Which hydrocarbons contain carbon-carbon triple bonds?

• A. Alkanes
• B. Alkenes
• C. Alkynes
• D. Cycloalkanes

Answer: (C)

Triple bonds between carbon atoms define alkynes. In these hydrocarbons, the C–C bond is made up of one sigma and two pi bonds, which makes the bond very strong and the molecule typically linear around that bond. The carbons involved are usually sp hybridized, giving about a 180-degree angle along the bond axis. The simplest example is ethyne (acetylene), with formula C2H2. Because of the triple bond, alkynes are unsaturated and can participate in reactions that add across the two pi bonds. Alkanes have only single C–C bonds and are saturated; alkenes have at least one C=C double bond; cycloalkanes are ring-shaped and contain only single bonds. So, the presence of a carbon–carbon triple bond identifies the hydrocarbon as an alkyne.