Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power

Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anis...

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Bibliographic Details
Published in:Molecular Crystals and Liquid Crystals 2015-02, Vol.608 (1), p.14-24
Main Authors: Bauer, Monika, Hartmann, Lutz, Kleinpeter, Erich, Kuschel, Frank, Pithart, Cornelia, Weissflog, Wolfgang
Format: Article
Language:English
Subjects:
Activation
ATR-FTIR
Chiral dopants
Correlation analysis
dielectric spectroscopy
Dielectrics
Dopants
Ephedrine
ephedrine/pseudoephedrine
Glass
H NMR
Helical
Helicity
Hydrogen bonds
molecular structure
NMR
Nuclear magnetic resonance
Spectroscopy
Thermodynamics
Twisting
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Summary:Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature 1 H NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C‒N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy.
ISSN:1542-1406
1563-5287
1527-1943
DOI:10.1080/15421406.2014.949592