Add time:08/01/2019         Source:sciencedirect.com

The infrared spectra of Dimethylvinylsilane (cas 18243-27-1) and dimethylvinylsilane-d1 (CH2CH(CH3)2SiH(D)) were recorded in the vapour phase and as amorphous and crystalline solids in the 4000–50 cm−1 range. Moreover, they were isolated in argon and nitrogen matrices at ca. 5 K, and the parent molecule was dissolved in liquefied krypton between 218 and 173 K and the spectra recorded in the range 3100–450 cm−1. Raman spectra were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of the amorphous and crystalline solids were obtained at 50 K (in the infrared) and at 80 K (in the Raman spectra).The compound exists as two conformers, probably syn and gauche, and probably eight infrared and Raman bands present in the vapour, liquid and amorphous states in the parent molecule and in the isotopomer clearly vanished after crystallization. The intensity variations with temperature of one band pair in the liquid phase Raman spectra of the parent molecule and the d1 isotopomer were used for van't Hoff plots. These gave a value of 0.9±0.3 kJ mol−1 for ΔH(syn–gauche). Variable temperature studies of the infrared spectra in liquid krypton resulted in the value ΔH(syn–gauche)=0.7±0.04 kJ mol−1. The gauche conformer had the lower energy and was also present in the crystal. Intensity changes were detected when the matrix spectra were annealed to 37 K (argon) or 34 K (nitrogen) revealing that the gauche conformer was the more stable in the matrices.Ab initio calculations were carried out with the gaussian 98 program at the HF/6-311G*, RHF/6-311G* and MP2/6-311+G(2d,2p) levels and the vibrational frequencies for the syn and gauche conformers including infrared and Raman intensities were calculated. After appropriate scaling, a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers.

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