Alkyne
An alkyne is an unsaturated hydrocarbon that contains at least one carbon–carbon triple bond (C≡C), with the simplest acyclic alkynes following the general formula CₙH₂ⁿ₋₂. The triple bond comprises one sigma and two pi bonds, making alkynes highly reactive and capable of two successive addition reactions. The simplest alkyne, acetylene (ethyne), is widely used in welding torches because its combustion with oxygen produces a flame exceeding 3,500 °C.
Key Formula
CnH(2n-2)
LaTeX: C_nH_{2n-2}
| Symbol | Meaning | Unit |
|---|---|---|
| n | number of carbon atoms (n ≥ 2) | dimensionless |
Worked Example
Problem
Determine the degree of unsaturation (DoU) for propyne (C₃H₄) and confirm it matches the triple bond.
Solution
Step 1: DoU formula = (2C + 2 + N − H − X) / 2, where C = carbons, H = hydrogens, N = nitrogens, X = halogens. Step 2: For C₃H₄: DoU = (2×3 + 2 − 4) / 2 = (6 + 2 − 4) / 2 = 4/2 = 2. Step 3: A triple bond contributes 2 degrees of unsaturation (1 sigma + 2 pi bonds). Step 4: DoU = 2 is consistent with one C≡C triple bond.
Answer
DoU = 2, confirming one triple bond in propyne (CH₃–C≡CH)
Common Alkynes and Their Properties
| Name | Formula | IUPAC Name | Boiling Point (°C) | Key Use |
|---|---|---|---|---|
| Acetylene | C₂H₂ | Ethyne | −84 | Oxy-acetylene welding |
| Methylacetylene | C₃H₄ | Propyne | −23.2 | Organic synthesis |
| 1-Butyne | C₄H₆ | 1-Butyne | 8.1 | Pharmaceutical synthesis |
| 2-Butyne | C₄H₆ | 2-Butyne | 27 | Chemical intermediate |
| 1-Pentyne | C₅H₈ | 1-Pentyne | 40.2 | Research reagent |
Interactive Tools
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Related Terms
Alkene
An alkene is an unsaturated hydrocarbon containing at least one carbon–carbon double bond (C=C), with the simplest members following the general formula CₙH₂ⁿ. The double bond consists of a sigma bond and a pi bond, making alkenes more reactive than alkanes and susceptible to addition reactions. Alkenes are industrially vital — ethylene alone is the most-produced organic chemical worldwide, used to make polyethylene plastic.
Alkane
An alkane is a saturated hydrocarbon in which all carbon atoms are connected by single covalent bonds, giving the general formula CₙH₂ⁿ₊₂. Because alkanes contain no double or triple bonds, they are chemically less reactive than other hydrocarbons and are described as "paraffins" in the petroleum industry. They are the principal components of natural gas and crude oil, making them critical energy sources.
Hydrocarbon
A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon atoms, forming the simplest class of organic molecules. Hydrocarbons are classified by their bonding: saturated (single bonds only) or unsaturated (containing double or triple bonds). They are the primary constituents of fossil fuels and serve as feedstocks for the petrochemical industry.
From the IUPAC "-yne" suffix, derived from Greek "hys" (pig — a historical reference to the pungent smell of acetylene) or more likely from "alkyl" + "-yne" coined in the 1860s. August Wilhelm von Hofmann systematized the "-yne" suffix for the triple-bond hydrocarbon series.