Phase- and glass-transition phenomena due to the same configurational order–disorder mechanism in crystalline racemic sec -butylcyclohexane

We report molar heat capacities for racemic sec-butylcyclohexane (s-BCH) measured by the adiabatic calorimetric method within the temperature range from 14 to 200 K. In the crystalline state, we identified the presence of a second-order phase transition and a glass transition phenomenon, both originating from the same configurational degree of freedom. The phase and glass transition temperatures T trs and T g were determined to be (136.7 ± 1.0) and (100 ± 1) K, respectively. The entropy of phase transition was estimated to be Δtrs S m = 1.4 J K−1 mol−1 ≈ (1/4) R ln 2. The phase transition was judged to be of an order–disorder type on the basis of the fact that the glass transition occurred in the low-temperature heat-capacity tail. The entropy was interpreted to suggest that four molecules in the crystalline state constitute a unit for producing two distinct configurations in the coexistence of (d)- and (l)-s-BCH.