Simple Alkyne Chains

Nomenclature of Simple Alkyne Chain Molecules

Ethyne molecule
Science Photo Library / Getty Images

An alkyne is a molecule made up entirely of carbon and hydrogen where on or more carbon atoms are connected by triple bonds. The general formula for an alkyne is CnH2n-2 where n is the number of carbon atoms in the molecule.

Alkanes are named by adding the -yne suffix to the prefix associated with the number of carbon atoms present in the molecule. A number and dash before the name denotes the number of the carbon atom in the chain that begins the triple bond.
For example: 1-hexyne is a six carbon chain where the triple bond is between the first and second carbon atoms.

Click image to enlarge the molecule.

Ethyne

This is the chemical structure of ethyne.
This is the chemical structure of ethyne. Todd Helmenstine

Number of Carbons: 2
Prefix: eth- Number of Hydrogens: 2(2)-2 = 4-2 = 2
Molecular Formula: C2H2

Propyne

This is the chemical structure of propyne.
This is the chemical structure of propyne. Todd Helmenstine

Number of Carbons: 3
Prefix: prop- Number of Hydrogens: 2(3)-2 = 6-2 = 4
Molecular Formula: C3H4

Butyne

This is the chemical structure of 1-butyne.
This is the chemical structure of 1-butyne. Todd Helmenstine

Number of Carbons: 4
Prefix: but- Number of Hydrogens: 2(4)-2 = 8-2 = 6
Molecular Formula: C4H6

Pentyne

This is the chemical structure of 1-pentyne.
This is the chemical structure of 1-pentyne. Todd Helmenstine

Number of Carbons: 5
Prefix: pent- Number of Hydrogens: 2(5)-2 = 10-2 = 8
Molecular Formula: C5H8

Hexyne

This is the chemical structure of 1-hexyne.
This is the chemical structure of 1-hexyne. Todd Helmenstine

Number of Carbons: 6
Prefix: hex- Number of Hydrogens: 2(6)-2 = 12-2 = 10
Molecular Formula: C6H10

Heptyne

This is the chemical structure of 1-heptyne.
This is the chemical structure of 1-heptyne. Todd Helmenstine

Number of Carbons: 7
Prefix: hept- Number of Hydrogens: 2(7)-2 = 14-2 = 12
Molecular Formula: C7H12

Octyne

This is the chemical structure of 1-octyne.
This is the chemical structure of 1-octyne. Todd Helmenstine

Number of Carbons: 8
Prefix: oct- Number of Hydrogens: 2(8)-2 = 16-2 = 14
Molecular Formula: C8H14

Nonyne

This is the chemical structure of 1-nonyne.
This is the chemical structure of 1-nonyne. Todd Helmenstine

Number of Carbons: 9
Prefix: non- Number of Hydrogens: 2(9)-2 = 18-2 = 16
Molecular Formula: C9H16

Decyne

This is the chemical structure of 1-decyne.
This is the chemical structure of 1-decyne. Todd Helmenstine

Number of Carbons: 10
Prefix: dec- Number of Hydrogens: 2(10)-2 = 20-2 = 18
Molecular Formula: C10H18

Isomer Numbering Scheme

This is the chemical structures of the three isomers of the hexyne alkyne molecule.
This is the chemical structures of the three isomers of the hexyne alkyne molecule: 1-hexyne, 2-hexyne and 3-hexyne. The carbon atoms are numbered from left to right in red. The number corresponds to the first carbon of the triple bond of the alkyne. Todd Helmenstine

These three structures illustrate the numbering scheme for isomers of alkyne chains. The carbon atoms are numbered from left to right. The number represents the location of the first carbon atom that is part of the triple bond.
In this example: 1-hexyne has the triple bond between carbon 1 and carbon 2, 2-hexyne between carbon 2 and 3, and 3-hexyne between carbon 3 and carbon 4.
4-hexyne is identical to 2-hexyne and 5-hexyne is identical to 1-hexyne. In these cases, the carbon atoms would be numbered from right to left so the lowest number would be used to represent the molecule's name.

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Helmenstine, Todd. "Simple Alkyne Chains." ThoughtCo, Feb. 28, 2017, thoughtco.com/simple-alkyne-chains-608217. Helmenstine, Todd. (2017, February 28). Simple Alkyne Chains. Retrieved from https://www.thoughtco.com/simple-alkyne-chains-608217 Helmenstine, Todd. "Simple Alkyne Chains." ThoughtCo. https://www.thoughtco.com/simple-alkyne-chains-608217 (accessed November 19, 2017).