. . . "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" . .