High pressure and low-temperature polymorphism in cyclopentanol

Abstract

The polymorphism of cyclopentanol (C 5 H 10 O) has been investigated as a function of temperature at ambient pressure and as a function of hydrostatic pressures to 3.7 GPa at room temperature. Differential scanning calorimetry (DSC) and Raman spectra reveal that two plastic phases and two fully ordered crystalline phases are formed during cooling. High pressure Raman and infrared spectra show that cyclopentanol undergoes two-phase transformations. At around 0.6 GPa, the liquid cyclopentanol transforms to a solid plastic structure. On further compression to 1.9 GPa, one fully ordered crystalline phase is observed. Based on pieces of evidence such as peak splitting and emergence of new peaks, it can be concluded that the ordered crystalline structure has a lower symmetry. In addition, the decrease in the wavenumber of the O-H stretching modes at low temperature and high pressure suggests the ordered crystalline phases are characterized by the formation of hydrogen-bonded molecular chains.