Phase transitions in adamantane derivatives: 2-chloroadamantane

Abstract

The phase transition behaviour of 2-chloroadamantane, 2-C10H15Cl, has been investigated by differential scanning calorimetry (DSC), and FT-IR and Raman spectroscopy. Two transitions were detected by both DSC and vibrational spectroscopy at 231 and 178 K, on cooling, and at 242 and 227 K, on heating. The measured enthalpies were 8.3 kJ mol−1 for the first transition (phase I → phase II), and 0.47 kJ mol−1 for the second (phase II → phase III). The entropies were 35 and 2.3 J K−1 mol−1, respectively. These are similar to those observed for other 2-substituted adamantanes, but significantly different from those for 1-substituted derivatives. The large hystereses observed for the two transitions are independent of the DSC scanning rate and are characteristic of first-order phase transitions. The dramatic differences observed in the vibrational spectra of phases I and II provide clear evidence of an order–disorder transition at about 235 K.