In this work, we present the effect of electric field on 4-(trans-4$^\prime$-n-alkyl-cyclohexyl) isothiocyanatebenzene(nCHBT) liquid crystal (LC) molecules. Under the influence of an electric field, the birefringence exhibits the even–odd effect while order parameter, HOMO–LUMO gap, magic angle, isotropic polarisability, range of director angle and the refractive index do not exhibit any even–odd effect. The extension of the alkyl chain length of the nCHBT liquid crystal molecule exhibits the even–odd effect for the dipole moment and temperature from nematic to isotropic phase transition while the HOMO–LUMO gap remains constant. Still, order parameters, isotropic polarisability and refractive index have continuously increased. The odd carbon atom numbers present higher values than the even carbon atom numbers of the alkyl chain for the phase transition temperature. The nCHBTLC molecule expresses the order parameter, and birefringence is reciprocal to each other. For the whole series, there is an increase in order parameter, and a decrease in birefringence. The influence of the external electric field is analternative to the temperature for the optical parameter of nCHBT LC.