The pyrimidine ring outside of the rigid core ring of liquid crystal molecules used as a polar mesogenic group, can effectively increase the molecular dipole moment and intermolecular force, improve the dielectric anis-otropy of the compounds, reduce the driving voltage of the liquid crystal, and also favor to form some smec-tic phases. In this paper, where pyrimidine acetyleneisused as the central structural unit and isothiocyanide asthe end group, we could see that a series of liquid crystal compounds (nBTM-NCS) about five compounds were desi...