Understanding the self-assembling process in crystalline cyclooctitols: an insight into the conformational flexibility of medium-sized rings

Abstract

The crystal structures of two closely related cyclooctitols 1 and 2, in the form of their acetonide derivatives, have been analysed, in order to investigate the interrelationship between the preferred mode of self-assembly and conformation of the eight-membered carbocyclic ring in the solid state. While dissimilar in their conformation, the diols 1 and 2 exhibit remarkable similarity in their molecular packing which appear to define an interesting motif in the form of repeating figures of "8", with the polar hydroxyl groups forming the interior "links" and the lipophilic molecular bulk the exterior "bends". Observed differences in the conformation of the cyclooctane ring in crystalline 1 and 2vis-a-vis that deduced on the basis of energy minimization could be related to an interplay in the degree of pliancy of the eight-membered ring and conformation-directing ability of competing inter- and intramolecular hydrogen bonds.