| abstract |
Optically active compounds of the formula <IMAGE> I wherein rings A1 and A2 each independently signify pyridine-2,5-diyl, pyrimidine-2,5-diyl or 1,4-phenylene, which is unsubstituted or substituted with at least one of halogen, cyano and/or methyl; R1 and R2 each independently represent alkyl with 1 to 18 carbon atoms in which optionally 1 -CH2- group or 2 non-adjacent -CH2- groups is/are replaced by -O-, -COO- and/or -OOC- and/or one -CH2-CH2- group can be replaced by -CH=CH-; with the proviso that at least one of the groups R1 and R2 must be chiral, liquid crystalline mixtures which contain these compounds and their use for optical and electro-optical purposes. |