Compound of the formula with the meanings: X is C=O, O or S, Yis HorF, R 1, R 2 are, identically or differently, hydrogen or a straight-chain or branched alkyl radical having 1 to 16 C atoms or a straight-chain or branched alkenyl radical having 2 to 16 C atoms, in which a) one or more non-adjacent and non-terminal CH 2 groups may be replaced by -O-, -C(=O)O-, -O-C(=O)-, -O-C(=O)-O-, -C(=O)- or -Si(CH 3) 2 -, and/or b) one CH 2 group may be replaced by -C≡C-, cyclopropane-1,2-diyl or cyclobutane-1,3-diyl, and/or c) one or more H atoms may be replaced by F or Cl, and/or d) the terminal CH 3 group may be replaced by one of the following chiral groups (optically active or racemic): where R 3 is a straight-chain or branched alkyl radical having 1 to 12 C atoms or a straight-chain or branched alkenyl radical having 2 to 12 C atoms, in which one or more non-adjacent and non-terminal CH 2 groups may be replaced by-O- and/or one or more H atoms may be replaced by F or Cl, with the proviso that only one of R 1, R 2 can be hydrogen, M 1, M 2 are, identically or differently, -C(=O)-O-, -O-C(=O)-, -CH 2 -O-, -O-CH 2 -, -CF 2 -O-, -O-CF 2 -, -CH=CH-, -CF=CF-, -C≡C-, -CH 2 -CH 2 -C(=O)-O-, -O-C(=O)-CH 2 -CH 2 -, -CH 2 -CH 2 -, -CF 2 -CF 2 -, -(CH 2) 4 - or a single bond, A 1, A 2 are, identically or differently, 1,4-phenylene, in which one or two H atoms may be replaced by F, Cl or CN, pyridine-2,5-diyl, in which one H atom may be replaced by F, pyrimidine-2,5-diyl, 1,4-cyclohexylene, in which one or two H atoms may be replaced by CH 3 or F, 1-cyclohexene-1,4-diyl, in which one H atom may be replaced by CH 3 or F, or 1,3-dioxane-2,5-diyl, m, n are, independently of one another, 0 or 1, but in total are not greater than 1. X is C=O, O or S, Yis HorF, R 1, R 2 are, identically or differently, hydrogen or a straight-chain or branched alkyl radical having 1 to 16 C atoms or a straight-chain or branched alkenyl radical having 2 to 16 C atoms, in which a) one or more non-adjacent and non-terminal CH 2 groups may be replaced by -O-, -C(=O)O-, -O-C(=O)-, -O-C(=O)-O-, -C(=O)- or -Si(CH 3) 2 -, and/or b) one CH 2 group may be replaced by -C≡C-, cyclopropane-1,2-diyl or cyclobutane-1,3-diyl, and/or c) one or more H atoms may be replaced by F or Cl, and/or d) the terminal CH 3 group may be replaced by one of the following chiral groups (optically active or racemic): where R 3 is a straight-chain or branched alkyl radical having 1 to 12 C atoms or a straight-chain or branched alkenyl radical having 2 to 12 C atoms, in which one or more non-adjacent and non-terminal CH 2 groups may be replaced by-O- and/or one or more H atoms may be replaced by F or Cl, with the proviso that only one of R 1, R 2 can be hydrogen, a) one or more non-adjacent and non-terminal CH 2 groups may be replaced by -O-, -C(=O)O-, -O-C(=O)-, -O-C(=O)-O-, -C(=O)- or -Si(CH 3) 2 -, and/or b) one CH 2 group may be replaced by -C≡C-, cyclopropane-1,2-diyl or cyclobutane-1,3-diyl, and/or c) one or more H atoms may be replaced by F or Cl, and/or d) the terminal CH 3 group may be replaced by one of the following chiral groups (optically active or racemic): where R 3 is a straight-chain or branched alkyl radical having 1 to 12 C atoms or a straight-chain or branched alkenyl radical having 2 to 12 C atoms, in which one or more non-adjacent and non-terminal CH 2 groups may be replaced by-O- and/or one or more H atoms may be replaced by F or Cl, M 1, M 2 are, identically or differently, -C(=O)-O-, -O-C(=O)-, -CH 2 -O-, -O-CH 2 -, -CF 2 -O-, -O-CF 2 -, -CH=CH-, -CF=CF-, -C≡C-, -CH 2 -CH 2 -C(=O)-O-, -O-C(=O)-CH 2 -CH 2 -, -CH 2 -CH 2 -, -CF 2 -CF 2 -, -(CH 2) 4 - or a single bond, A 1, A 2 are, identically or differently, 1,4-phenylene, in which one or two H atoms may be replaced by F, Cl or CN, pyridine-2,5-diyl, in which one H atom may be replaced by F, pyrimidine-2,5-diyl, 1,4-cyclohexylene, in which one or two H atoms may be replaced by CH 3 or F, 1-cyclohexene-1,4-diyl, in which one H atom may be replaced by CH 3 or F, or 1,3-dioxane-2,5-diyl, m, n are, independently of one another, 0 or 1, but in total are not greater than 1.