Phase transitions in adamantane derivatives: 1-fluoroadamantane

Abstract

The solid-state phase behaviour of 1-fluoroadamantane (1-C10H15F) has been investigated by differential scanning calorimetry, and by infrared and Raman spectroscopy. The phase transition occurs at 227 K on cooling and at 231 K upon heating, with average ΔHt and ΔSt of 1.65 kJ mol−1 and 7.3 J K−1 mol−1. The transition was also apparent in the low-temperature IR and Raman spectra by a sudden line narrowing, and characteristic spectral features of each phase were identified. Both phases I and II were disordered, and further cooling of phase II resulted in the formation of a glass. Attempts to induce a glass transition (predicted to occur at ~90 K) by slow heating were unsuccessful. Vibrational spectroscopic studies at high pressures showed a phase transition at 3.3 ± 1.0 kbar, upon compression. The phases formed under pressure were the same as those induced by lowering temperature. Key words: high-pressure infrared and Raman spectroscopy, phase transition, plastic crystal, orientational disorder.