Alkyne
Unsaturated hydrocarbons with at least one carbon–carbon triple bond.
Alkynes are unsaturated hydrocarbons containing at least one carbon–carbon triple bond. The simplest acyclic alkynes with only one triple bond form a homologous series with the general formula CnH2n−2. Traditionally known as acetylenes, the name acetylene also refers specifically to C2H2 (ethyne). Like other hydrocarbons, alkynes are generally hydrophobic.
- field
- Organic chemistry
- known_for
- Containing at least one carbon–carbon triple bond; rod-like structure; terminal alkynes are mildly acidic (pKa ~25); used as fuels and precursors to other compounds
Lore & Background
In terms of valence bond theory, the carbon atoms in an alkyne bond are sp hybridized, with two unhybridized p orbitals and two sp hybrid orbitals. Overlap of an sp orbital from each atom forms one sp–sp sigma bond, and each p orbital on one atom overlaps one on the other atom, forming two pi bonds.
Reader's Guide
Alkynes are significant in organic chemistry due to their unique triple bond structure and reactivity. Terminal alkynes, with a hydrogen atom on one end, are mildly acidic (pKa ~25) and can be deprotonated to form acetylides, which are useful in alkylation and arylation reactions. The Sonogashira reaction, using a palladium and copper catalyst, allows terminal alkynes to react with aryl halides to form arylacetylenes. Commercially, acetylene is the dominant alkyne, produced by partial oxidation of natural gas and used as a fuel and precursor to compounds like acrylates. The energy-intensive calcium carbide process, historically important for countries like Germany and China, has declined relative to hydrocarbon cracking. Alkynes also exhibit structural isomerism, with the triple bond able to occupy different positions in chains of four or more carbons.
Did You Know?
- Terminal alkynes have pKa values around 25, making them far more acidic than alkenes (pKa ~40) and alkanes (pKa ~50).
- The suffix '-yne' is used in IUPAC nomenclature to denote the presence of a triple bond, and '-diyne' is used for two triple bonds.
Frequently Asked Questions
Who is Alkyne?
Alkyne is an unsaturated hydrocarbon defined by the presence of at least one carbon–carbon triple bond. The simplest acyclic members with a single triple bond follow the general formula CnH2n−2 and are traditionally grouped under the name acetylenes.
What are Alkyne's powers or signature traits?
The triple bond gives Alkyne a rigid, rod-like geometry that locks neighboring atoms into a linear arrangement. Terminal alkynes also carry a mild acidity around pKa 25, a trait most other hydrocarbons simply lack.
How does Alkyne's story end in the real world?
In practice, Alkyne most often serves as a fuel or as a reactive precursor for building more complex organic molecules. Its versatile triple bond makes it a go-to starting material in synthetic chemistry.
Why is Alkyne important in the Chemistry Fundamentals lineup?
Alkyne fills a unique reactivity niche that alkanes and alkenes cannot cover, thanks to the electron-rich triple bond. It acts as a critical bridge between simple hydrocarbons and more elaborately functionalized compounds.
What is Alkyne's real name, and how does it differ from acetylene?
The entire family is called alkynes, while the specific two-carbon member C2H2 is known as acetylene (or ethyne in IUPAC nomenclature). So acetylene is one individual character within the broader Alkyne cast rather than the whole group.
More in Chemistry Fundamentals 1-24
Elsewhere in the Chemistry Fundamentals universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record