Liquid crystalline composition for the use in a twisted nematic cell

Abstract: The invention relates to nematic liquid crystalline compositions comprising a group (A) with one or more components exhibiting a positive dielectric anisotropy (Δε) and a group (B) with one or more components exhibiting a neutral dielectric anisotropy characterized in that (a) at least one component of group (A) is a compound of the formula I (b) at least one component of group (B) is a compound of the formula V wherein R¹, R², Y¹, Y², X, Z, Z¹, m, n, o and r have the meaning given for claim 1.

Description: The invention relates to nematic liquid crystalline compositions comprising a group (A) with one or more components exhibiting a positive dielectric anisotropy (Δε) and a group (B) with one or more components exhibiting a neutral dielectric anisotropy characterized in that (a) at least one component of group (A) is a compound of the formula I wherein R¹ is an alkyl or alkenyl residue each with up to 16 C atoms, wherein one or two non-adjacent CH₂-groups of these residues may be replaced by -O-, -S-, -CO-O-, or -O-CO-, E¹ is -CH₂CH₂- or -CH=CH-, Q is -CO- or -CH₂-, Y is halogen or CN, and m is 1 or 2 or a compound of the formula II wherein R¹, E¹, Y and m have the meaning given for formula I, or a compound of the formula III wherein R¹ is an alkyl or alkenyl residue each with up to 16 C atoms, wherein one or two non-adjacent CH₂-groups of these residues may be replaced by -O-, -S-, -CO-O-, or -O-CO, E² is -(CH₂) n - or -CH=CH-(CH₂) n-2 - X and Z are each independently H or F, Y¹ is F, Cl, NCS, CF₃, OCF₃ or OCF₂H, m is 1 or 2, n is 1, 2 or 3, o is 0 or 1 and with the proviso that m is 2 or n is 2 or 3 in the case that Y¹ is F, Cl or NCS, or a compound of the formula IV wherein R¹ and m have the meaning given for formula I, and Z¹ is -(CH₂)₄-, -(CH₂)₃-O- or -CH=CH-CH₂CH₂- Y² is CF₃, OCF₃ or -CH=CH-CF₃, and r is 0 to 7, or that (b) at least one component of group (B) is a compound of the formula V wherein R¹, E¹, Q and m have the meaning given for formula I, and R² is an alkyl or alkyl residue with up to 16 C atoms wherein one or two non-adjacent CH₂ groups of these residues may be replaced by -O-, -S-, -CO-O- or -O-CO- or a compound of the formula VI wherein R¹, R 2, E¹ and m have the meaning given for formula V. The invention was based on the object of discovering that new liquid crystalline composition with advantageous values for optical and dielectric anisotropy for the use in twisted nematic cells can be obtained by admixing a group (A) with one or more components exhibiting a positive dielectric anisotropy and a group (B) with one or more components exhibiting a neutral dielectric anisotropy wherein at least one component is a compound of the formulae I, II, III, IV (group A) or V, VI (group B). The compounds of the formulae I and III are embraced by the broad general formula of DE-OS-32 25 290 but neither compounds with laterally fluorine substituents are disclosed there nor is described how to prepare them. The compounds of the formulae II and VI are embraced by the broad general formula of DE-OS 34 08 882. But none of them describes the synthesis of the laterally fluorinated compounds of the formulae II and IV. The non-fluorinated 4-substitued phenyl esters of 3-(4-alkylcyclohexyl)-propionic acid are described by DD-OS-155-078 and 155 063. Similar compounds are known from the Japanese Patent Applications J 60215652 and J 61010553 which claim 2-phenylethylesters of 4-alkylcyclohexylene carboxylic acids and from the Japanese Patent Application J 61100548 which claims 4-substituted benzyl 4-alkylcyclohexylacetates. Similar compounds with a O-CF₃ wing group are known from International Patent Application WO 89-02884. 4-(trans-4-Alkylcyclohexylmethoxy)-fluorobenzenes and 4-(trans,trans-4'-alkylbicyclohexyl-4-yl-methoxy)-3-fluorobenzonitriles are known from Japanese Patent Application J 60013731. EP-A-0344577 which is prior art under Article 54 (3) EPC discloses compounds of formulae with X being F, Cl or -NCS, and with m being 1 or 2 and L¹ being H or F, which are excluded from claims 10 and 11 by the proviso clauses a), b) and c). It has now been found that compounds of formulae I, II, III, IV, V and VI are highly suitable as components of liquid crystalline compositions for the use in twisted nematic cells. In particular, they have especially advantageous values of optical and dielectric anisotropy. It is also possible to obtain stable liquid crystalline phases with a broad nematic mesophase range and a comparatively low viscosity with the aid of these compounds. Depending on the choice of the substituents, the compounds of the formulae I, II, III, IV, V and VI can be used as the base materials from which liquid crystal media are predominantly composed; however, it is also possible for compounds of the formulae I, II, III, IV, V and VI to be added to liquid crystal base materials of other classes of compounds, for example in order to influence the dielectric and/or optical anisotropy and/or the viscosity and/or the mesophase range of such a dielectric. The compounds of the formulae I, II, III, IV, V and VI are colourless in the pure state and are liquid crystalline in a temperature range which is favourably placed for electrooptical use. They are very stable towards chemicals, heat and light. The invention thus relates to a liquid crystalline composition for the use in a twisted nematic cell being an admixture of a group (A) with one or more components exhibiting a positive dielectric anisotropy (Δε) and a group (B) with one or more components exhibiting a neutral dielectric anisotropy characterized in that (a) at least one component of group (A) is a compound of the formula I, II, III or IV or (b) at least one component of group (B) is a compound of the formula V or VI. In particular to liquid crystalline compositions wherein the dielectric anisotropy (Δε) of the group A is greater than +6 or wherein the dielectric anisotropy (Δε) of the group B is -4 to +3. Furthermore, the invention relates to a twisted nematic cell containing a liquid crystalline composition according to the invention in particular to a cell in which the twist angle is between 160 and 300°. Some of the compounds of the formulae I, II, III, IV, V and VI are known, but some are still novel. Therefore, the invention relates to the novel compounds of the formulae I, II, III and IV, in particular to the compounds of the formulae III and IV. The compounds of the formulae I, II, V and VI, wherein E¹ is -CH₂CH₂- are particularly preferred. The compounds of the formula III wherein E² is -(CH₂) n - with n being 1, 2 or 3 are particularly preferred. Above and below, R¹, R², Y, X, Y¹, Z, Y², Z¹, Q, m, n, o and r have the meaning given unless expressly indicated otherwise. The laterally fluorinated compounds with a positive dielectric anisotropie of the formula I include compounds with two and three rings of the formulae Ia to Ih wherein alkyl denotes an alkyl residue with up to 16 C atoms. The non-fluorinated 3-cyclohexylpropylethers of the formula II include compounds with two and three rings of the formulae IIa to IId The compounds of the formulae III include compounds with two rings of the formulae IIIa to IIIl: wherein R¹ and Y¹ have the meaning given for formula III of claim 1, and p is 0 or 1, with the proviso that a) the compounds of formula IIIj, wherein Y¹ is F, Cl or NCS, are excluded, and b) the compounds of formula IIIk, wherein Y¹ is F are excluded. and compounds with three rings of formulae IIIm to IIIu: wherein R¹ and Y¹ have the meaning given for formula III of claim 1, with the proviso that c) the compounds of formula IIIs and IIIt, wherein Y¹ is F, are excluded. Furthermore, the invention relates to a liquid crystalline medium being a mixture of at least two compounds, characterized in that at least one compound is a cyclohexane derivative of the formula III. In the compounds of the part formulae IIIg to IIIu Y¹ denotes preferably F, Cl, CF₃ or Op-CF₃, in particular or O-CF₃. The compounds of the formulae IV include the preferred compounds of the formulae IVa to IVi with two rings: and with three rings of the formulae IVj to IVv: The compounds of the formulae IV, wherein r is 0, 1, 2 or 3 are preferred in particular wherein r is 0 or 1. Furthermore the invention relates to a liquid crystalline medium being a mixture of at least two components characterized in that at least one component is a compound of the formula IV. The laterally fluorinated compounds with a neutral dielectric anisotropie fo the formulae V include compounds with two and three rings of the formulae Va to Vd wherein p is 0 or 1. The neutral non-fluorinated 3-cyclohexylpropylethers of the formula VI include compounds with two and three rings of the formulae VIa and VIb. wherein p is 0 or 1. Laterally fluorinated compounds, however, are especially preferred because they generally exhibit a comperatively low viscosity. R¹ and/or R² are independently from each other alkyl, alkoxy, oxaalkyl, thioalkyl, alkorycarbonyl, alkanoyloxy or alkenyl and both can exhibit a straight-chain or branched structure. The compounds of the formulae IV, V and VI wherein the wing groups R1 and R2 each have more than 4-C atoms are particularly preferred as components of chiral tilted smectic liquid crystalline compositions. Alkyl or alkoxy preferably are straight-chain and have 2, 3, 4, 5, 6 or 7 C atoms. Accordingly they are preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, also methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy. Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxy∼ methyl), 2-(= ethoxymethyl) or 3-oxybutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4- 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8-, or 9-oxadecyl. Alkenyl is preferably straight-chain and has 2 or 10 C atoms. It is accordingly, in particular, vinyl, prop-1- or prop-2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5- -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl. Compounds of the formulae I, II, III and IV containing a branched terminal group can occasionally be of importance because of an improved solubility in the customary liquid crystal base materials. Compounds of the formulae I and II with a branched terminal group R¹ can be used as chiral doping substances if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials. Branched groups of this type as a rule contain not more than one chain branching. Preferred branched radicals are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl, 2-methylbutyl, isopentyl, (= 3-methylbutyl), 2-methylpentyl, 2-ethylhexyl, 2-propylpentyl, 2-octyl, isopropoxy, 2-methyl propoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 2-methylhexoxy, 1-methylhexoxy, 1-methylheptoxy (= 2-octyloxy), 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methyloctoxy, 6-methyloctanoyloxy, 4-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3-methylvaleryloxy, 4-methylhexanoyloxy, 2-methyl-3-oxapentyl and 2-methyl-3-oxahexyl. In the case of compounds with branched terminal group, formulae I, II, III, IV, V and VI include both the optical antipodes and racemates as well as mixtures thereof. In the following smaller groups A to K of preferred compounds of the formula III and the part formulae thereof alkyl denotes preferably normal alkyl group with 2 to 8 C atoms, Cyc is a 1,4-cyclohexylene group, Phe is a 1,4-phenylene group, PheF is a group of the formula and PhFF a group of the formula A) alkyl-Cyc-CH₂O-Phe-OCF₃ alkyl-Cyc-CH₂O-Phe-CF₃ alkyl-Cyc-CH₂O-Phe-OCF₂H alkyl-Cyc-CH₂O-PheF-OCF₃ alkyl-Cyc-CH₂O-PheF-CF₃ alkyl-Cyc-CH₂O-PheF-OCF₂H alkyl-Cyc-CH₂O-PhFF-OCF₃ alkyl-Cyc-CH₂O-PhFF-CF₃ alkyl-Cyc-CH₂O-PhFF-OCF₂H B) alkyl-Cyc-CH₂CH₂-CO-O-Phe-OCF₃ alkyl-Cyc-CH₂CH₂-CO-O-Phe-CF₃ alkyl-Cyc-CH₂CH₂-CO-O-Phe-OCF₂H alkyl-Cyc-CH₂CH₂-CO-O-Phe-F alkyl-Cyc-CH₂CH₂-CO-O-Phe-NCF alkyl-Cyc-CH₂CH₂-CO-O-Phe-Cl C) alkyl-Cyc-CH₂CH₂-COO-PheF-OCF₃ alkyl-Cyc-CH₂CH₂-COO-PheF-CF₃ alkyl-Cyc-CH₂CH₂-COO-PheF-OCF₂H alkyl-Cyc-CH₂CH₂-COO-PheF-F alkyl-Cyc-CH₂CH₂-COO-PheF-NCS alkyl-Cyc-CH₂CH₂-COO-PheF-Cl D) alkyl-Cyc-CH₂CH₂-COO-PhFF-OCF₃ alkyl-Cyc-CH₂CH₂-COO-PhFF-CF₃ alkyl-Cyc-CH₂CH₂-COO-PhFF-OCF₂H alkyl-Cyc-CH₂CH₂-COO-PhFF-F alkyl-Cyc-CH₂CH₂-COO-PhFF-NCS alkyl-Cyc-CH₂CH₂-COO-PhFF-Cl E) alkyl-Cyc-CH₂CH₂CH₂-O-Phe-OCF₃ alkyl-Cyc-CH₂CH₂CH₂-O-Phe-CF₃ alkyl-Cyc-CH₂CH₂CH₂-O-Phe-F alkyl-Cyc-CH₂CH₂CH₂-O-Phe-NCS alkyl-Cyc-CH₂CH₂CH₂-O-Phe-Cl F) alkyl-Cyc-CH₂CH₂CH₂-O-PheF-OCF₃ alkyl -Cyc-CH₂CH₂CH₂-O-PheF-CF₃ alkyl-Cyc-CH₂CH₂CH₂-O-PheF-F alkyl-Cyc-CH₂CH₂CH₂-O-PheF-NCS alkyl-Cyc-CH₂CH₂CH₂-O-PheF-Cl G) alkyl-Cyc-CH₂CH₂CH₂-O-PhFF-OCF₃ alkyl-Cyc-CH₂CH₂CH₂-O-PhFF-CF₃ alkyl-Cyc-CH₂CH₂CH₂-O-PhFF-F alkyl-Cyc-CH₂CH₂CH₂-O-PhFF-NCS alkyl-Cyc-CH₂CH₂CH₂-O-PhFF-Cl H) alkyl-Cyc-Cyc-CH₂O-Phe-OCF₃ alkyl-Cyc-Cyc-CH₂O-Phe-CF₃ alkyl-Cyc-Cyc-CH₂O-Phe-F alkyl-Cyc-Cyc-CH₂O-PheF-OCF₃ alkyl-Cyc-Cyc-CH₂O-PheF-CF₃ alkyl-Cyc-Cyc-CH₂O-PheF-F alkyl-Cyc-Cyc-CH₂O-PheF-NCS alkyl-Cyc-Cyc-CH₂O-PheF-Cl alkyl-Cyc-Cyc-CH₂O-PhFF-OCF₃ alkyl-Cyc-Cyc-CH₂O-PhFF-CF₃ alkyl-Cyc-Cyc-CH₂O-PhFF-F alkyl-Cyc-Cyc-CH₂O-PhFF-Cl alkyl-Cyc-Cyc-CH₂O-PhFF-NCS I) alkyl-Cyc-Cyc-CH₂CH₂-CO-O-Phe-OCF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-Phe-CF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-Phe-F alkyl-Cyc-Cyc-CH₂CH₂-CO-O-Phe-Cl alkyl-Cyc-Cyc-CH₂CH₂-CO-O-Phe-NCS J) alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PheF-OCF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PheF-CF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PheF-F alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PheF-Cl alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PheF-NCS K) alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PhFF-OCF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PhFF-CF₃ alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PhFF-F alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PhFF-Cl alkyl-Cyc-Cyc-CH₂CH₂-CO-O-PhFF-NCS The compounds of the formulae I to VI are prepared by methods which are known per se, such as are described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), and in particular under reaction conditions which are known and suitable for the reactions mentioned in more detail here can also be used in this connection. If desired, the starting substances can also be formed in situ, such that they are not isolated from the reaction mixture but are immediately reacted further to give the compounds of the formulae I to VI. Esters of the formulae I to V can be obtained by esterification of corresponding carboxylic acids (or their reactive derivatives) with alcohols or phenols (or their reactive derivatives) preferably the corresponding carboxylic acid and the alcohol or phenol are reacted with water absorbing means as, for example, mol sieves or carbodiimides, particularly preferably with dicyclohexylcarbodiimide . The corresponding carboxylic acids of the formula VIIa and phenols of the formula VIIIa to VIIIe are known or can be prepared by processes analogous to known processes. Particularly suitable reactive derivatives of the carboxylic acids mentioned are the acid halides, above all the chlorides and bromides, and furthermore the anhydrides, for example also mixed anhydrides, preferably those of the corresponding carboxylic acids and trifluoroacetic acid formed in situ by mixing these carboxylic acids with trifluoroacetic anhydride, azides or esters, in particular alkyl esters with 1-4 C atoms in the alkyl group. Possible reactive derivatives of the alcohols or phenols mentioned are, in particular, the corresponding metal alcoholates or phenolates, preferably of an alkali metal, such as sodium or potassium. The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable solvents are ethers, such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones, such as acetone, butanone or cyclohexanone, amides, such as dimethylformamide or phosphoric acid hexamethyltriamide, hydrocarbons, such as benzene, toluene or xylene, halogenohydrocarbons, such as carbon tetrachloride, dichlormethane or tetrachloroethylene, and sulfoxides, such as dimethylsulfoxide or sulfolane. Water-immiscible solvents can simultaneously be advantageously used for azeotropic distillation of the water formed during the esterification. An excess of an organic base, for example pyridine, quinoline or triethylamine, can occasionally also be used as the solvent for the esterification. An additional, catalytic amount of 4-(N,N-dimethylamino)-pyridine can accelerate the esterification. The esterification can also be carried out in the absence of a solvent, for example by heating the components in the presence of sodium acetate. The reaction temperature is usually between -50° and +250°, preferable between -20° and +80°. At these temperatures, the esterification reactions have as a rule ended after 15 minutes to 48 hours. In detail, the reaction conditions for the esterification depend largely on the nature of the starting substances used. Thus, a free carboxylic acid is as a rule reacted with a free alcohol or phenol in the presence of a strong acid, for example a mineral acid, such as hydrochloric acid or sulfuric acid. A preferred reaction procedure is the reaction of an acid anhydride or, in particular, an acid chloride with an alcohol, preferably in a basic medium, bases which are of importance being, in particular, alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal carbonates or bicarbonates, such as sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate, alkali metal acetates, such as sodium acetate or potassium acetate, alkaline earth metal hydroxides, such as calcium hydroxide, or organic bases, such as triethylamine, pyridine, lutidine, collidine or quinoline. Another preferred embodiment of the esterification comprises first converting the alcohol or phenol into the sodium alcoholate or phenolate or potassium alcoholate or phenolate, for example by treatment with ethanolic sodium hydroxide solution or potassium hydroxide solution, isolating this product and suspending it in acetone or diethyl ether, together with sodium bicarbonate or potassium carbonate, with stirring, and adding a solution of the acid chloride or anhydride in diethyl ether, acetone or diemthylformamide to this suspension, advantageously at temperatures between about -25° and +20°. Alkoxy compounds of the formula III (o = O) can be obtained by alkylation of the corresponding phenols of the formula VIIIe, the phenol preferably first being converted into a phenolate for example into the alkali metal phenolate by treatment with NaOH, KOH, Na₂CO₃ or K₂CO₃. This phenolate can then be reacted with the corresponding reactive derivative of the alcohols of the formula VIIb in an inert solvent such as acetone, DMF or dimethylsulfoxide or an excess of aqueous or aqueous alcoholic NaOH or KOH at temperatures between 0° and 100 °C. Reactive derivatives of the alcohols of the formula VIIb are preferably the sulfonates as for example toluene sulfonate or mesilated. The alcohol of the formula VIIb and the corresponding phenol can also be treated with triphenyl phosphine and diethyl azodicarboxylate as described by O. Mitsunobu, Synthesis 1981 , 1. The 3-cyclohexylpropanols (n = 3) of the formula VIIb can be obtained by reduction of VIIa (n = 2) with, for example, lithium alanate. The compounds of the formula IV can be obtained according to the following schemes: The compounds of the formulae I, II, III, V and VI wherein the bridging group is an allylic ether of the formula -CH=CH-CH₂-O- can be obtained according to scheme 3 The compounds of the formulae I, III and V wherein the bridging groups is an acrylic acid ester can be obtained according to scheme 4. The compounds of the formula III, wherein E² is (CH₂)₃, o is O and Y¹ is OCF₂H, can be obtained according to scheme 5 The compounds of the formula III, wherein E₂ is (CH₂)₃, o is O and Y₁ is CF₃ can be obtained according to scheme 6 In addition to one or more compounds of formulae I to VI the liquid crystal compositions according to the invention preferably contain 2-40 components and in particular 4-30 components. Liquid crystal compositions being composed of one or more compounds of formulae I, II, III, IV, V and VI and 7-25 other components are especially preferred. These additional components are preferably chosen from the nematic or nematogenic (monotropic or isotropic) substances; in particular from the classes of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenyl or cyclohexyl cyclohexylbenzoates, phenyl or cyclohexyl cyclohexylcyclohexanecarboxylates, cyclohexylphenylbenzoates, cyclohexylphenyl cyclohexanecarboxylates, cyclohexylphenyl cyclohexylcyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexene, 1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenyl-cyclohexyl)-ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolanes and substituted cinnamic acids. The 1,4-phenylene groups of these compounds may be fluorinated. The most important compounds which are possible constituents of liquid crystal compositions according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5: R′-L-U-R″ R′-L-COO-U-R″ R′-L-OOC-U-R″ R′-L-CH₂CH₂-U-R″ R′-L-C≡C-U-R″ In the formulae 1, 2, 3, 4 and 5 L and U may be equal or different from each other. L and U independently from each other denote a bivalent residue selected from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe-, -G-Cyc- and their mirror images; in this compilation of residues Phe denotes unsubstituted or fluorinated 1,4-phenylen, Cyc trans- 1,4-cyclohexylene or 1,4-cyclohexenylen, Pyr pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio 1,3-dioxane-2,5-diyl and G 2-(trans-1,4-cyclohexyl)-ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl. One of the residues L and U is preferably Cyc, Phe or Pyr. U preferably denotes Cyc, Phe or Phe-Cyc. The liquid crystal media according to the invention preferably contain one or more components selected from the compounds of formulae 1, 2, 3, 4 and 5 with L and U meaning Cyc, Phe and Pyr, said liquid crystal media further containing at the same time one or more components selected from the compounds of formulae 1, 2, 3, 4 and 5 with one of the residues L and U denoting Cyc, Phe and Pyr and the other residue being selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Cyc-, said liquid crystal media containing in addition to this optionally one or more components selected from the compounds of formulae 1, 2, 3, 4 and 5 with L and U being selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc. In a preferred subgroup of the compounds of formulae 1, 2, 3, 4 and 5 (subgroup 1) R′ and R″ are independently from each other alkyl, alkenyl, alkoxy, alkenoxy with up to 8 carbon atoms. R′ and R″ differ from one another in most of these compounds, one of the residues usually being alkyl or alkenyl. In another preferred subgroup of the compounds of formulae 1, 2, 3, 4 and 5 (subgroup 2) R″ denotes -CN, -CF3, -F, -Cl or -NCS while R′ has the meaning indicated in subgroup 1 and is preferably alkyl or alkenyl. Other variants of the envisaged substituents in the compounds of formulae 1, 2, 3, 4 and 5 are also customary. Many such substances are commercially available. All these substances are obtainable by methods which are known from the literature or by analogous methods. The liquid crystal compositions according to the invention preferably contain in addition to components selected from subgroup 1 also components of subgroup 2, the percentage of these components being as follows: subgroup 1: 20 to 90 %, in particular 30 to 90 % subgroup 2: 10 to 50 %, in particular 10 to 50 % In these liquid crystal media the percentages of the compounds according to the invention and the compounds of subgroup 1 and 2 may add up to give 100 %. The compositions according to the invention preferably contain 1 to 40 %, in particular 5 to 30 % of the compounds according to the invention. Media containing more than 40 %, in particular 45 to 90 % of the compounds according to the invention are further preferred. The media contain preferably 3, 4 or 5 compounds according to the invention. The compositions according to the invention are prepared in a manner which is customary per se. As a rule, the components are dissolved in one another, advantageously at elevated temperature. The liquid crystal compositions according to the invention can be modified by suitable additives so that they can be used in all the types of liquid crystal display devices. Such additives are known to the expert and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, it is possible to add pleochroic dyestuffs to prepare colored guest-host systems or substances for modifying the dielectric anisotropy, the viscosity and/or the orientation of the nematic phases. Preferably the compositions according to the invention are used in twisted nematic cells. Twisted nematic cells includes all types of displays, which are based on twisted nematic effect in particular the TN-LCD, the supertwisted STN- and OMI-LCDs, cells which are addressed by a thin film transistor (TFT-LCD) and the SBE-cells. The following examples are to be construed as merely illustrative and not limitative. m.p. = melting point, c.p. = clearing point. In the foregoing and in the following all parts and percentages are by weight and the temperatures are set forth in degrees Celsius. "Customary work-up" means that water is added, the mixture is extracted with methylene chloride, the organic phase is seperated off, dried and evaporated, and the product is purified by crystallization and/or chromatography. Further are: C: crystalline-solid state, S: smectic phase (the index denoting the typ of smectic phase), N: nematic phase, Ch: cholesteric phase, I: isotropic phase. The number being embraced by 2 of these symbols denotes the temperature of phase change. Example 1 Step 1: Preparation of 3-(trans-4-propylcyclohexyl)-propionic acid Trans 4-propyl cyclohexyl methane tosylate (100 g) is dissolved in dry methylated spirits (500 ml) and slowly added to a suspension of sodio diethyl malonate prepared from sodium (7.42 g) and diethyl malonate (54.2 g) in dry ethanol (210 ml). The mixture is heated and stirred for 30 hours. After distilling off the ethanol, the mixture is extracted into ether (3 x 200 ml), washed with water and dried. After evaporation of the solvent the diester product solidifies. Yield 59 g Mpt 47 °C. The diester (59 g) is refluxed for 2 hours with KOH (59 g), water (60 ml) and ethanol (200 ml), about 160 ml of ethanol is distilled off and water (60 ml) added. When cool, conc. H2SO4 (51 m) in water (130 ml) is added and the mixture is heated for 2 hours. After cooling the mixture is extracted with ether which after the usual workup gave the desired acid. Step 2: Ester Synthesis A mixture of the acid from Step 1 (0.023 m), 4-cyano-3-fluorophenol (0.034 m) and dicyclohexylcarbodiimide (0.025 m) in dichloromethane (180 ml) is stirred for 16 hours. The mixture is filtered, evaporated to dryness, chromatographed and crystallized to yield (4-cyano-3-fluorophenyl) 3-(trans-4-propylcyclohexyl)-propionate K 46.5 N (-8.7) I. Analogously are obtained: (4-cyano-3-fluorophenyl) 3-(trans-4-ethylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans-4-butylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans-4-pentylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans-4-hexylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans-4-heptylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans-4-octylcyclohexyl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-butylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-hexylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl-4-yl)-propionate (4-cyano-3-fluorophenyl) 3-(trans,trans-4′-octylbicyclohexyl-4-yl)-propionate (3,4-difluorophenyl) 3-(trans-4-ethylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-propylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-butylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-pentylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-hexylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-heptylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans-4-octylcyclohexyl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl-4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl-4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-butylbicyclohexyl4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-hexylbicyclohexyl-4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl-4-yl)-propionate (3,4-difluorophenyl) 3-(trans,trans-4′-octylbicyclohexyl-4-yl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-ethylcyclohexyl)-propionate K 43.6 N (-27) I (4-chloro-3-fluorophenyl) 3-(trans-4-propylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-butylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-pentylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-hexylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-heptylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans-4-octylcyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-butylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-hexylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl)-propionate (4-chloro-3-fluorophenyl) 3-(trans,trans-4′-octylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-butylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-hexylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl)-propionate (4-fluorophenyl) 3-(trans,trans-4′-octylbicyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-ethylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-propylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-butylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-pentylcycloheryl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-hexylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-heptylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans-4-octylcyclohexyl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-butylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-hexylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl-4-yl)-propionate (4-propyl-3-fluorophenyl) 3-(trans,trans-4′-octylbicyclohexyl-4-yl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,4-propylcyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,4-propylcyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,4-propylcyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,4-pentylcyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,4-pentylcyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,4-pentylcyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,4-heptylcyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,4-heptylcyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,4-heptylcyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,4-octylcyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,4-octylcyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,4-octylcyclohexyl)-propionate (4-propyloxy-3-fluorophenyl) 3-(trans,4-pentylcyclohexyl)-propionate (4-pentyloxy-3-fluorophenyl) 3-(trans,4-pentylcyclohexyl)-propionate (4-heptyloxy-3-fluorophenyl) 3-(trans,4-propylcyclohexyl)-propionate (4-octyloxy-3-fluorophenyl) 3-(trans,4-propylcyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl) -propionate (4-octyl-3-fluorophenyl) 3-(trans,trans-4′-propylbicyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-pentyl-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl)-propionate (4-heptyl-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl)-propionate (4-octyl-3-fluorophenyl) 3-(trans,trans-4′-heptylbicyclohexyl)-propionate (4-propyloxy-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-pentyloxy-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate (4-heptyloxy-3-fluorophenyl) 3-(trans,trans-4′-pentylbicyclohexyl)-propionate Example 2 Step 1: Preparation of 3-(trans-5-propylcyclohexyl)-1-propanole The methyl ester (0.2 m) of the acid of Example 1 Step 1 is dissolved in dry ether (150 ml) and slowly added to a stirred and cooled mixture of LiAlH₄ (0.12 m) in dry ether (100 ml). After complete addition to mixture is stirred for 16 hours at 20 °C and then heated to reflux for 1 hour. After cooling, ethyl acetate followed by water and dilute H₂SO₄ are added. The organic layer is separated and the product isolated. Vacuum distillation affords the pure product. Step 2: Synthesis of the Tosylate A mixture of alcohol of Step 1 (0.1 m) and toluenesulphonyl chloride (0.1 m) is dissolved in pyridine and dichloromethane and the mixture stirred for 16 hours. The mixture is then repeatedly extracted with cold dilute hydrochloric acid. After drying and evaporation the tosylate is isolated. Step 3: Etherification A mixture of tosylate of step 2 (0.1 m), p-pentyl phenol (0.1 m), potassium carbonate (0.2 m) and butanone (200 ml) is stirred and refluxed for 12 hours. Solid is filtered off, butanone evaporated and the product purified by chromatography/crystallisation to yield 1-(trans-4-propylcyclohexyl)-3-(p-pentylphenyloxy)-propane. Analogously are obtained 1-(trans-4-ethylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-butylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-hexylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-heptylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-octylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-nonylcyclohexyl)-3-(p-pentylphenyloxy)-propane 1-(trans-4-ethylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-propylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-hexylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-heptylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-octylcyclohexyl)-3-(p-heptylphenyloxy)-propane 1-(trans-4-ethylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-propylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-butylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane K 42 S A 48 N 53 I 1-(trans-4-hexylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-heptylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-octylcyclohexyl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-pentylphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-heptylphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-octylphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-pentyloxyphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-heptyloxyphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-octyloxyphenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-cyanophenyloxy)-propane K 59 N (29) I 1-(trans-4-pentylcyclohexyl)-3-(3-fluoro-4-chlorophenyloxy)-propane 1-(trans-4-pentylcyclohexyl)-3-(3,4-difluorophenyloxy)-propane K 4 I 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(p-pentylphenyl-oxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(p-heptylphenyloxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(p-pentyloxyphenyloxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(3-fluoro-4-pentylphenyloxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(3-fluoro-4-cyanophenyloxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(3-fluoro-4-chlorophenyloxy)-propane 1-(trans,trans-4′-pentylbicyclohexyl-4-yl)-3-(3,4-difluorophenyloxy)-propane Example 3 A mixture of 0.1 mol trans-4-n-pentylcyclohexylmethyl toluene sulfonate (obtainable by reduction of trans-4-n-pentylcyclohexane carboxylic acid with lithium alonate and esterification with toluene sulfonyl chloride), 0.1 mol trifluoromethoxy phenol, 0.1 mol potassium carbonate and 100 ml of dimethylformamide is heated to 100 °C for 15 hours. After destilling off the major part of the solvent water is added to the residue. After the aqueous layer is extracted with dichloromethane the organic layer is washed with water, dried with magnesium sulfate and the solvent is evaporated. 0.083 mol of 1-(trans-4-n-pentylcycloheryl)-methoxy-4-trifluormethoxy benzene are obtained. Analogously are obtained: 1-(trans-4-ethylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans-4-n-propylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans-4-n-butylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans-4-n-hexylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans-4-n-heptylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans-4-n-octylcyclohexyl)-methoxy-4-trifluomethoxybenzene 1-(trans,trans-4′-ethylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-propylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-butylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-pentylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-hexylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-heptylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-octylbicyclohexyl-4-yl)-methoxy-4-trifluoromethoxybenzene 1-(trans-4-ethylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-propylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-pentylcyclohexyl)methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-pentylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-hexylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-heptylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans-4-n-octylcyclohexyl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-ethylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-propylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-butylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-pentylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-hexylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-heptylbicyclohexyl-4-yl)methoxy-3-fluoro-4-trifluoromethoxybenzene 1-(trans,trans-4′-n-octylbicyclohexyl-4-yl)-methoxy-3-fluoro-4-trifluoromethoxybenzene Example 4 A stream of ammonia is bubbled through a solution of 4-[trans-4-(trans-4-n-pentylcyclohexyl)-cyclohexyl-]methoxyanilin (0.01 mol, obtained by reaction of [trans-4-(trans-4-(trans-4-n-pentyl-cyclohexyl)-cyclohexyl]-methyl-toluenesulfonate with 4-acetamidophenol in the presence of potassium carbonate and dimethylformamide followed by the saponification of the acetanilide) for 10 minutes . 0.8 g of CS₂ are added and the ammonia is bubbled through until saturation. A solution of phosgene in toluene (6 ml, 20 %) is added and stirred for 30 minutes. After filtration evaporation and crystallization 4-[trans-4-(4-n-pentylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate are obtained. Analogously are obtained: 4-[trans-4-(trans-4-ethylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-n-propylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-n-butylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-n-hexylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-n-heptylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-n-octylcyclohexyl)-cyclohexyl]-methoxyphenylisothiocyanate 4-[trans-4-(trans-4-ethylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-propylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-butylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-pentylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-hexylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-heptylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-[trans-4-(trans-4-n-octylcyclohexyl)-cyclohexyl]-methoxy-2-fluorophenylisothiocyanate 4-trans-4-trans-4-ethylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-propylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-butylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-pentylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-hexylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-heptylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate 4-trans-4-trans-4-n-octylcyclohexyl)-cyclohexyl-methoxy-2,6-difluorophenylisothiocyanate Example 4 A solution of dicyclohexylcarbodiimide (0.01 mol) in dichloromethane (15 ml) is added to a mixture of 3-[trans-4-(trans-4-n-pentylcyclohexyl)-cyclohexyl]-propionic acid (0.001 mol, obtained from 4-trans-(trans-4-n-pentylcyclohexyl)-cyclohexane carboxylchloride via Rosemund-reduction to the corresponding aldehyde, Knoevenagel-condensation with malonic acid and hydrogenation of double bond), 4-dimethylaminopyridine (0,001 mol), 4-trifluoromethylphenol (0.01 mol) and dichloromethane (15 ml) at 10 °C under stirring. The mixture is stirred at room temperature for 15 hours. After filtration from silic gel the solvent is evaporated. (4-Trifluoromethylphenyl) 3-[trans-4-(trans-4-n-pentylcyclohexyl)-cyclohexyl]-propionate are obtained. Analogously are obtained: (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-ethylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-n-propylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-n-butylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-n-hexylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-n-heptylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-[trans-4-(trans-4-n-octylcyclohexyl)-cyclohexyl]-propionate (4-trifluoromethylphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-propylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-butylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-pentylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-hexylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-heptylcyclohexyl)-propionate (4-trifluoromethylphenyl) 3-(trans-4-n-octylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-propylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-butylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-pentylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-hexylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-heptylcyclohexyl)-propionate (4-trifluoromethoxyphenyl) 3-(trans-4-n-octylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-propylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-butylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-pentylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-hexylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-heptylcyclohexyl)-propionate (4-difluoromethoxyphenyl) 3-(trans-4-n-octylcyclohexyl)propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-propylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-butylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-pentylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-hexylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-heptylcyclohexyl)-propionate (3-fluoro-4-trifluoromethylphenyl) 3-(trans-4-n-octylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-propylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-butylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-pentylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-hexylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-heptylcyclohexyl)-propionate (3,4,5-trifluorphenyl) 3-(trans-4-octylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-ethylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-propylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-butylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-pentylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-hexylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-heptylcyclohexyl)-propionate (3,5-difluoro-4-trifluoromethylphenyl) 3-(trans-4-n-octylcyclohexyl)-propionate (3,4,5-trifluorophenyl) 3-(trans,trans-4′-ethylbicyclohexyl)-propionate (3,4,5-trifluorophenyl) 3-(trans,trans-4′-n-propylbicyclohexyl)-propionate (3,4,5-trifluorophenyl) 3-(trans,trans-4′-n-butylbicyclohexyl)-propionate (3,4,5-trifluorophenyl) 3-(trans,trans-4′-n-pentylbicyclohexyl)-propionate (3,4,5-trifluorophenyl) 3-(trans,trans-4′-n-octylbicyclohexyl)-propionate Example 6 A mixture of 3-[trans-4-(trans-4-n-pentylcyclhexyl)-cyclohexyl]-propyl-toluenesulfonate (0.1 mol, obtained from the acid described in example 4 by reduction with lithium alanate and esterification with p-toluenesulfonylchloride), 4-fluorophenol (0.1 mol), potassium carbonate (0.1 mol) and dimethylformamide (100 ml) are heated to 100 °C for 15 hours. After work-up as described in example 1 4-{3-[trans-4-(trans-4-n-pentylcyclohexyl)-cyclohexyl]-propyloxy}-fluorobenzene are obtained. Analogously are obtained: Example 7 Preparation of 4-(trans,trans-4′-pentylbicyclohexyl-4-yl-methoxy)-2-fluoro-chlorobenzene trans-trans-4-pentylbicyclohexyl methyl iodide (0.02 m) is heated under reflux and stirred with butanone (200 ml) potassium carbonate (0.04 m) and 4-chloro 3-fluorophenol (0.021 m) for 16 hours. The mixture filtered and evaporated to dryness. The product is purified by column chromatography and crystallisation from ethanol and shows K 87 N 137.9 I. Analogously are obtained Example 8 A mixture of 3-(trans-4-propylcyclohexyl)-propyl-toluenesulfonate (0.1 mol, cp. Example 6), 3,5-difluorophenol (0.1 mol), potassium carbonate (0.1 mol) and dimethylformamide (10 ml) are heated to 100 °C for 15 hours. 62 ml of n-Buli (15 % in hexane) are added to a mixture of the obtained compound (90 mmol/l / cp. Scheme 6), TMEDA (100 mmol) and 100 ml THF at -70 °C. After 1 hour of stirring at -70 °C a solution of iodine (94 mmol) in 50 ml THF is added and 0.5 hrs stirred. After warning up to -30 °C 30 ml water and 30 ml of a dilute solution of sodium hydrogen sulfite are added. After costumary work-up 4-[3-(trans-4-propylcyclohexyl)-propyloxy]-2,6-difluoro-iodobenzene are obtained. A mixture of this iodobenzene derivative (76 mmol), potassium fluoride (152 mmol), sodium trifluoroacetate (336 mmol) and 1600 ml N-methylpyrolidone (NMP) are heated to 70 °C and 800 ml of NMP are distilled off at 4 mbar. CuI (152 mmol) is added to the reaction mixture and stirred for 5 hours at 160 °C. Then 800 ml NMP are distilled off. After the mixture is cooled to room temperature, 800 ml methyl-tert.-butylether are added. After customary work-up 4-[3-trans-4-propylcyclohexy)-propyloxy]-2,6-difluorotrifluoromethylbenzene are obtained. Analogously are obtained: Example 9 A mixture of 4-[3-(trans-4-Pentylcyclohexyl)-propyloxy]-2-fluoro-phenol (10 mmol/obtained from 3-(trans-4-pentylcyclohexyl)-propyl-toluene sulfonate and 4-benzyloxy-3-fluorophenol as described in Example 6 followed by hydrogenolytic clearage of the benzylic ether), 50 ml THF, an aqueous solution of sodium hydroxide (32 %, 3.1 g) and tetrabutylammoniumhydrogen sulfate (0.5 g) is heated to 50 °C. Chlorodifluoromethane is added until it condenses on a condenser that is cooled by dry-ice. After costumary work-up 4-[3-(trans-4-pentylcyclohexyl)-propyloxy]-2-fluorodifluoromethoxybenzene are obtained. Analogously are obtained:

Claims: A nematic liquid crystalline composition comprising a group (A) with one or more components exhibiting a positive dielectric anisotropy (Δε) and a group (B) with one or more components exhibiting a neutral dielectric anisotropy characterized in that (a) at least one component of group (A) is a compound of the formula I wherein R¹ is an alkyl or alkenyl residue each with up to 16 C atoms, wherein one or two non-adjacent CH₂-groups of these residues may be replaced by -O-, -S-, -CO-O-, or -O-CO-, E¹ is -CH₂CH₂- or -CH=CH- Q is -CO- or -CH₂-, Y is halogen or CN, and m is 1 or 2 or a compound of the formula II wherein R¹, E¹, Y and m have the meaning given for formula I, or a compound of the formula III wherein R¹ is an alkyl or alkenyl residue each with up to 16 C atoms, wherein one or two non-adjacent CH₂-groups of these residues may be replaced by -O-, -S-, -CO-O-, or -O-CO, E² is -(CH₂) n - or CH=CH-(CH₂) n-2 - X and Z are each independently H or F, Y¹ is F, Cl, NCS, CF₃, OCF₃ or OCF₂H, m is 1 or 2, n is 1, 2 or 3, o is 0 or 1 with the proviso that m is 2 or n is 2 or 3 in the case that Y¹ is F, Cl or NCS, or a compound of the formula IV wherein R¹ and m have the meaning given for formula I, and Z¹ is -(CH₂)₄-, -(CH₂)₃-O- or -CH=CH-CH₂CH₂- Y² is CF₃, OCF₃ or -CH=CH-CF₃, and r is 0 to 7, or that (b) at least one component of group (B) is a compound of the formula V wherein R¹, E¹, Q and m have the meaning given for formula I, and R² is an alkyl or alkenyl residue with up to 16 C atoms wherein one or two non-adjacent CH₂ groups of these residues may be replaced by -O-, -S-, -CO-O- or -O-CO- or a compound of the formula VI wherein R¹, R², E¹ and m have the meaning given for formula V. A nematic liquid crystalline composition according to claim 1, characterized in that E¹ denotes -CH₂CH₂- in the compounds of the formulae I, II, V and VI and E² denotes -(CH₂) n -, in the compounds of the formula III. A liquid crystalline composition according to claim 2, characterized in that at least one component of group (A) is selected from the compounds of the formulae Ia to In wherein alkyl denotes an alkyl residue with up to 16 C atoms. A liquid crystalline composition according to claim 2 characterized in that at least one component of group (A) is selected from the compounds of the formulae IIa to IId: A liquid crystalline composition according to claim 2 characterized in that at least one component of the group (B) is selected from the compounds of the formulae Va to Vd or VIa to VIb wherein p is 0 or 1. A liquid crystalline composition according to at least one of the claims 1 to 5 characterized in that the dielectric anisotropy (Δε) of the group A is greater than +6. A liquid crystal composition according to at least one of the claims 1 to 6 characterized in that the dielectric anisotropy (Δε) of the group B is -4 to +3. A twisted nematic cell containing a liquid crystalline composition according to at least one of the claims 1 to 7. A cell according to claim 8 characterized in that the twist angle is between 160 and 300°. Cyclohexane derivatives of the formula III selected from the formula IIIa to IIIl wherein R¹ and Y¹ have the meaning given for formula III of claim 1, and p is 0 or 1, with the proviso that a) the compounds of formula IIIj, wherein Y¹ is F, Cl or NCS, are excluded, and b) the compounds of formula IIIk, wherein Y¹ is F are excluded. Cyclohexane derivatives of the formula III selected from the formulae IIIm to IIIu wherein R¹ and Y¹ have the meaning given for formula III of claim 1, with the proviso that c) the compounds of formula IIIs and IIIt, wherein Y¹ is F, are excluded. A liquid crystalline medium according to claim 1 being a mixture of at least two compounds, characterized in that at least one compound is a cyclohexane derivative of the formula III wherein R¹, E², X, Z, Y¹, m, n and o have the meaning given in claim 1. A liquid crystalline medium according to claim 1 being a mixture of at least two components, characterized in that at least one component is a compound of the formula IV wherein R¹, m, Z¹, Y² and r have the meaning given in claim 1.

Inventors: BARTMANN EKKEHARD DR, CLEMITSON ROBERT WILLIAM DR, COATES DAVID DR, DORSCH DIETER DR, GEELHAAR THOMAS DR, HITTICH REINHARD DR, KOMPTER HANS-MICHAEL DR, KRAUSE JOACHIM DR, KURMEIER HANS-ADOLF DR, PAULUTH DETLEF DR, POETSCH EIKE DR, BARTMANN, EKKEHARD, DR., CLEMITSON, ROBERT WILLIAM, DR., COATES, DAVID, DR., DORSCH, DIETER, DR., GEELHAAR, THOMAS, DR., HITTICH, REINHARD, DR., KOMPTER, HANS-MICHAEL, DR., KRAUSE, JOACHIM, DR., KURMEIER, HANS-ADOLF, DR., PAULUTH, DETLEF, DR., POETSCH, EIKE, DR.
Applicants: MERCK PATENT GMBH
Application year: 1990
Main classification: C09K19
IPC codes: C07C69, C09K19, C07C43, C07C255, C07C331