Cholesteric temperature resolution

In each mesophase mixture, the dominant atropisomer after photo or thermal resolution experiments was S(+). The sole exception occurred during irradation of a 3% BN solution in mixture C. Since the sample solidified partially during the experiment, the mechanism by which the R(-) atropisomer arose is unclear. The thermal lability of the atropisomers toward interconversion and the possible contribution of cholesteric contaminants in recovered BN samples make an accurate assessment of atropisomeric excess a formidable task. Extreme care was taken to handle all solutions containing BN during work-up at temperatures which preclude significant thermal racemization at 25°C, the half-life for racemization is ca. 10 h in normal isotropic solvents all manipulations were conducted at 4°C or below. 

Smectic and cholesteric phases have been somewhat less extensively investigated until recently, probably because of the lack of gross structure in the NMR signals from these phases. Dunell and his co-workers (1, 9, 10, 15, 29) have published extensively on the temperature dependence of the NMR signal from various alkali soaps. Their work, however, has been principally concerned with the definition of the crystal-mesomorphic transitions by NMR. Recently Lawson and Flautt (16, 17) have studied the NMR signals of the mesomorphic states of several surfactant and surfactant-water phases under high resolution conditions. 

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