We report on a first experimental study of the molecular properties of nematic liquid crystals in the terahertz range. In the beginning, we extract the frequency and temperature dependent refractive index and absorption coefficient of the cyanobiphenyls 5CB, 6CB and 7CB from terahertz time domain spectroscopy measurements and investigate the impact of the alkyl chain length on the macroscopic liquid crystal characteristics, focusing especially on the pronounced odd and even effect. Next, we deduce the principle polarizabilities and the order parameter S by applying Vuks' approximation and Haller's approach. On this basis, we calculate the main polarizabilities along the longitudinal and transverse axis and link the observed terahertz properties to the molecular structure of the liquid crystals.