Heat capacity of solid tetrachloro-p -benzoquinone (chloranil) between 11 and 300 °K. Phase transition at 92 °K

Molar heat capacity of solid chloranil was measured between 11 and 300 °K with particular attention to the phase transition at 92 °K. The heat and entropy of the transition were 38 J mol−1 and 0.41 J °K−1 · mol−1. The transition is of a lambda shape starting at 70 °K and ends at 100 °K. The anomalous heat capacity curve was explained by the soft librational mode theory. There is another large transition at about 570 °K. The shape and magnitude of the transitions are very sensitive to the long-range regularity of the structure and depend on the method of preparation.