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.
Prefix: eth- Number of Hydrogens: 2(2)-2 = 4-2 = 2
Molecular Formula: C2H2
Prefix: prop- Number of Hydrogens: 2(3)-2 = 6-2 = 4
Molecular Formula: C3H4
Prefix: but- Number of Hydrogens: 2(4)-2 = 8-2 = 6
Molecular Formula: C4H6
Prefix: pent- Number of Hydrogens: 2(5)-2 = 10-2 = 8
Molecular Formula: C5H8
Prefix: hex- Number of Hydrogens: 2(6)-2 = 12-2 = 10
Molecular Formula: C6H10
Prefix: hept- Number of Hydrogens: 2(7)-2 = 14-2 = 12
Molecular Formula: C7H12
Prefix: oct- Number of Hydrogens: 2(8)-2 = 16-2 = 14
Molecular Formula: C8H14
Prefix: non- Number of Hydrogens: 2(9)-2 = 18-2 = 16
Molecular Formula: C9H16
Prefix: dec- Number of Hydrogens: 2(10)-2 = 20-2 = 18
Molecular Formula: C10H18
Isomer Numbering Scheme
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.