The vibrational spectra of some trifluoromethyl derivatives of selenium and phosphorus

Wahi, Parmod Kumar (1972) The vibrational spectra of some trifluoromethyl derivatives of selenium and phosphorus. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis describes a detailed study of the vibrational spectra of some trifluoromethyl compounds of selenium and phosphorus: CF₃SeX (X = C1, Br, CN, CH₃ and CF₃), (CF₃Se)₂, (CF₃)₃P, (CF₃)₂PF and CF₃PF₂. The compounds were prepared by literature methods with slight modifications in some oases. Gas-phase infrared spectra were recorded in the range 4000 - 200 cm⁻¹ and liquid-phase Raman spectra from 4000 - 50 cm⁻¹. Raman spectra were excited by the appropriate lines of an argon-krypton mixed gas laser. Although some vibrational wavenumbers had been previously reported for most of these compounds, there were no detailed assignments. Since this work was completed an assignment of (CF₃)₃P has been published, which is somewhat in agreement with the conclusions reached here. The vibrational spectra of all these compounds have been analysed and almost all assignments made, using Raman depolarisation ratios, analogy with similar compounds and the gas-phase infrared band contour study. The infrared band contour study has proved to be very useful in confirming some of the previous assignments and making many fresh assignments. The band contour study has shown that for the molecules containing one CF₃ group, the in-plane and out-of-plane C-F stretching and CF₃ asymmetric deformation modes show a slight splitting. For the molecules containing more than one CF₃ group, the in- and out-of-phase symmetric CF₃ deformation modes are always nearly degenerate and the in-phase mode is strong in the Raman, while the out-of-phase mode is strong in the infrared. The bands corresponding to CF₃ symmetric deformation and many other modes have been found to show POR structures. The PR separations for gas-phase infrared bands have been calculated using the recently reported method of Seth-Paul et al. The calculated PR separations show good agreement with the experimental values. As for many trifluoromethyl-phosphorus compounds studied earlier, here also the C-F symmetric stretching mode has been found to lie at higher wavenumbers than the C-F asymmetric stretching mode.

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