Liquid crystal compounds

A liquid crystalline mixture comprising at least two components, wherein at least one component is a compound of the formula ##STR17## wherein R is an alkyl group with 1 to 12 carbon atoms or a group of the formula ##STR18## ring A.sup.1 is 1,4-phenylene, which is unsubstituted or substituted with one fluorine atom, pyridine-2,5-diyl or pyrimidine-2,5-diyl;

• ring A.sup.2 is trans-1,4-cyclohexylene or trans-1,3-dioxane-2,5diyl;
• R.sup.1 is an alkyl group with 1 to 12 or an alkenyl or alkoxyalkyl group with 2 to 12 carbon atoms;
• X.sup.1 is fluorine, chlorine, or bromine and can also be trifluoromethyl, trifluoromethoxy or difluoromethoxy when R is an alkyl group with 1 to 12 carbon atoms, when ring A.sup.1 is 1,4-phenylene substituted with one fluorine atom, pyridine-2,5-diyl or pyrimidine-2,5-diyl, when ring A.sup.2 is trans-1,3-dioxane-2,5-diyl, or when X.sup.2 or X.sup.3 is fluorine;
• and
• X.sup.2, X.sup.3 each independently is hydrogen or fluorine.