INVESTIGATION OF THE PHASE-TRANSITION BEHAVIOR IN SOLID CYCLOHEPTANE

The phase transition behavior in solid cycloheptane has been investigated by differential scanning calorimetry and vibrational spectroscopy (infrared and Raman). The spectra of four stable phases and of two glassy crystalline phases have been obtained. The spectrum of the stable, low-temperature phase, phase IV, is very different from the spectra of the other phases, indicating that this is the only ordered phase. The observed low-frequency Raman spectra are consistent with isotropic reorientation and anisotropic reorientation, related to a molecular pseudorotation process, occurring in phases I and II and phase III, respectively. The spectra of the glassy crystalline phases indicate that these phases possess static disorder, which is related to that of the corresponding high-temperature phases. © 1990 American Chemical Society.