SOLID-PHASES AND PHASE-TRANSITIONS OF CYCLOHEPTANE

The phases and phase transitions of solid cycloheptane are examined wi th differential thermal analysis, with two new findings. Phase I sampl es cooled below similar to 200 K directly transform to phase III, not phase II as reported earlier. Phase III readily supercools through the III-IV transition, yielding a glassy crystal IIIg or transforming int o a previously unknown metastable phase, III', depending on details. T hese findings impact the identification of the phases studied in previ ous reports. Deuterium NMR of phase III shows that the reorientations are not isotropic, indicating that no molecules reside in sites of cub ic symmetry. The deuterium spectrum suggests several inequivalent site s in phase III.