Alkyne

An alkyne is a hydrocarbon containing at least one carbon–carbon triple bond. Its triple-bonded carbons are typically linear, and the bond makes the molecule unsaturated.

Carbon–carbon triple bond: A covalent bond in which two carbon atoms share three pairs of electrons. This bond defines alkynes and gives its carbon atoms a linear arrangement.
Hybridization: A model that describes atomic orbitals as combinations forming directed bonding orbitals. The sp hybridization of alkyne carbons accounts for their linear geometry.
Acetylene: The simplest alkyne, with molecular formula C₂H₂. Acetylene is the simplest alkyne and a major industrial feedstock.
Alkane: A saturated hydrocarbon containing only carbon–carbon single bonds. Alkanes lack the unsaturation that makes alkynes undergo addition reactions.
Alkyne hydrogenation: The addition of hydrogen across an alkyne’s triple bond to form an alkene or alkane. Hydrogenation shows how adding atoms across the triple bond changes its saturation.
Sigma bond: A covalent bond formed by electron density concentrated along the axis between two nuclei. One sigma bond forms the framework of the carbon–carbon triple bond.
Sonogashira coupling: A palladium-catalyzed reaction that couples a terminal alkyne with an aryl or vinyl halide. It uses terminal alkynes to build carbon–carbon bonds in complex molecules.
Diene: A hydrocarbon containing two carbon–carbon double bonds. Dienes offer two double-bond reaction sites but differ from alkynes in bonding and reactivity.
Lindlar catalyst: A poisoned palladium catalyst that partially hydrogenates alkynes to cis alkenes. It stops hydrogenation at the alkene stage and controls the product’s geometry.
Pi bond: A covalent bond formed by sideways overlap of parallel orbitals, with electron density above and below the bond axis. Two pi bonds accompany the sigma bond in an alkyne’s triple bond.

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