Naming alkynes follows the same rules we discussed earlier for the IUPAC nomenclature rules for alkanes.

This is the brief summary of the steps:

Step 1. Identify the parent chain.

Step 2. Identify the substituents.

Step 3. Number the parent chain, giving the triple bond the lowest locant

Step 4. Put everything together, having the substituents in alphabetical order.

And this is an example of naming an alkane:

There are two main differences you need to consider when naming alkynes:

1) The longest chain must include the triple bond.

2) Change the suffix in the parent chain from “ane” to “yne”.

The triple bond should receive the lowest possible locant in the parent chain despite the presence of alkyl substituents. The latest IUPAC recommendation is to place the locant before the suffix “yne.” However, both options are acceptable.

Let’s see how these modification affects naming in the following alkane and alkyne:

Notice that the parent chain changes from nonane to octane because it is only possible to include the triple bond in an eight-carbon continuous chain.

And the second change is the numbering – the triple bond should receive the lowest number possible, despite the presence of alkyl substituents.

For example, in this molecule, even though starting from the left would place the methyl group in position two, the triple bond in that case would have been on position 7, which is incorrect:

How to Name an Alkyne Containing Other Functional Groups

In the example above, the molecule had one functional group – the alkyne. So, what if there are halogens or a double bond?

Well, for halogens, it is easy as they do not take any advantage over the triple and double bonds, and not even simple alkyl substituents.

For example, the parent chain below is selected to include the triple bond, and it still should get the lowest possible number despite the bromo group getting number one when numbering otherwise:

How to Name an Alkyne Containing a Double Bond

If the other functional group is a double bond, there are two possible scenarios.

 1) Numbering the parent chain gives a different number to the alkene and the alkyne.

 2) Numbering the parent chain gives the same number to the alkene and the alkyne.

 If there is a difference depending on the direction you number the parent chain, simply number it in the direction producing a name with the lower number for either the double bond or the triple bond; whichever comes first – no preference for a double or a triple bond.

For example, the alkyne suffix (yne) gets the lower number in the compound on the left and the alkene suffix (en) in the compound on the right.

The alkene suffix changes from “ene” to “en”. The “e” is dropped to avoid two adjacent vowels.

Scenario 2:

If both directions for numbering the parent chain give the same number, the alkene gets a priority, so you need to number the chain in the direction that gives the double bond the lower suffix number.

For example, both directions below give either the double or triple bond locant one. However, the parent chain is numbered such that the alkene gets a lower locant than the alkyne does, even though the other substituents get higher numbers:

Notice that the second possibility shown on the right would have put the Br and Cl substituents with a lower number (3,5 beats 4,6). However, the alkene has a priority over the triple bond, and the parent chain is numbered based on this principle.

Naming Compounds with more than one functional group can get challenging. In these cases, you need to determine the priority of the functional groups and assign a suffix and prefix based on the relative priorities.
Check the following post for more details about it:

How to Name a Compound with Multiple Functional Groups

In the following practice problem, we will go over naming Alkynes following the IUPAC nomenclature rules.

The examples cover scenarios of numbering the parent chain by giving the triple bond the lowest priority when there is a tie, as well as the Alkene Alkyne naming priority when there is a double and triple bond in the molecule.