| 摘要 |
A compound of formulain whichR1 and R2 each independently represent and alkyl or alkenyl group in which one or more hydrogen atoms is optionaly substituted by fluorine, chlorine, or cyano; and in which optionally one or more non-adjacent methylene groups are optionaly replaced by -O-, -COO- or -OOC-;Z1 to Z4 each independently represent a single bond, -CH2CH2-, -CH2O-, -OCH2-, -C=C-, -(CH2)4-, -(CH2)3O-, -CH=CH-CH2O-, OCH2-, -CH=CH-, -CH=CH-(CH2)2- or -(CH2)2-CH=CH-, with the proviso firstly that the oxygen atom is not linked directly with the chiral dioxane ring and secondly Z2 and Z3 may also represent -COO- or -OOC-;R* and S* signify that the denoted carbon have the (R) or (S) configuration respectively or the optical antipode thereof; andone of A, B and C is a 1,4-phenylene which is optionally substituted with 1 or 2 fluorine atoms, pyridine-2,5-diyl or pyrimidine-2,5-diyl and the other two rings are each independently 1,4-phenylene which is optionally substituted by one or more a fluorine atoms or trans-1,4-cyclohexylene;liquid crystalline mixtures containing said compounds and the use of said compounds for electro-optical purposes.
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