifts would be more susceptible to intermolecular interactions in the aqueous solution as compared to that for other heavier atoms. Another important aspect is that, hydrogen attached or nearby electron withdrawing atom or group can decrease the shielding and move the resonance of attached proton towards to a higher frequency. By contrast electron donating atom or group increases the shielding and moves the resonance towards to a lower frequency. The calculated chemical shifts have been compared with the literature data [46]. As seen from Table 7, the calculated chemical shifts in CDCl3 solvent have quite agreement with experimental data as mentioned in the above cited literature when compared with DMSO solvent chemical shifts. The corresponding NMR charges and NMR shielding surfaces are shown in Figs. 10 and 11, respectively. Polarizability and hyperpolarizability The values of the polarizability tensor components for a given system will depend on the choice of the Cartesian co-ordinate system used. The molecule for which axx = ayy = azz is said to be isotropic. The polarizability is isotropic or is the same in all directions for a molecule whose electron density is spherically symmetrical. If the molecules are perfectly isotropic (p) and (E) will have the same direction and is then a simple scalar quantity. If the molecule is anisotropic axx – ayy – azz, (p) will no longer have the same direction as (E). The intensity of Raman scattering may be proportional to the derived polarizability components. To express the scattering

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Table 6 NBO results showing the formation of Lewis and non Lewis orbital’s by valence hybrids corresponding to the intermolecular C–H  N hydrogen bonding. S. no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Bond AAB

ED/energy (a.u.)

BD(N1AC2) BD⁄(N1AC2) BD(N1AC5) BD⁄(N1AC5) BD⁄(N1AC5) BD⁄(N1AC5) BD(N1AC6) BD⁄(N1AC6) BD(C2AN3) BD⁄(C2AN3) BD(C2AH10) BD⁄(C2AH10) BD(N3AC4) BD⁄(N3AC4) BD⁄(N3AC4) BD⁄(N3AC4) BD(N3AH15) BD⁄(N3AH15) BD(C4AC5) BD⁄(C4AC5) BD(C4AH16) BD⁄(C4AH16) BD(C6AH7) BD⁄(C6AH7) BD(C6AC8) BD⁄(C6AC8) BD(C6AH9) BD⁄(C6AH9) BD(H10AC11) BD⁄(H10AC11) BD(H10AH12) BD⁄(H10AH12) BD⁄(H10AH12) BD⁄(H10AH12) BD(H12AH13) BD⁄(H12AH13) BD(H12AH14) BD⁄(H12AH14)

1.98321 0.04629 1.98400 0.04075 1.88006 0.16177 1.98828 0.01779 1.97303 0.02147 1.95652 0.03003 1.98887 0.01586 1.94917 0.15787 1.98617 0.01353 1.97437 0.01274 1.98224 0.01493 1.97452 0.00333 1.97738 0.00406 1.96767 0.00857 1.98114 0.01517 1.99335 0.09502 1.98736 0.00726 1.98000 0.00496 1.98202 0.00778

EDA (%) 37.06 62.94 41.07 58.93 38.75 61.25 50.93 49.07 63.12 36.88 63.20 36.80 50.20 49.80 52.78 47.22 60.46 39.54 41.33 58.67 60.74 39.26 61.27 38.73 61.67 38.33 61.22 38.78 59.97 40.03 48.33 51.67 50.99 49.01 59.87 40.13 59.52 40.48

EDB (%) 62.94 37.06 58.93 41.07 61.25 38.75 49.07 50.93 36.88 63.12 36.80 63.20 49.80 50.20 47.22 52.78 39.54 60.46 58.67 41.33 39.26 60.74 38.73 61.27 38.33 61.67 38.78 38.78 40.03 59.97 51.67 48.33 49.01 50.99 40.13 59.87 40.48 59.52

Table 7 Theoretical and experimental 13C and 1H isotopic chemical shifts of 2-methyl-1vinylimidazole using B3LYP/6-311++G(d,p) basis set. Assignment

Expt (diso)

dcal in DMSO

dcal in CDCl3

13.19 26.56 128.77 101.38 23.98 115.09

11.85 34.67 37.53 28.91 59.04 167.49

11.93 25.49 37.46 27.98 59.35 166.38

34.54 38.32 33.94 14.56 34.09 18.02 7.20 9.19

25.24 26.28 26.50 29.97 30.07 30.75 24.58 24.69

26.88 25.87 26.04 28.94 29.45 30.22 25.09 24.56

1

H H7 H9 H10 H12 H13 H14 H15 H16

2.49

2.62

0.6088(sp ) + 0.7933(sp ) 0.7933(sp2.49) + 0.6088(sp2.62) 2.31 0.6408(sp ) + 0.7677(sp2.31) 0.7677(sp2.31) + 0.6408(sp2.31) 0.6225(sp95.35) + 0.7826(sp99.66) 0.7826(sp95.35) + 0.6225(sp99.66) 0.7136(sp1.50) + 0.7005(sp2.74) 0.7005(sp1.50) + 0.7136(sp2.74) 0.7945(sp2.78) + 0.6073(sp2.80) 0.6073(sp2.78) + 0.7945(sp2.80) 0.7950(sp2.52) + 0.6067(sp2.69) 0.6067(sp2.52) + 0.7950(sp2.69) 0.7085(sp1.65) + 0.7057(sp1.74) 0.7057(sp1.65) + 0.7085(sp1.74) 0.7265(sp99.99) + 0.6871(sp99.99) 0.6871(sp99.99) + 0.7265(sp99.99) 0.7776(sp1.85) + 0.6288(sp0.00) 0.6288(sp1.85) + 0.7776(sp0.00) 0.6429(sp2.64) + 0.7660(sp2.43) 0.7660(sp2.64) + 0.6429(sp2.43) 0.7794(sp1.79) + 0.6265(sp0.00) 0.6265(sp1.79) + 0.7794(sp0.00) 0.7828(sp3.07) + 0.6223(sp0.00) 0.6223(sp3.07) + 0.7828(sp0.00) 0.7853(sp2.99) + 0.6191(sp0.00) 0.6191(sp2.99) + 0.7853(sp0.00) 0.7825(sp3.22) + 0.6227(sp0.00) 0.6227(sp3.22) + 0.7825(sp0.00) 0.7744(sp2.10) + 0.6327(sp0.00) 0.6327(sp2.10) + 0.7744(sp0.00) 0.6952(sp99.99) + 0.7188(sp99.99) 0.7188(sp99.99) + 0.6952(sp99.99) 0.7141(sp1.48) + 0.7001(sp1.64) 0.7001(sp1.48) + 0.7141(sp1.64) 0.7738(sp2.23) + 0.6335(sp0.00) 0.6335(sp2.23) + 0.7738(sp0.00) 0.7715(sp2.24) + 0.6362(sp0.00) 0.6362(sp2.24) + 0.7715(sp0.00)

S (%)

P (%)

28.63, 27.59 28.63, 27.59 30.20, 30.21 30.20, 30.21 1.04, 0.19 1.04, 0.19 40.03, 26.69 40.03, 26.69 26.41, 26.30 26.41, 26.30 28.42, 27.06 28.42, 27.06 37.66, 36.46 37.66, 36.46 0.85, 0.26 0.85, 0.26 35.12, 99.95 35.12, 99.95 27.44, 29.10 27.44, 29.10 35.77, 99.95 35.77, 99.95 24.57, 99.97 24.57, 99.97 25.08, 99.97 25.08, 99.97 23.68, 99.97 23.68, 99.97 32.26, 67.69 32.26, 67.69 0.56, 0.43 0.56, 0.43 40.24, 37.92 40.24, 37.92 30.96, 99.95 30.96, 99.95 30.80, 99.95 30.80, 99.95

71.20, 71.20, 69.66, 69.66, 98.80, 98.80, 59.93, 59.93, 73.53, 73.53, 71.52, 71.52, 62.30, 62.30, 99.08, 99.08, 64.84, 64.84, 72.41, 72.41, 64.19, 64.19, 99.97, 99.97, 74.86, 74.86, 76.26, 76.26, 99.95, 99.95, 99.37, 99.37, 37.92, 37.92, 68.99, 68.99, 69.15, 69.15,

72.34 72.34 69.70 69.70 99.66 99.66 73.25 73.25 73.57 73.57 72.81 72.81 63.49 63.49 99.65 99.65 0.05 0.05 70.81 70.81 0.05 0.05 0.03 0.03 0.03 0.03 0.03 0.03 0.05 0.05 99.50 99.50 62.03 62.03 0.05 0.05 0.05 0.05

moment using B3LYP/6-311++G(d,p) are presented in Table 8. The definitions [47] for the isotropic polarizability is

 Þ ¼ 1=3ðaxx þ ayy þ azz Þ ða

2-Methyl-1-vinylimidazole

13

C C2 C4 C5 C6 C8 C11

NBO

intensity in terms of the derived polarizability tensor, the quanti Þ and the anisotropy invariant (c) are necessary. They are ties ða constant regardless of the orientation of the molecules. The quan Þ is the mean value of the three principle components of ða Þ tity ða and (c) measures the anisotropy of the tensor. The polarizability, the first hyperpolarizability and the anisotropy polarizability invariant are computed with the numerical derivative of the dipole

The polarizability anisotropy invariant is

c2 ¼ 1=2½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6ða2xy þ a2yz þ a2zx Þ and the average hyperpolarizability is

btotal ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðb2x þ b2y þ b2z Þ

where axx, ayy and azz are tensor components of polarizability. bx, by and bz are tensor components of hyperpolarizability. Vibrational spectral analysis 2M1VIM belongs to Cs point group symmetry with 16 atoms and have 42 fundamental modes of vibration. From the group theory analysis for molecules of Cs symmetry the 42 fundamental vibrations are distributed among the symmetry species as Uvib = 28A0 + 14A00 , with A0 representing in-plane motions and A00 representing out-of-plane motions. All the vibrations are active in both IR and Raman. Normal coordinate analysis was carried out to provide a complete assignment of the fundamental vibrational frequencies for the molecules. For this purpose, the full set of 53 standard internal coordinates (containing 11 redundancies) was defined as given in Table 9. From these, a non-redundant set of local symmetry coordinates was constructed by suitable linear

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Table 8 Electric dipole moment, polarizability and hyperpolarizability of 2-methyl-1-vinylimidazole by DFT/B3LYP with the basic set 6-311++G(d,p). Parameters

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

LSDA

axx ayy azz axy axz ayz aTotal  1025

48.981 43.3822 51.8268 4.0142 0.0077 0.3917 48.981

48.39 43.1824 51.9594 4.0539 0.0001 0.0002 48.39

Anisotropic tensor A B C

110.756408 16.2672898 104.180074

116.895443 16.4341053 107.750037

Hyper polarizability (b) bxxx byyy bzzz bxyy byxx bzxx bxzz byzz bzyy bx by bz bTotal  1030 cm5 esu1

8.5067 6.7908 0.2106 6.8866 12.3398 0.3857 0.2568 3.4822 0.9494 15.1365 15.6484 0.7743 4.088

7.234 7.6877 0.0001 7.3705 12.4891 0.0004 0.3461 3.4357 0.0005 14.2584 16.7411 0.0002 4.165

Polarizability (a)

Fig. 10. 1H NMR experimental spectrum of 2-methyl-1-vinylimidazole.

Fig. 11.

13

C NMR experimental spectrum of 2-methyl-1-vinylimidazole.

combinations of internal coordinates following the recommendations of Pulay et al. [48] and were presented in Table 10. The goal of the vibrational analysis is to find vibrational modes connected with molecular structure of investigated compound. The numerical harmonic vibrational analysis was done for the optimized geometry; the absence of negative frequencies for the stationary point’s ground at the molecular potential. The goal of the vibrational analysis is to find vibrational modes connected with molecular structure of investigated compound. The numerical harmonic vibrational analysis was done for the optimized geometry, the absence of negative frequencies for the stationary points found at the molecular potential energy hyper surfaces confirming that this structure correspond to real minimum. Vibrational spectral assignments were performed on the recorded FT-IR and FT-Raman spectra based on theoretically predicted wavenumbers and their TED. The observed and calculated wavenumbers along with their relative intensities, scattering activities, and probable assignments with TED of compound are given in Table 11. It should be noted that the calculations were made for a free molecule in vacuum, while the experiment was performed for the solid sample. Furthermore, the anharmonicity is neglected in the real system for the calculated vibrations. Therefore, there are disagreements between the calculated and observed vibrational wavenumbers, and because of the low IR intensities of some modes, it is difficult to observe them in the IR spectrum. In order to improve the agreement of theoretically calculated frequencies with experimentally calculated frequencies, it is necessary to scale down the theoretically calculated harmonic frequencies. Hence,

the vibrational frequencies theoretically calculated at B3LYP/ 6-311++G(d,p) are scaled down by using MOLVIB 7.0 version written by Sundius [49,50]. The combined FTIR and FT-Raman spectrum of the title compound under investigation are shown in Figs. 12 and 13. The observed and calculated frequencies using B3LYP and LSDA method using 6-311++G(d,p) along with their relative intensities, probable assignments and potential energy distribution (PED) of 2M1VIM are summarised in Table 11 respectively. CAH vibrations The wave numbers in the high wave-number region of the vibrational spectra are systematically higher than their corresponding counter parts. Such differences are usually observed for XAH vibrations (X = C, N). Moreover, the substitution group does not appear to affect the position of characteristic CAH bands and these bands occur in the range 3100–3000 cm1. The bands appeared at 3118 cm1 in FT-Raman spectrum and 3110, 3041 cm1 in FT-IR spectrum of 2M1VIM have been assigned to CAH stretching vibrations, respectively, as show in Table 11. The assigned values of CAH showed good agreement with the available literature data [51,52]. The CAH in-plane and out-plane vibrational frequencies are found to be well within their characteristic region. CH2 group vibrations The molecule under investigation possesses only one CH2 group and hence expects one symmetric and one asymmetric CAH stretching vibrations in CH2 group. The group of bands between 2990 and 2925 cm1 can be clearly assigned to the antisymmetric and symmetric modes of these groups as indicated in Table 11. The scissoring mode is assigned, in agreement with heterocyclic compounds containing the imidazole ring [53] at 1501 and

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Table 9 Definition of internal coordinates of 2-methyl-1-vinylimidazole. No

Symbol

Type

Definition

Stretching 1–5 6–8 9–11 12–14 15–16

ri Ri Ei Ni mi

CAN CAC CAH CAH (methyl) CAH (methylene)

C2AN1, C5AN1, C2AN3, C4AN3, C6AN1 C2AC4, C4AC5, C6AC8 C4AH15, C5AH16, C6AH7 C11AH12, C11AH13, C11AH14 C8AH9, C8AH10

bi

/i

Ring CNC NCC NCH CCH NCH NCC CCH HCH CCH HCH

N1AC2AN3, C2AN3AC4, N3AC4AC5, C4AC5AN1, C5AN1AN2 C2AN1AC6, C5AN1AC6 N1AC2AC11, N3AC2AC11 N1AC5AH16, N3AC4AH15 C4AC5AH16, C5AC4AH15 N1AC6AH7 N1AC6AN1 C2AC11AH12, C2AC11AH13, C2AC11AH14 H12AC11AH13, H12AC11AH14, H13AC11AH14 C6AC8AH9, C6AC8AH10 H9AC8AH10

xi xi xi xi

CC CN CH CC

C11AC2AN1AN3 C6AN1AC2AC5 H15AC4AN3AC5, H16AC5AC4AN1, H7AC6AN1A(C2, C5) C8AC6AN1A(C2, C5)

si si si

sRing sCH2 sCH3

N1AC2AN3AC4, C2AN3AC4AC5, N3AC4AC5AN1, C4AC5AN1AC2, C5AN1AC2AN3 ((H9, H10)AC8AC6AN1 (H12, H13, H14)AC11AC2A(N1, N3)

Bending 17–21 22–23 24–25 26–27 28–29 30 31 32–34 35–37 38–39 40 Out-of-plane bending 41 42 43–45 46 Torsion 47–51 52 53

ai ci ri ri ri gi ei Ri

wi

For numbering of atoms refer Fig. 1.

1500 cm1 in FTIR and FT-Raman spectrum, respectively. As predicted by the calculation, the band at 1367 cm1 is easily assigned to the wagging mode, while the expected rocking mode are assigned according to the PED contribution to the band at 1038 cm1 in both FTIR and FT-Raman, respectively. The twisting mode of the title compared is observed at 1291 cm1 in FT-Raman spectrum. CH3 group vibrations For the assignments of CH3 group frequencies, basically nine fundamentals can be associated to each CH3 group namely, CH3ss – symmetric stretch, CH3ips – in-plane stretch (ie, in-plane hydrogen stretching modes); CH3sb – symmetric bending; CH3ipr – inplane rocking; CH3opr – out of plane rocking; CH3ops – out of plane stretch; CH3opb – out of plane bending modes and tCH3 – twisting modes. The CH3ips frequency in the Raman spectrum is established at 2957 cm1 in 2M1VIM. The symmetric stretching CH3ss is observed at 2927 and 2928 cm1 in the FTIR and FT Raman respectively. The CH3ipb deformational mode is obtained at 1462 cm1 in FT Raman spectrum. The IR and Raman bands at 1380 and 1379 cm1, respectively of 2M1VIM are assigned to CH3ops, out-of-plane stretching is observed at 2868 cm1 in FTIR spectrum of 2M1VIM. The CH3opb, out-of-plane bending frequencies are established at 1158 and 1157 cm1 in FTIR and FT Raman spectrum respectively for the title molecule. The CH3 in-plane and out-of-plane rocking modes and CH3 twisting modes are identified and assigned. These assignments were show good agreement with the calculated values and also supported by the literatures [54,55] in addition to PED output. Imidazole ring vibrations In 2M1VIM, the IR band observed at 1581 cm1 are assigned to C@N stretching. The CAN (ring) stretching vibrations of 2M1VIM are established at 1427, 1407, 1278 cm1 and 1428, 1406 and

1277 cm1 in FT-IR and FT-Raman spectrum, respectively. The C@C stretching band in the Raman spectrum appeared at 1572 cm1 in 2M1VIM. All other observed skeletal in-plane and

Table 10 Definition of local symmetry coordinates of 2-methyl-1-vinylimidazole. No

Symbola

Definitionb

1–5 6–8 9–11 12 13 14 15 16 17 18 19 20 21–23 24 25 26 27 28 29 30 31 32 33 34 35–37 38 39 40 41 42

CN CC CH CH3ss CH3ips CH3ops CH2ss CH2ass R bend 1 R bend 2 bCN bCC bCH bCC CH3sb CH3ipb CH3opb CH3ipr CH3opr CH2 twist CH2rock CH2sciss xCC xCN xCH xCC s Ring 1 s Ring 2 CH2wag sCH3

r1, r2, r3, r4, r5 R6, R7, R8 E9, E10, E11 p (N12 + N13 + N14)/ 3 p (2N12 + N13 + N14)/ 6 p (N13  N14)/ 2 p (V15 + V16)/ 2 p (V15  V16)/ 2 b17 + a(b18 + b21) + b(b19 + b20) (a  b) (b18  b21) + (1  a)(b19  b20) p (a22  a23)/ 2 p (c24  c25)/ 2 p p (r26  r28)/ 2, (r27  r29)/ 2, r30

g

31 p (e32  e33  e34 + e35 + e36 + e37)/ 6 p (e35  e36  e37)/ 6 p (e35  e36)/ 2 p (2e32  e33  e34)/ 6 p (e33  e36)/ 2 p (w38 + w39)/ 2 p (w38  w39)/ 2 p (2w40  w38  w39)/ 6

x41 x42 x43, x44, x45 x46 b(s47 + s51) + a(s48 + s50) + s49 (a  b) (s50  s48) + (1  a) (s51  s47) s52 s53

a = Cos 144°, b = Cos 72°. a The internal coordinates used her are defined in Table 9. b These symbols are used for description of normal modes by PED in Table 11.

Table 11 The observed (FTIR and FT-Raman) and calculated (unscaled and scaled) frequencies using B3LYP and LSDA/6-311++G(d,p) and B3LYP/6-311++G(d,p) along with their probable assignments and potential energy distribution of 2-methyl1-vinylimidazole. S. no

Species

Observed frequency (cm1)

Calculated frequencies (cm1)

Assignments along with PED (%)

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

A0 A0 A0 A0 A0 A0 A0 A00 A0 A0 A0 A0 A0 A0 A0 A0 A0 A00 A0 A0 A00 A0 A00 A0 A0 A0 A0 A00 A0 A0 A0 A0 A0 A00 A00 A00 A00 A00 A00 A00 A00 A00

FT-IR

FT-Raman

Unscaled

Scaled

IR intensity

Raman intensity

Unscaled

Scaled

IR intensity

Raman intensity

– 3110 3041 2999 2967 – 2927 2868 1699 1581 – 1531 1501 – 1427 1407 1380 1367 – – – 1278 1158 1128 1076 1038 984 – 961 880 –

3118 – – – – 2957 2928 – 1698 – 1572 1533 1500 1462 1428 1406 1379 – 1357 1351 1291 1277 1157 1129 1075 1038 983 966 – – 874 851 – – 662 624 – – – – – –

3271 3268 3240 3184 3172 3135 3075 3025 1701 1575 1533 1494 1484 1456 1440 1409 1365 1313 1271 1220 1168 1116 1062 1031 1001 998 918 889 865 731 712 704 669 665 613 500 353 262 251 249 178 18

3130 3119 3058 3009 2978 2967 2939 2878 1692 1578 1570 1521 1494 1460 1430 1408 1375 1356 1347 1348 1284 1270 1143 1119 1061 1020 980 954 950 869 863 841 721 664 656 620 591 266 256 247 180 23

1.67 0.54 3.23 1.35 1.97 1.87 0.48 2.57 16.76 18.13 2.66 2.11 36.06 5.29 54.63 0.53 18.58 20.99 4.34 1.40 18.30 14.29 20.10 8.15 99.65 4.56 3.21 117.72 17.64 9.60 7.72 64.11 6.70 139.22 19.10 13.44 4.81 2.89 3.78 4.04 1.85 3.26

3206.83 327.93 852.59 769.93 888.41 1585.44 873.14 180.51 122.88 12.68 779.70 672.03 47.84 82.54 372.96 217.61 108.18 105.10 7.39 15.99 262.66 326.53 100.70 67.27 352.97 734.95 100.54 379.37 1065.15 150.79 134.86 751.26 67.19 1605.33 376.08 122.15 132.92 62.96 252.20 168.00 197.18 77.51

3207 3196 3170 3114 3100 3082 3018 2957 1687 1571 1522 1443 1418 1399 1371 1345 1333 1287 1264 1231 1149 1070 1010 995 958 953 900 841 829 722 713 683 659 657 606 499 336 272 264 245 183 27

3122 3113 3046 3003 2970 2960 2931 2874 1685 1573 1566 1519 1489 1451 1419 1392 1366 1350 1333 1354 1279 1263 1145 1110 1054 1011 988 949 943 857 850 839 718 660 651 611 582 268 259 248 181 25

1.46 0.28 6.29 0.23 0.32 1.89 0.87 3.56 22.66 10.09 15.95 20.70 1.30 4.18 57.39 0.17 7.50 18.11 10.29 2.67 20.88 10.64 10.23 11.00 29.44 10.69 21.23 44.05 15.51 16.43 86.50 50.36 17.43 142.59 11.93 4.56 0.55 3.82 0.56 3.34 0.10 0.00

1536.75 212.06 604.17 1259.05 152.88 1850.96 1061.92 200.60 1.30 127.78 88.86 12.94 1334.26 59.66 269.87 183.09 125.68 45.71 16.60 8.91 279.42 92.14 172.39 94.20 244.14 416.16 567.79 78.54 165.37 28.70 1030.78 674.68 310.51 1694.22 492.95 147.24 146.85 74.76 290.64 193.58 239.11 93.63

731 666 – 624 604 519 – – – –

CH(100) CH(100) CH(100) CH2 ass(99) CH2ss(99) CH3ips(98) CH3ss(98) CH3ops(98) CC(96) CN(97) CC(96) Rbend1(81), bCC(13) CH2sciss(86) CH3ipb(89) CN(87), Rbend2(21) CN(86), bCN(19) CH3sb(89) CH2wag(87) CN(80) CC(79) CH2 twist(81) CN(79) CH3 opb(74) bCC(69) Rbend 2(67) CH2 rock(76) bCC(68) CH3opr(70) CH3ipr(78) bCN(66) bCH(62) bCH(59) bCH(62) xCC(57) sRing 2(59) xCN(57) xCC(53) xCH(54) sRng1(51) xCH(57) xCH(55) CH3 twist(68)

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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

LSDA/6-311++G(d,p)

Abbreviations: R – ring; b – bending; x – out-of-plane bending; s – torsion; trigd – trigonal deformation; symd – symmetric deformation; asym – antisymmetric deformation; ass – asymmetric stretch; ss – symmetric stretch; ips – inplane stretch; ops – out-of-plane stretch; ipb – inplane bending; opb – out-of-plane bending; sb – symmetric bending; ipr – in-plane-rocking; opr – out-of-plane rocking.

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reveals the advantages of higher basis set for quantum chemical applications. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] Fig. 12. Observed and calculated FT-Raman spectra of 2-methyl-1-vinylimidazole. (a) Observed, (b) calculated with B3LYP/6-311++G(d,p) and (c) calculated with LSDA/6-311++G(d,p).

[13] [14] [15] [16] [17] [18] [19] [20] [21] [22]

[23] Fig. 13. Observed and calculated FT-IR spectra of 2-methyl-1-vinylimidazole. (a) Observed, (b) calculated with B3LYP/6-311++G(d,p) and (c) calculated with LSDA/6311++G(d,p).

out-of-plane bending vibrations of the title compound are completely assigned and are presented in Table 11.

[24] [25] [26] [27] [28] [29] [30] [31] [32]

Conclusion In this study, the spectroscopic properties of 2M1VIM were examined by FT-IR, FT-Raman and NMR techniques. Quantum chemical calculations help us to identify the structural and symmetry properties of the molecule. A comparison of the result of experimental and theoretical study gave us a full description of the geometry and vibrational properties of the title molecule. The chemical shifts were compared with experimental data, showing a very god agreement both for 13C and 1H NMR. The electronic properties were also calculated. HOMO and LUMO energy gap explains the eventual charge transfer interactions takes place within the molecule. The calculated geometric parameters and vibrational frequencies obtained with DFT method are in well agreement with the experimental values obtained for the investigated molecule. In summary, a complete characterization study of the title compound was present this paper. The excellent agreement of the calculated and observed vibrational spectra

[33]

[34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47]

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