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Determination of Bond Distances and Bond Angles in a Liquid Crystal with Hydrogen Bonding

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journal contribution
posted on 22.05.2003, 00:00 by Chibing Tan, B. M. Fung
The structure of a liquid crystal with intramolecular hydrogen bonding, 5-butoxy-2[(4-butylphenyl)azo]phenol, was determined by using X-ray diffraction of a single-crystal and NMR studies in the nematic phase. Because the uncertainties in the positions of the hydrogen atoms are quite large in the X-ray structure, some of the bond distances and bond angles of the mesogenic core were determined by the use of 13C NMR. For the liquid crystals in natural abundance, 1H−13C dipolar coupling constants were obtained from the 2D technique of proton-encoded local field spectroscopy. For an analogue with deuterium substitution in the hydrogen-bonded position, 2H−13C dipolar coupling constants were obtained from 1D 13C−{H} spectra. The dipolar coupling constants were used to calculate the order parameters of the phenyl rings, as well as the bond distances and bond angles in the hydrogen-bonded moiety.

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