Liquid-crystalline mustard oils

A mustard oil of the formula I

• R--(A.sup.1 --Z.sup.1).sub.n --A.sup.2 --Z.sup.2 --A.sup.3 --NCS (I)
• in which
• R is H or alkyl of 1-15 C atoms, in which one or two non-adjacent CH.sub.2 groups can be replaced by --O--, --CO--, --O--CO-- and/or --CO--O--,
• A.sup.1 and A.sup.2 are each an unsubstituted or monosubstituted or polysubstituted 1,4-cyclohexylene group, a piperidine-1,4-diyl or 1,4-bicyclo[2.2.2]octylene group or a 1,4-phenylene group which is unsubstituted or substituted by one or two F and/or Cl atoms and/or CH.sub.3 groups and/or CN groups and in which one or two CH groups can also be replaced by N,
• A.sup.3 is a 1,4-cyclohexylene group or a 1,4-phenylene group which is unsubstituted or substituted by one F atom,
• Z.sup.1 and Z.sup.2 are each --CO--O--, --O--CO--, --CH.sub.2 CH.sub.2 --, --CHCN--CH2--, --CH.sub.2 --CHCN--, --CH.dbd.CH--, --OCH.sub.2 --, --CH.sub.2 O--, --CH.dbd.N--, --N.dbd.CH--, --NO.dbd.N--, --N.dbd.NO-- or a single bond,
• n is 0, 1 or 2,
• Cy is 1,4-cyclohexylene and
• Phe is 1,4-phenylene.