Liquid-crystalline, 1-substituted piperidine-4-carboxylic acid esters, process for their preparation, and their use in liquid-crystalline mixturesThe novel 1-substituted piperidine-4-carboxylic acid esters of the general formula (I) ##STR1## are liquid-crystalline and exhibit, in particular, S.sub.c or S.sub.c * phases. In this formula, R.sup.1 or R.sup.2 is a radical of the general formula (II) ##STR2## in which the rings are aromatic, heteroaromatic or optionally heteratom-containing cycloaliphatic molecular components, such as 1,4-phenylene, pyrimidine-2,5-diyl or trans-1,4-cyclohexylene, which are linked via a single bond (in the case where n and p=zero) or via functional groups Z.sub.1 or Z.sub.2 such as CO- or CH.sub.2 -O, and in which k, n, m, p and q are zero or 1, where k+m+p is at least 1 and p=zero when m=zero. The other radical R.sup.1 or R.sup.2 is an optionally substituted straight-chain or branched alkyl group having 1 to 20 carbon atoms, X.sub.1 denotes, S, phenylenoxy or CH.sub.2, and X.sub.2 denotes O or phenylenoxy.