We have undertaken the study of the physical properties e.g. density, optical birefringence and x-ray diffration of three liquid crystalline compounds having bicyclohexane rigid core and isolated C=C double bond in the chain. The physical properties of these liquid crystals are strongly affected by the positional changes of the double bond. We have measured the refrative indices (no, ne) for three diffarent wavelengths and calculated the polarizability values, (αo, αe) different temperatures. It is found that for all the compounds optical birefringence is very low (Δn < 0.1). We have also calculated the intermolecular distance, pseudo layer spacing, correlation length and the orientational order parameter values at different temperatures from low angle x-ray diffraction photographs of aligned samples. Orientational order parameters at different temperatures were calculated both from birefrigence and x-ray study.