A nematic liquid crystal mixture having positive anisotropy of the dielectric constants comprising a nematogenic material having a clearing point above 60??? C. and one or more compounds of the formula ##STR18## wherein R1 and R2 are hydrogen or straight-chain alkyl, provided that at least one of R1 and R2 is other than hydrogen and that the sum of the number of carbon atoms present in R1 and R2 i