Chiral β-hydroxycarbonyl compounds based on (−)-menthone: structure and behavior in liquid crystalline systems

It has been established by X-ray structural analysis that 2-(1′-biphenyl-4-yl-1′-hydroxy)methyl- p-menthan-3-one, one of the products of the reaction of (−)-menthone triisopropyloxytitanium enolate with 4-phenylbenzaldehyde, has a 1 R,2 S,4 S,1′S configuration. In crystals, this β-hydroxyketone adopts a chair conformation with equatorial methyl and isopropyl groups and an axial 2-(1′-biphenyl-4-yl-1′-hydroxy)methyl substituent. Unlike the stereoisomeric compound with the 1 R,2 S,4 S,1′S configuration, the exocyclic fragment of which has an intramolecular >C=O...H-O- hydrogen bond in crystals and solutions, in the crystals of the 1 R,2 S,4 S,1′S ketol under study, molecules are linked by a network of cooperative -O-H...O-H...O-H... hydrogen bonds. Based on the results of molecular mechanics calculations and experimental data of¹H NMR and IR spectroscopy, conformations of molecules of this compound, which are in equilibrium in solution, have been characterized. Based on data on spatial structures of stereoisomeric β-hydroxyketones and the character of H-bonds formed by these compounds, the characteristic features of the effect of these chiral alloying additives on the supramolecular structure and macroscopic properties of liquid crystalline systems have been interpreted.