Determination of order parameters from carbon-fluorine dipolar coupling

A convenient NMR method for the determination of the order parameters for liquid crystals containing a fluorinated phenyl ring is described. The technique consists of measuring the carbon-fluorine dipolar coupling constants in the one-dimensional C-13 spectrum of the molecule. The order parameters may then be calculated for the fluorine-containing ring with a high degree of precision because of the excellent resolution afforded by the 1-D C-13 spectra. The method is used to determine the core order parameters for 4-n-hexyloxybenzilidene-4'-fluoroaniline (FAB-OC6). The results of the carbon-fluorine dipolar coupling method are compared with two established methods for determining the core order parameters of phenyl rings, namely deuterium NMR spectroscopy and SLF/VAS, a two-dimensional C-13 NMR spectroscopy. Some comments about the orientational properties of the fluorinated liquid crystal FAB-OC6 are made.