Optically active compounds of the formula ##STR1## wherein rings A, B and C each independently are unsubstituted or each are 1,4-phenylene substituted with at least one of halogen-, cyano-, methyl- or methoxy in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen; R.sup.1 is a radical of an optically active terpene alcohol after cleavage of the hydroxy group or a group --(CH.sub.2).sub.m --C*HX.sup.1 --R.sup.3 ; R.sup.2 is a radical of an optically active terpene alcohol after cleavage of the hydroxy group or a group --(CH.sub.2).sub.n --C*HX.sup.2 --R.sup.4 ; m and n each independently stand for the number 0 or 1: C* denotes a chiral carbon atom; X.sup.1 and X.sup.2 each independently are fluorine, chlorine, cyano, methyl or methoxy; R.sup.3 and R.sup.4 each independently denote a group R, phenyl or phenyl substituted with R, with the proviso that R.sup.3 is different from X.sup.1 and R.sup.4 is different from X.sup.2 ; R is an alkyl group in which optionally one methylene group is replaced by oxygen and/or optionally one group CH--CH is replaced by a group C.dbd.C; with the proviso that R.sup.1 and R.sup.2 are not simultaneously 2-alkyl when rings A, B and C together are p-terphenyl,as well as liquid crystalline mixtures and their use for electro-optical purposes.