VIBRATIONAL SPECTROSCOPIC STUDY OF THE TEMPERATURE-INDUCED AND PRESSURE-INDUCED PHASE-TRANSITION OF NORBORNYLENE

The order-disorder phase transition in norbornylene, bicyclo[2.2.1]hepta-2-ene, has been investigated by differential scanning calorimetry, low-temperature infrared and Raman spectroscopy, and high-pressure infrared spectroscopy. When induced by low temperature, a 13 K hysteresis was associated with the phase transition, which occurred at 114 K on cooling. The same transition could be induced by applying 14.9 +/- 0.3 kbar of pressure, exhibiting a 1.6 +/- 0.7 kbar pressure hysteresis. The volume change of the transition, DELTA-V(t), was calculated to be 3.1 +/- 1.0 cm3 mol-1. The observed correlation coupling effects suggest that the factor group of the ordered phase is monoclinic or orthorhombic (C2v or C4v) with two molecules per unit cell, or tetragonal (C2 or C-sigma) with Z = 4.