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Chemistry · Ch 9 — Hydrocarbons

Alkynes

9.4

Alkynes

Alkynes — The Triple‑Bonded Hydrocarbons

Alkynes are unsaturated hydrocarbons that contain at least one carbon‑carbon triple bond. Because a triple bond uses three pairs of electrons, each triple bond reduces the number of hydrogen atoms by four compared to the corresponding alkane. The general formula for a straight‑chain or branched alkyne with one triple bond is

CXnHX2n−2\ce{C_nH_{2n-2}}

For n=2n=2, the formula gives CX2HX2\ce{C2H2} — ethyne, commonly called acetylene. Acetylene is the first stable member of the alkyne series and is industrially important: when burned with pure oxygen it produces an oxyacetylene flame hot enough for cutting and welding metals.

Note

The name “acetylene” is the common (trivial) name for ethyne. In the IUPAC system, the suffix -yne replaces the -ane of the corresponding alkane, and the position of the triple bond is indicated by the lowest possible number.

Alkynes serve as starting materials for a vast range of organic compounds — from polymers to pharmaceuticals — making their study essential. …

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