2,5-Bis(p-substituted phenyl)-1,3-oxathianes (5), newliquidcrystal compounds, and some corresponding 1,3-dioxanes were synthesized by the acetal formation reaction. The mesomorphic behaviors of compounds 5 were compared with those of the corresponding 1,3-dioxanes and 1,3-dithianes. Compounds 5 exhibited the lowest transition temperatures between nematic and isotropic phases. This seems to originate