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 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.
Alkanes are named by adding the 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
Todd Helmenstine
Number of Carbons: 2
Prefix: eth- Number of Hydrogens: 2(2)-2 = 4-2 = 2
Molecular Formula: C2H2
Prefix: eth- Number of Hydrogens: 2(2)-2 = 4-2 = 2
Molecular Formula: C2H2
Propyne
Todd Helmenstine
Number of Carbons: 3
Prefix: prop- Number of Hydrogens: 2(3)-2 = 6-2 = 4
Molecular Formula: C3H4
Prefix: prop- Number of Hydrogens: 2(3)-2 = 6-2 = 4
Molecular Formula: C3H4
Butyne
Todd Helmenstine
Number of Carbons: 4
Prefix: but- Number of Hydrogens: 2(4)-2 = 8-2 = 6
Molecular Formula: C4H6
Prefix: but- Number of Hydrogens: 2(4)-2 = 8-2 = 6
Molecular Formula: C4H6
Pentyne
Todd Helmenstine
Number of Carbons: 5
Prefix: pent- Number of Hydrogens: 2(5)-2 = 10-2 = 8
Molecular Formula: C5H8
Prefix: pent- Number of Hydrogens: 2(5)-2 = 10-2 = 8
Molecular Formula: C5H8
Hexyne
Todd Helmenstine
Number of Carbons: 6
Prefix: hex- Number of Hydrogens: 2(6)-2 = 12-2 = 10
Molecular Formula: C6H10
Prefix: hex- Number of Hydrogens: 2(6)-2 = 12-2 = 10
Molecular Formula: C6H10
Heptyne
Todd Helmenstine
Number of Carbons: 7
Prefix: hept- Number of Hydrogens: 2(7)-2 = 14-2 = 12
Molecular Formula: C7H12
Prefix: hept- Number of Hydrogens: 2(7)-2 = 14-2 = 12
Molecular Formula: C7H12
Octyne
Todd Helmenstine
Number of Carbons: 8
Prefix: oct- Number of Hydrogens: 2(8)-2 = 16-2 = 14
Molecular Formula: C8H14
Prefix: oct- Number of Hydrogens: 2(8)-2 = 16-2 = 14
Molecular Formula: C8H14
Nonyne
Todd Helmenstine
Number of Carbons: 9
Prefix: non- Number of Hydrogens: 2(9)-2 = 18-2 = 16
Molecular Formula: C9H16
Prefix: non- Number of Hydrogens: 2(9)-2 = 18-2 = 16
Molecular Formula: C9H16
Decyne
Todd Helmenstine
Number of Carbons: 10
Prefix: dec- Number of Hydrogens: 2(10)-2 = 20-2 = 18
Molecular Formula: C10H18
Prefix: dec- Number of Hydrogens: 2(10)-2 = 20-2 = 18
Molecular Formula: C10H18
Isomer Numbering Scheme
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.
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.
