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 Δ trs 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.