The Vibrational Spectrum and Structure of Symmetric Tetrabromoethane and Its Deuterate Analogs

Abstract

Raman and infrared spectral studies have indicated the existence of rotational isomerism for substituted ethanes. Tetrabromoethane (CBr2H-CBr2H) is considered to exist in the trans and gauche forms. Therefore, the analysis of the Raman and infrared spectra entails the assignment of the vibrational frequencies to one or the other form. A partial assignment of this type has been made by Kagarise [1] for C2H2Br4. A more complete assignment could be made if knowledge of the vibrational frequencies of C2D2Br4 were available. In the present investigation the Raman and infrared spectra of C2H2Br4 and C2D2Br4 have been obtained. As the Raman and infrared spectra of C2H2Br4 obtained in this investigation are essentially the same as those reported by Kagarise [1], they will not be given here. As for C2D2Br4 the Raman displacements in cycles per centimeter, relative intensities, and depolarization factors (Δσ(1)ρ) are: 63(15)0.73; 112(13)0.55; 146(17)0.70; 175(19)0.68; 217(100)0.11; 434(7)0.77; 520(20)0.03; 603(6)0.35; 659(25)0.43; 793(2)0.82; 835(1)0.86; 873(3)0.72; 900(16)0.65 944(0)0.66?; 973(1)0.86; 1065(12)0.21; and 2228(12)0.34. The wave numbers in cycles per centimeter for the more prominent bands in the infrared spectrum of C2D2Br4 are: 430(s); 520(s); 569(m); 592(vs); 611(m); 656(vs); 833(vs); 900(vs); 976(vs); 1069(s); and 2232(vs). The Raman and infrared data for C2H2Br4 and C2D2Br4 have been compared to arrive at a complete assignment of the observed bands. As a check on the assignments, a normal coordinate treatment using the Wilson FG matrix technique has been carried out for the frans isomer of each molecule.