Nomenclature

To name a hydrocarbon, you must

• pick the main chain and number it;
• identify all side branches;
• name each side branch in order;
• name the main chain.

As long as you can do each step individually, putting it all together isn’t that hard. It does require practice, though.

Main chain

alkane

[ prefix]ane, where prefix represents the number of carbon atoms in the main chain (see the table below)

alkene

#-[ prefix]ene; #,#-[ prefix]diene; #,#,#-[ prefix]triene; etc.; where each # represents the location of a double bond and the part in bold indicates the number of double bonds

alkyne

like alkenes, but ending in yne instead of ene

alicyclic

like alkanes/alkenes/alkynes, but add cyclo before the prefix

aromatic

always benzene

Side branches

Side branches (alkyl groups) are named like #-[ prefix]yl, #,#-di[ prefix]yl, etc., where prefix is the number of carbon atoms in the branch, each # represents the location of the branch on the main chain, and the part in bold indicates the number of this type of branch.

Propyl and butyl groups have non-systematic names for their isomers:

If there are two side branches coming off an aromatic, a classical method can be used instead of numbers: ortho or o- means 1,2; meta or m- means 1,3; and para or p- means 1,4. For example, 1,4-diethylbenzene is the same as p-diethylbenzene.

There are special names for branches that aren’t alkyl groups:

Guidelines

• Always pick the longest main chain possible.
• If there are any double or triple bonds, the main chain must contain all of them, even if this results in a shorter main chain.
• Number the main chain to prefer small numbers, prioritizing the double or triple bonds, then the side branches, and then everything in total (2,2,4 is better than 2,4,4).
• Name side branches in alphabetical order (triethyl comes before dimethyl).
• Numbers separated by commas should be listed in ascending order.
• Put commas between numbers, and hyphens at number–word boundaries.