| 摘要 |
Compounds of the formula <IMAGE> I wherein X1 denotes fluorine or chlorine and X2 denotes hydrogen, fluorine or chlorine; R1 is 3E-alkenyl, 4-alkenyl, 2E-alkenyloxy or 3-alkenyloxy; n stands for the number 0 or 1; one of the groups Y1 and Y2 is a single covalent bond, -COO-, -OOC-, -CH2CH2-, -CH2O- or -OCH2- and the other of the groups Y1 and Y2 is a single covalent bond; and rings A1 and A2 each individually are substituted or unsubstituted trans-1,4-cyclohexylene, in which optionally 2 non-adjacent CH2 groups are replaced by oxygen, or substituted or unsubstituted 1,4-phenylene, in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen; with the proviso that X2 denotes fluorine or chlorine and/or Y1 or Y2 denotes -CH2O- or -OCH2- when simultaneously X1 is fluorine and R1 is 3E-alkenyl, and their use for liquid crystalline mixtures and electro-optical purposes.
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