Infrared and Raman spectra, conformations and ab initio calculations of 2-chloroethyl TRIFLUOROSILANE (cas 13465-71-9)

Add time:08/11/2019    Source:sciencedirect.com

The infrared spectra of 2-chloroethyl trifluorosilane (ClCH2CH2SiF3) were recorded in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm−1. Spectra of the compound isolated in argon and nitrogen matrices at 10 K and variable temperature spectra in liquified xenon were obtained. Raman spectra of the liquid were recorded at various temperatures between 298 and 163 K, and the amorphous and crystalline solids studied. The spectra of 2-chloroethyl trifluorosilane showed the existence of two conformers—anti and gauche—present in the vapour and in the liquid. Large variations in the infrared and Raman spectra occurred during the annealing and an intermediate, probably metastable crystal appeared at ca. 125 K with pronounced crystal splitting and apparently containing both conformers. More than 15 infrared and Raman bands present in the fluid phases and in the 125 K crystal vanished in the stable crystal formed at ca. 160 K. From intensity variations with temperature of five Raman band pairs, a ΔH°(anti-gauche)=0.8±0.3kJmol−1 was obtained in the liquid, and in liquid xenon under pressure a ΔH value of −0.7±0.1kJmol−1 was obtained from IR spectra. Annealing experiments indicate that the anti conformer has the lower energy in argon and nitrogen matrices as well as in xenon, and the barrier seemed to be ca. 8 kJ mol−1. Ab initio calculations were performed using the Gaussian 94 program with the HF/6-311G* basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 3.8 kJ mol−1 giving anti as the low energy conformer.

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