Liquid-crystal alkenyltolan derivative, liquid-crystal composition, and liquid-crystal display element

A liquid crystalline alkenyltolan derivative expressed by the general formula (1)

• CtH2t−1—G—(CH2)m—A1—B1—(A2—B2)n—(A3—B3)p—A4—X (1)
• wherein A1, A2, A3, and A4 independently represent a 1,4-cyclohexylene, 1,4-phenylene in which one or two hydrogen atoms may be replaced by a fluorine atom(s), dioxane-2,5-diyl, or pyrimidine-2,5-diyl group;
• B1, B2, and B3 independently represent a covalent bond, an 1,2-ethylene, 1,2-ethenylene, 1,2-ethynylene, oxymethylene, methylenoxy or carbonyloxy provided that at least one of B1, B2, and B3 represents an 1,2-ethynylene group;
• G represents a covalent bond or an oxygen atom;
• CtH2t−1 represents an alkenyl group having t carbon atoms wherein t is an integer of 2 to 10;
• m is an integer of 0 to 2;
• n and p are independently an integer of 0 or 1;
• X represents an alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a chlorine atom, a bromine atom, or a cyano group wherein one or more methylene groups or fluoromethylene groups in the alkyl group or the fluoroalkyl group may be replaced by an oxygen atom(s) or an 1,2-ethenylene group, but adjacent two methylene groups should not be simultaneously replaced by them;
• provided that when A4 represents 1,4-phenylene group which is not substituted with a fluorine atom(s), there is no case that G represents a covalent bond and t+m=3 simultaneously;
• provided that when A1 represents 1,4-phenylene group which is not substituted with a fluorine atom(s), B1 represents 1,2-ethynylene, and G represents a covalent bond, there is no case that t+m=3;
• provided that when A1 represents a 1,4-phenylene group wherein fluorine atoms replace two hydrogens and A4 represents a 1,4-cyclohexane, B1 is not a triple covalent bond;
• and each element in the molecule may be its isotope.