Handedness cholesteric correlations

Some Correlations Between Molecular and Cholesteric Handedness... 

In this report, we shall attempt to review critically works correlating the molecular chirality to the cholesteric handedness. 

Before attempting to develop any theory correlating molecular to cholesteric handedness, one must be completely sure of the experimental data. A cholesteric phase is fully described by its handedness and pitch, and often also knowledge of the pitch variations with temperature is fundamental. In particular, the determination of the handedness is quite a delicate matter. Before discussing the methods currently used to determine handedness and pitch, the principal textures of the cholesteric phase must be briefly reviewed The planar or Grandjean textures are obtained in thin cells by rubbing the cell walls (with... 

Some of these cholesteric systems are well-characterized The structure and handedness of the macromolecule is unequivocally known and so is the pitch and handedness of the cholesteric phase. A few attempts were made to correlate the polymer structure to the cholesteric handedness. 

Sq and negative Hq (Figure 7.12), so the handedness of the polymers are correlated to those of the cholesteric phases and the apparent discrepancy depends only on the comparison of the two results at a single temperature. Also in these cases the most common model of Figure 1.9a seems to be followed.46 It should be remarked that in all these cases, Hq and Sq have opposite signs.41... 

As mentioned in the introduction, the first empirical correlation between the absolute configuration of dopants and the handedness of induced cholesterics was proposed in 1975.20 The first attempt to find a general correlation was a few years later Krabbe et al.58 related the sense of the cholesteric to a stereochemical descriptor of the dopant based on the effective volume of the substituents and listed many compounds following this rule. However, exceptions were described at that time,59 and, furthermore, this approach neglects the role of the structure of the nematic solvent in determining the sense of the cholesteric. It is well known that chiral compounds may induce cholesterics of opposite handedness in different nematics.60,61... 

For an electrostatic interpretation of the formation of the cholesteric phase of DNA, which does not give, however, a stereochemical correlation between the macromolecular and cholesteric handedness, see Komyshev, A. A. Leikin, S. Phys. Rev. Lett. 2000, 84. 

Gottarelli, Giovanni, Some Correlations Between Molecular and Cholesteric Handedness, 24, 425. Graczyk, P. R., Anomeric Effect Origin and Consequences, 21, 159. 

That both phenomena arise as a consequence of macroscopic solvent order and not Intimate solvent-solute Interactions Is clear Saeva and 01In (75) have shown that solute LCICD spectra can be observed In twisted nematic phases only Nakazaki et al. (76) find an excess of one enantiomer of hexahelicene Is produced photochemlcally from achiral precursors In twisted nematic phases no LCICD spectra or optical Induction occurs In untwisted nematic phases and the handedness of the twist can be correlated with the sign of the LCICD and the preferred product enantiomer. Furthermore, Isotropic phases of cholesteric mixtures display no discernible LCICD spectra (12, 67) and the enantiomeric excesses In products of photolablle reactants In Isotropic phases are near zero (51). 

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