Fluorine-19 FT–NMR studies of CF3-containing systems dissolved in smectic liquid crystal solutions

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Abstract
The fluorine‐19 shielding anisotropies of CF3Cl, CF3Br, CF3I, and CF3CCl3 have been determined from analyses of fluorine NMR spectra in partially ordered smectic liquid crystal solutions. The high degree of orientation and increased solubility produced in the smectic phase leads to measurements of σ∥−σ⊥ for each of these systems to relatively high accuracy. The anisotropies obtained for the trifluorohalomethanes are found to increase in the order: CF3Cl, −13.4±0.5 ppm; CF3Br, 2.7±0.3 ppm; CF3I, 16.8±0.2 ppm. The quantity σ∥ is approximately constant for each of the CF3X molecules studied. This feature permits an estimate of the shielding and spin–rotation constants of CF4.