Polymorphism of trans-1,4-Cyclohexanediol: Conformational Isomorphism

In this work, an investigation on the polymorphism of trans-1,4-cyclohexanediol is performed. Polymorph screening is carried out by crystallization from solutions, by sublimation, and by cooling the melt, and a combined approach using differential scanning calorimetry, polarized light thermomicroscopy, and X-ray diffraction is employed in the results interpretation. Three solid forms, I, II, and III (Steiner et al.J. Chem. Soc., Perkin Trans. 2 1998, 371-377), are identified, I and II, for the first time, and their relative stability established. The crystal structure of polymorph 11 is resolved by single crystal X-ray diffraction: a monoclinic P2(1)/a space group Structure. This polymorph, as polymorph III (Steiner et al. J. Chem. Soc., Perkn Trans. 2 1998, 371-377), exhibits Unusual conformational isomorphism, that is, the coexistence of the biequatorial and the biaxial conformers in the same crystal structure.