Alkynes are hydrocarbons containing one or more triple bonds.
The name of an alkyne contains three parts: prefix(es) stem suffix
The prefix and the stem may be preceded by a number that is known as the locator.
The name of an alkyne contains three parts: prefix(es) stem suffix
The prefix and the stem may be preceded by a number that is known as the locator.
meth - 1 carbon
eth - 2 carbons
prop - 3 carbons
but - 4 carbons
pent - 5 carbons
hex - 6 carbons
4-methylpent-2-yne
eth - 2 carbons
prop - 3 carbons
but - 4 carbons
pent - 5 carbons
hex - 6 carbons
4-methylpent-2-yne
- The ending is -yne (if no other functional groups are present)
- The stem depends on the number of carbons in the longest chain containing the triple bond.
In the alkyne shown, the longest chain containing the triple bond has five carbon atoms.
- Prefixes are used to indicate the type and position of any substituents on the longest chain.
Any atom or group of atoms replacing H at a carbon is called a substituent. Three common substituents are given below
methyl CH3–
ethyl CH3CH2–
chloro Cl–Note that saturated hydrocarbon substituents have the same name as the parent alkane except with ane substituted by -yl
- Locators are used as required to identify the position in the chain of either a functional group or a substituent.
The position of the functional group takes priority in assigning numbers to the carbons in the longest chain.
For alkynes the two carbons of the triple bond are given the lowest possible numbers. This determines the number associated with any other carbons on the chain.
In the example above the chain is numbered from the right-hand end because then the carbons of the triple bond will be C-2 and C-3 (not C-3 and C-4). This means that the methyl group is at C-4.