Nitrogen-containing heterocyclic compounds of the formula IR.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 [Z.sup.2 --A.sup.3 ].sub.n --R.sup.2whereinR.sup.1 and R.sup.2 in each case independently of one another are an alkyl group with 1-15 C atoms, it also being possible for one or two non-adjacent CH.sub.2 groups to be replaced by 0 atoms and/or --CO-- groups and/or --O--CO-- groups and/or --CO--O-- groups, and one of the radicals R.sup.1 and R.sup.2 is also H, F, Cl, Br or CN,is a 1,4-cyclohexylene group, it also being possible for one or two non-adjacent CH.sub.2 groups to be replaced by 0 atoms, a 1,4-bicyclo(2,2,2)-octylene group or a 1,3-dithiane-2,5-diyl group,Z.sup.1 and Z.sup.2 in each case independently of one another are --CO--O--, --O--CO--, --CH.sub.2 CH.sub.2 --, --OCH.sub.2 --, --CH.sub.2 O-- or a single bond,A.sup.2 and A.sup.3 in each case independently of one another are a 1,4-phenylene group, pyrimidine-2,5-diyl group, 1,4-cyclohexylene group, it also being possible for one or two non-adjacent CH.sub.2 groups to be replaced by 0 atoms, 1,3-dithiane-2,5-diyl group or a 1,4-bic)cloy2,2,2)-octylene group andis 0 or 1,with the provisos that(a) at least one of the groups A.sup.2 and A.sup.3 is a pyrimidine-2,5-diyl group,(b) at least one of the groups Z.sup.1 and Z.sup.2 is not a single bond if A.sup.2 is pyrimidine-2,5-diyl and R.sup.2 is alkyl or CN,(c) Z.sup.1 is not --CO--O-- if A.sup.3 is pyrimidine-2,5-diyl and A.sup.1 is 1,4-cyclohexylene,(d) n is not 0 if A.sup.1 is 1,4-cyclohexylene and Z.sup.1 is --CH.sub.2 CH.sub.2 --, and(e) Z.sup.1 is not --CH.sub.2 CH.sub.2 -- if R.sup.2 is CN, and(f) Z.sup.1 is --CH.sub.2 CH.sub.2 --, --OCH.sub.2 -- or --CH.sub.2 O--, if A.sup.1 is 1,4-cyclohexylene and --A.sup.2 --[Z.sup.2 --A.sup.3 ].sub.n --is ##STR1## and acid addition salts thereof, can be used as components of liquid crystal phases.