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

Abstract

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 II is resolved by single crystal X-ray diffraction: a monoclinic P21/a space group structure. This polymorph, as polymorph III (Steiner et al. J. Chem. Soc., Perkin 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.

[2](1,3)Adamantano[2](2,7)pyrenophane: A Hydrocarbon with a Large Dipole Moment

“…However,t he energy difference of the two types of symmetries is much larger (6.3 kcal mol À1 )f or 3 than for 12 (0.7 kcal mol À1 ), and this explains why 3 crystallizes exclu-sively in its C s -symmetric form, whereas 12 does so in two almost equally stable crystal forms.T he appearance of different conformers of the same molecule equally distributed in the same crystal is termed conformational isomorphism, [29] which is not common. [30] In principle,c rystallization of conformers should be widespread, as even toluene crystallizes in two rotameric forms. [31] We found 486 hits in the Cambridge Structural Database of pure hydrocarbons which crystallize with more than one molecule in the asymmetric unit (Z' > 1).…”

Aplicações Tecnológicas do Polimorfismo Farmacêutico

“…Neste caso, alterações na estrutura intramolecular não são signifi cativas. Quando torções no esqueleto molecular são associadas a mudanças no ordenamento a longo alcance, confi gura-se o polimorfi smo conformacional, o qual é comumente observado em diferentes estruturas de moléculas pouco rígidas [14][15][16][17][18][19] . Na maioria dos casos, alterações conformacionais estão relacionadas a mudanças nos padrões de interações intermoleculares 9,15 .…”

Tuning the solid-state fluorescence of chalcone crystals via molecular coplanarity and J-aggregate formation

“…9,10 Molecules with conformational exibility usually show a larger extent of freedom than rigid ones so that a wide range of polymorphism might be obtained from them. [11][12][13] Current research on the solid state uorescence of polymorphism indicate that stacking geometries of molecules and intermolecular electronic interactions in the solid state have a signicant inuence on uorescent properties of organic luminescent polymorphs. [14][15][16][17] And many studies on luminescence properties suggest that J-aggregate formation is benecial to uorescence emission.…”