In this work, we report the results of x-ray diffraction, density and birefringence measurements on three fluorinated liquid crystalline compounds having negative dielectric anisotropy. Small angle x-ray diffraction data from aligned samples have been analyzed to determine the orientational order parameter as a function of temperature. The order parameter values were also determined from birefringence measurements and the results were compared with mean field theory. Structural parameters like intermolecular distance and layer thickness (in smectic B phase), apparent molecular length (in nematic phase) have been determined and the order of the phase transition in these compounds has been discussed.