Optically active esters of 5-ethyl- and 5-vinyl-1,3-dioxolane-4-carboxylic acid, their use as doping substances in liquid crystal mixtures and the liquid crystal mixtures containing the new esters

A method for increasing spontaneous polarization of a liquid crystal mixture, which comprises adding an optically active 1,3-dioxolane-4-carboxylic ester of the formula (V) to the mixture ##STR36## in which the symbols have the following meaning:

• R.sup.1 is ##STR37## a straight-chain or branched alkyl radical having 1 to 16 carbon atoms or a straight-chain or branched alkenyl radical having 2 to 16 carbon atoms, it being possible for these radicals themselves to contain asymmetric carbon atoms, in which one or more non-adjacent --CH.sub.2 -- groups can be replaced by ##STR38## one or more H can be replaced by F, Cl, Br or CN, R.sup.2, R.sup.2', R.sup.3 and R.sup.3' are each H or an alkyl radical having 1 to 10 carbon atoms, in which one or more H can be replaced by F, or R.sup.2 and R.sup.3 or R.sup.2' and R.sup.3' together with the C(2) atom of the dioxolane ring form a cyclopentane, cyclohexane or cycloheptane ring,
• R.sup.4, R.sup.4' are vinyl or ethyl, or, if R.sup.1 is a radical of the formula (Va), H or an alkyl radical having 1 to 10 or an alkenyl radical having 2 to 10 carbon atoms, with the proviso that at least one radical R.sup.4, R.sup.4' is vinyl or ethyl,
• j and l are zero, 1 or 2,
• k and m are zero or 1,
• n is zero, 1 or 2, with the following proviso:
• if j and/or l are zero, k is zero;
• if n is zero, m is zero;
• the sum j+l+n is at least 2 and at most 3, --A.sup.1 and --A.sup.2 are ##STR39## --A.sup.3 is ##STR40## --M.sup.1 and M.sup.2 are ##STR41## and X is O.