Abstract: Optically active compounds of formula (I), where X has a structure (II) and B is C.sub.1-12 alkyl, a chiral group or a group having a general structure (III), where R and R' are H, C.sub.1-12 alkyl, alkoxy, alkylcarbonyloxy, or alkoxycarbonyl, each ring (IV) and (V) is the same or different, A and D are single bonds or bridging groups, each a and d is 0 or 1; Z, Z' are CN, Cl, F, Br or CF.sub.3 ; provided when Z is CN or Cl, then when B is alkyl X-Y is not (VI) or (VII). Ferroelectric smectic liquid crystal mixtures containing these compounds are also described.