Liquid crystalline medium

A liquid-crystalline medium comprising a mixture of polar compounds of positive or negative dielectric anisotropy, including one or more compounds of the formula I

• 105
• in which
• 106
• are
• a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH2 groups are optionally replaced by —O— or —S—,
• b) a 1,4-phenylene radical, in which one or two CH groups are optionally replaced by N,
• c) a radical selected from the group consisting of piperidine-1,4-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,
• where the radicals a), b) and c) are optionally monosubstituted or polysubstituted by halogen atoms,
• 107
• x, y and z are each, independently of one another, 0, 1 or 2,
• Z1, Z2 and Z3 are each, independently of one another, —CO—O—, —O—CO—, —CF2O—, —OCF2—, —CH2O—, —OCH2—, —CH2CH2—, —(CH2)4—, —C2F4—, —CH2CF2—, —CF2CH2—, —CF═CF—, —CH═CH—, —C≡C— or a single bond,
• X is F, Cl, CN, SF5, NCS, a halogenated or unsubstituted alkyl radical having 1 to 8 carbon atoms, in which one or more CH2 groups are optionally replaced by —O— or —CH═CH— in such a way that O atoms are not linked directly to one another,
• a is 0, 1 or 2
• b is 0, 1 or 2, and
• c is 0, 1 or 2, where a+b+c is ≦3.