Liquid crystalline ethane derivatives, their preparation and the liquid crystal compositions containing same

Liquid crystalline ethane derivatives by the described method in order to form liquid crystalline compositions with known liquid crystalline compounds have a general formula I: I wherein, if ring A idicates a 1,4-substituted benzene ring, then ring B indicates 1.4-substituted benzene ring or 1.4-trans-substituted cyclohexane ring or 1.4-substituted bicyclo[2,2,2]octane ring or 2.5-substituted pyrimidine ring or 2.5-substituted 1.3- dioxane ring, or if ring B indicates a 1.4-substituted benzene ring, then A indicates 1.4-trans-substituted cyclohexane ring or 1.4-substituted bicylo[2,2,2]octane ring or 2.5-substituted pyrimidine ring or 2.5-substituted 1.3-dioxane ring, and R indicates a normal alkyl chain CnH2n+1 or a non-branched alkoxy group CnH2n+1O or an alkylcarboxylic group CnH2n+1COO or an alkyl carbonato group CnH2n+1OCOO or a branched alkyl chain CH3-CH2-CH(CH3)-(CH2)k- or a branched alkoxy group CH3-CH2-CH(CH3)-(CH2)k-O, where n is an integer number and assumes values from 1 to 12, k is an integer number and assumes values from 1 to 3 and l and m assume values 1 or 0 fulfilling the condition that l+m>0, and if ring A denotes 1.4-disubstituted bicyclo[2,2,2] octane ring also l+m=0. Liquid crystalline compositions containing the compound of formula I are characterized by low viscosity and are applied in displays.