Temperature- and pressure-induced phase transitions in cyclobutanol

• Supercooled state and crystalline state are observed during cooling and heating.
• Two transitions are observed under high pressure for the first time.
• The hydrogen bond plays an important role in its phase transformations.

The phase transition and polymorphism of cyclobutanol (C4H8O) has been investigated at low temperature and high pressure. Differential scanning calorimetry (DSC) and Raman spectra reveal that a supercooled state is observed during the cooling process, while crystalline state is formed in the heating process. We also present pressure-induced phase transition of cyclobutanol by means of Raman and infrared spectroscopy. The results indicate that cyclobutanol undergoes two phase transformations during compression to 11.4 GPa. At around 0.9 GPa, the liquid cyclobutanol transforms to a solid crystal structure. Further compression to 1.4 GPa, another fully ordered crystalline phase is observed. Simultaneously, conformational change is observed accompanied by phase transition. In addition, the red shift of the O–H stretching modes with pressure suggests the ordered crystalline phases are characterized by the formation of hydrogen-bonded molecular chains. Finally, the phase transitions under high pressure or low temperature are reversible.

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