| 摘要 |
There is described compounds of the formula <IMAGE> I wherein X stands for CH and Y stands for N or X stands for N and Y stands for CH; A1 and A2 signify single covalent bonds or one of the groups A1 and A2 also signifies trans-1,4-cyclohexylene, cis-4-cyano-trans-1,4-cyclohexylene or 1,4-phenylene optionally substituted with halogen or methyl; ring B represents trans-1,4-cyclohexylene, 1,4-phenylene optionally substituted with halogen or methyl or, when A2 signifies a single covalent bond, also cis-4-cyano-trans-1,4-cyclohexylene; R1 denotes an optionally halogen-substituted alkyl or alkenyl group in which optionally one CH2 group or two non-adjacent CH2 groups is/are replaced by -O-, -COO- and/or -OOC-; R2 signifies an optionally halogen-substituted alkyl or alkenyl group in which optionally one CH2 group or two non-adjacent CH2 groups is/are replaced by -O-, -COO- and/or -OOC- or R2 on a benzene ring also signifies -NCS, cyano or halogen; with the proviso that R1 denotes an optionally halogen-substituted alkenyl group in which optionally one CH2 group or two non-adjacent CH2 groups is/are replaced by -O-, -COO- and/or -OOC- when R2 signifies cyano or halogen; and with the proviso that R1 and/or R2 has a chiral carbon atom when R1 and R2 stand for optionally halogen-substituted alkyl groups in which optionally one CH2 group or two non-adjacent CH2 groups is/are replaced by -O-, -COO- and/or -OOC-, as well as liquid crystalline mixtures and their use for electro-optical purposes.
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