Vibrational spectroscopic study of the three solid phases of bicyclo[2.2.2]octene

The three solid phases of bicyclo[2.2.2]oct-2-ene were characterized by vibrational spectroscopy at low temperatures and high pressures. Bicyclooctene undergoes a phase transition at 176 K on cooling (phase I --> phase II) and then another at ca 95 K (phase II --> phase III). On compression at room temperature, these same transitions occur at 7.9 +/- 1.0 kbar and ca. 15 kbar. The low-frequency Raman spectra show that phase I is isotropically disordered, whereas phase II is anisotropically disordered. The crystal structure of phase II is, however, similar to that of phase III, and is suggested to be tetragonal.