Review of General Chemistry
Alkynes
The alkyne triple bond is composed of one σ and two π covalent bonds. The π bonds are the structures that preclude any rotation around the σ-bond axis. As with the alkenes, any rotation on the σ-bond axis would require disruption of the π-bond system. Breaking the π-bond system requires energy and thus would lead to a molecule with a less stable, higher energy state.
Like alkenes, alkynes are unsaturated because they are capable of reacting with hydrogen in the presence of a catalyst to form a corresponding fully saturated alkane. Each π bond signals that two hydrogen atoms have been lost from the molecular formula of the alkane with the same number of carbon atoms. Because alkynes possess two π bonds per molecule, they are said to contain two elements of unsaturation.
