| Popis: |
The infrared and Raman spectra of trans-1,4-dichloro- and trans-1,4-di-bromocyclohexane were recorded in the region 4000-45 cm−1 as melts, as solutes in various solvents, as amorphous solids at −180 °C and in the crystalline state at various temperatures from −180 °C to 100 °C. Additional infrared studies of the vapours (140–190 °C), the solids under high pressure (1–50 kbar at ambient temperature) and dichroism of oriented polycrystalline films were carried out. Finally, Raman polarization ratios of the samples were measured in different solutions. Equilibrium mixtures of the trans-1,4-dichloro- and dibromo cyclohexanes in nearly equal amounts of ee and aa conformations were observed in the vapour phase, in the melts, in solutions and in the amorphous solids. In the crystals formed at room temperature both molecules existed predominantly in the ee conformation, with the chloro compound having a stable phase below and a disordered phase above 12 °C. When the chloro compound was evaporated onto a CsI window at −180 °C, both conformers were present in the amorphous solid. When annealed at temperatures below 10 °C, a crystal with molecules in the aa conformation was formed, above 12 °C, the crystal had molecules in the ee conformation. For the bromo compound no “aa crystal” was formed. When the “ee crystals” were exposed to high pressure the concentration of the aa conformer increased for both compounds and was almost exclusively present at 50 kbar and 50 °C. The spectra were interpreted in terms of C2h symmetry. The fundamental frequencies for both conformers were assigned and checked by the sum rule, and the rotational and vibrational partition functions were derived. |
