Polymorphism in Cyclohexanol Reexamined

Abstract

Dielectric, visual, and calorimetric observations are brought together to explicate the relations between the four solid forms of cyclohexanol. Rotational form I is stable from the freezing point of 25 °C down to the transition point with non-rotational form III at −8.3 °C; however, form II can be supercooled well below that temperature. Nonr-rotational form II has a transition point with form I at −28.8 °C and is metastable with respect to form III down to about −64° at which point a transition point occurs between forms II and III. Non-rotational form pre-II has a transition point with I at about −44°, below which it is metastable with respect to form II. The approximate temperatures for the maximum rates of nucleation are as follows: for I → pre-II, −87°, for I → III, − 105°, for pre-II → -II, −75°. The approximate temperatures for the maximum growth velocities are as follows: for I → II, − 43°, for I → pre-II, −60°, for I → III, −32°. Analysis of I → pre-II growth rates following the theory of continuous growth leads to a transition temperature of −43.5°, a heat of activation of 9.3 ± 0.5 kcal/mol, and preexponential factor of 5.1 × 10⁹ cm/hr.