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Infrared Rotatory Dispersion of Induced Cholesteric Phases Measured with a Fourier Transform Spectrophotometer

Volume 35, Number 3 (June 1981) Page 279-280

Belz, H.H.; Jede, F.; Schrader, B.

When chiral molecules are dissolved in nematic liquid crystals they induce a cholesteric phase. Such an induced cholesteric phase consists of left- or right-handed helical arrangements of the liquid crystal molecules. The handedness of the helical arrangements depends on the absolute configuration of the chiral "guest" molecules. A properly ordered cholesteric phase shows a pronounced infrared rotatory dispersion (IRD) with strong "absorption cotton effects" in the vicinity of their infrared absorption bands and a "reflexion, cotton effect" the wave-length of which is equal to the pitch of the helix. This IRD can be used to determine the absolute configuration of the chiral guest molecules as well as for the verification of chirality, the determination of enantiomeric purity, and the discrimination of enantiomers. The IRD can be measured with a specially developed single beam dispersive spectrometer with a detectivity of about 0.01°.