News on Inositol Liquid Crystals1

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Abstract
A greater number of selected, partially O-alkylated derivatives of three (myo-, scyllo-, and chiro-) inositols, stereoisomers of 1,2,3,4,5,6-hexahydroxycyclohexane, as well as of hexahydroxybenzene and tetrahydroxy-l,4-benzoquinone were synthesized and characterized by usual methods. From the study of the various liquid crystalline target compounds (long-chained alkyl ethers) by polarizing microscopy and differential scanning calorimetry it emerges that the occurrence, type, and stability of their meso-phases are clearly determined by the number, the position, and the stereochemical arrangement of both the hydroxyl groups and the alkoxy chains on the cyclohexane ring which is discussed in detail. Here, unsaturated six-membered ring units—for example quinoic or aromatic in character—as carriers of the numerous hydroxyl functions have been proved damaging to the exhibition of mesophases; our mul-tihydroxy model compounds of this type have not been found liquid crystalline. In general, it was found that axial hydroxy and alkoxy groups destabilize the smectic A or hexagonal columnar phase exhibited here. Moreover two types of mesophase transformation from hexagonal columnar to smectic A have been found, i) by changing the stereochemistry of two vicinal hydroxyl functions in a peg-shaped chiro-inositol diether (derived from quebrachitol) or ii) by blocking of a (special) equatorial hydroxyl function in a peg-shaped myo-inositol diether through etherification. A complete homologous stereoisomeric series (five members) of myo- and scyllo-inositol monoalkyl ethers with each a dodecyl chain at their respective oxygen functions is also presented; the three thermomesogenic ones of them exhibit the smectic A phase. In this connection and with regard to a homologous series of D-glucopyranose monoethers, molecular symmetry effects originating from the different localization of the one ether group in both homologous series on their ability/inability of mesophase formation are discussed in detail.