An infrared and Raman spectroscopic study of rotational isomerism in 2,3-dimethyl-2,3-diphenylbutane, the fluoro-, chloro-, and bromo-substituted 2,3-dimethyl-2,3-di-p-halogenophenylbutanes and 1,2-diphenyltetrachloroethane
The simplicity of the Raman spectra of the solid compounds named in the title coupled with the general absence of corresponding frequencies from the i.r. spectra of the solids suggests the existence of only the trans-rotamer in the solid phase. A mixture of both trans- and gauche-rotamers in solution is confirmed by the appearance of extra bands in the i.r. and Raman spectra of various solutions. A discussion is given of the assignment of the stronger bands to fundamental vibrational frequencies in relation to the differences between the spectra of solids and solutions. The relatively strong intensities of the bands due to the gauche-rotamer in all five compounds indicate that, in solution, the proportion of the gauche-rotamer is appreciably higher than that of the trans.