Vibrational Spectroscopic Investigations of Methacrylonitrile

C.Yohannan Panicker¹*, Hema Tresa Varghese², B.Harikumar³ and Asha Chandran³

¹Department of Physics, TKM College of Arts and Science, Kollam - 691 005, India. 

²Department of Physics, Fatima Mata National College, Kollam - 691 001, India.

³Department of Chemistry, TKM College of Arts and Science, Kollam - 691 005, India.

DOI : http://dx.doi.org/10.13005/msri/080214

ABSTRACT:

The vibrational wavenumbers of methacrylonitrile were calculated using Gaussian03 software package at different levels of theory and the fundamental modes are assigned. The predicted infrared intensities and Raman activities are reported. The first hyperpolarizability is calculated and the title compound is an attractive object for futures studies of nonlinear optics. The calculated wave numbers (B3LYP) are in agreement with the experimental values.

KEYWORDS: FT-IR; FT-Raman; DFT calculations; Hyperpolarizability

Copy the following to cite this article: Panicker C. Y, Varghese H. T, Harikumar B, Chandran A. Vibrational Spectroscopic Investigations of Methacrylonitrile. Mat.Sci.Res.India;8(2)

Copy the following to cite this URL: Panicker C. Y, Varghese H. T, Harikumar B, Chandran A. Vibrational Spectroscopic Investigations of Methacrylonitrile. Mat.Sci.Res.India;8(2). Available from: http://www.materialsciencejournal.org/?p=2656

Introduction

Methacrylonitrile is an aliphatic nitrile used extensively in the preparation of homo- and copolymers, elastomers, and plastics and as a chemical intermediate in the preparation of acids, amides esters and other nitriles. This aliphatic nitrile is also used as a replacement for acrylonitrile in the manufacture of an acrylonitrile/butadiene/ styrene-like polymer. Youcef et al.¹ reported the study of ETFE based radiation grafted poly(styrene sulfonic acid-co-methacrylonitrile) proton conducted membranes with increased stability. Several authors reported on the use of styrene/ acrylonitrile,^2,3 α-methylstyrene.styrene⁴ and p-methylstyrene/tert-butyl styrene⁵ as grafting monomers. Oh et al.⁶ reported an ab initio study of the molecular elimination reactions of methacrylonitrile. Extensitve studies have unveiled the aldoxime-nitrile pathway in microorganisms^7,8 and the biological metabolism for nitrile compounds is increasingly noticed.⁹ In the present study, the IR, Raman and theoretical calculations of the wavenumbers of the title compound are reported.

Experimental

The FT-IR spectrum was recorded on a DR/Jasco FT-IR-6300 spectrometer in KBr pellets. The spectral resolution was 4 cm^-1. The FT-Raman spectrum was obtained on a Bruker RFS 100/S, Germany. For excitation of the spectrum the emission of Nd:YAG laser was used, excitation wavelength 1064 nm, maximal power 150 mW, measurement on solid sample. The spectral resolution after apodization was 4 cm^-1.

Computational Details

The vibrational wavenumbers were calculated using the Gaussian03 software package on a personal computer.¹⁰ The computations were performed at HF/6-31G(d) (6D, 7F) and B3LYP/6-31G(d) (6D, 7F) levels of theory to get the optimized geometry and vibrational wavenumbers of the normal modes of the title compound. DFT calculations were carried out with Becke’s three-parameter hybrid model using the Lee-Yang-Parr correlation functional (B3LYP) method. The wavenumber values computed contain known systematic errors¹¹ and we therefore, have used the scaling factor values of 0.8929 and 0.9613 for HF and DFT basis sets. Parameters corresponding to optimized geometry of the title compound are given in Table 1. The absence of imaginary values of wavenumbers in the calculated vibrational spectrum confirms that the structure deduced corresponds to minimum energy.

Table 1: Geometrical parameters

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Results and Discussion

The observed IR and Raman bands and calculated (scaled) wavenumbers and assignments are given in Table 2. In the spectra of methyl esters the overlap of the region in which both asymmetric stretching¹² υ_asCH₃ absorb with a weak to medium intensity (2985 ± 25 and 2970 ± 30 cm^-1) is not large and regularly seen above 3000 cm^-1. The computed wavenumbers (DFT) of modes corresponding to υ_asCH₃ groups are 3023, 2992 cm^-1. For the title compound, band at 2966, 2931 cm^-1 in the IR spectrum and 3014, 2995 cm^-1 in the Raman spectrum is assigned as asymmetrical methyl stretching modes. The symmetrical stretching mode υ_sCH₃ is expected in the range 2920 ± 80 cm^-1 in which all the three C-H bonds extend and contract in phase.¹² The bands seen at 2937 (DFT), 2890 (IR) cm^-1 and 2933 cm^-1 (Raman) are assigned as these modes. Two bending vibrations can occur within a methyl group. With methyl esters the overlap of the regions in which methyl asymmetric deformations are active (1460 ± 25 and 1450 ± 15 cm^-1) is quite strong, which leads to many coinciding wavenumbers.¹² This is obvious, not only for the asymmetric deformations, but also for the symmetric deformations¹² mostly displayed in the range 1380 ± 15 cm^-1. The B3LYP calculations give 1463, 1447 and 1385 cm^-1 as asymmetric and symmetric CH₃ deformations for the title compound. Experimentally δ_asCH₃ vibration is observed at 1452, 1428 cm^-1 in the IR spectrum while δ_sCH₃ vibrations are observed at 1381 cm^-1 in the IR spectrum, 1404 cm-1 in the Raman spectrum. The methyl rocking wavenumbers are expected in the regions¹² 1100 ± 95 and 1080 ± 80 cm^-1. The bands calculated at 1046, 1004 cm^-1 are assigned as rocking modes of the methyl groups. The rocking mode is observed at 1018 cm^-1 in the IR spectrum.

Scheme 1:

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 Table 2: Vibrational assignments

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The vibrations of the CH₂ group, the asymmetric stretch υ_asCH₂, symmetric stretch υ_sCH₂, scissoring vibration ωCH₂ and wagging vibration υCH₂ appear in the regions 3000 ± 50, 2965 ± 30, 1445 ± 55 and 1350 ± 85 cm^-1, respectively.^12,13 The CH₂ stretching bands are observed at 3096, 2993 in IR spectrum and at 3114, 3041 cm^-1 in the Raman spectrum. The scissoring and wagging vibrations were assigned at 1407 and 1247 cm^-1 theoretically. The twisting mode τCH₂ is assigned at 921 cm^-1 theoretically as expected¹².The rocking mode¹² ρCH₂ is expected in the range 895 ± 85 cm^-1 and the band at 728 theoretically. The torsional mode of CH₂ is seen the low wavenumber range¹². The CH₂ modes are reported at 2994, 2961 (stretching) and at 1143, 1168 cm^-1(twisting) by Chandra et al..¹⁴ The methylene wagging exhibits absorption bands in the range 1360 ± 25 cm^-1 and twisting mode in the range^15-17 1290± 40 cm^-1.

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