| 摘要 |
Compounds of the formula <IMAGE> I wherein R1 is hydrogen or straight-chain alkyl; R2 is -CN, -R, -COR, -COOR or when R2 is positioned on an aromatic ring R2 also can be -OR, -OOCR or -F; R is alkyl; A is a group with 1 to 4 six-membered rings, these rings being linked directly with one another and with ring B in each case via a single covalent bond or being linked at one or two positions also via -COO-, -OOC- or -CH2CH2-; the six-membered rings in A and ring B each are 1,4-phenylene or trans-1,4-cyclohexylene or one of these rings also is trans-2,5-disubstituted m-dioxane, 2,5-disubstituted pyrimidine or 3,6-disubstituted pyridazine, with the proviso that a maximum of two adjacent trans-1,4-cyclohexylene rings are linked directly via a single covalent bond; and m is the integer 2, or when ring B is trans-1,4-cyclohexylene or trans-2,5-disubstituted m-dioxane, m also can be the integer 0, their manufacture, liquid crystalline mixtures which contain these compounds as well as the use of these compounds for electro-optical purposes are described. Additionally, compounds of the formula <IMAGE> LXXVIII wherein R8 is straight-chain C1-C12 alkyl, their manufacture, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes are described.
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