Compounds of the formula ##STR1## wherein X.sup.1 denotes fluorine or chlorine and X.sup.2 denotes hydrogen, fluorine or chlorine; R.sup.1 is 3E-alkenyl, 4-alkenyl, 2E-alkenyloxy or 3-alkenyloxy; n stands for the number 0 or 1; one of the groups Y.sup.1 and Y.sup.2 is a single covalent bond, --COO--, --OOC--, --CH.sub.2 CH.sub.2 --, --CH.sub.2 O-- or --OCH.sub.2 -- and the other of the groups Y.sup.1 and Y.sup.2 is a single covalent bond; and rings A.sup.1 and A.sup.2 each individually are substituted or unsubstituted trans-1,4-cyclohexylene, in which optionally 2 non-adjacent CH.sub.2 groups are replaced by oxygen, or substituted or unsubstituted 1,4-phenylene, in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen; with the proviso that X.sup.2 denotes fluorine or chlorine and/or Y.sup.1 or Y.sup.2 denotes --CH.sub.2 O-- or --OCH.sub.2 -- when simultaneously X.sup.1 is fluorine and R.sup.1 is 3E-alkenyl,and their use for liquid crystalline mixtures and electro-optical purposes.