- The principle functional group suffix of a molecule's name reflects its highest priority functional group
- If a molecule has multiple functional groups, the highest priority group dictates the suffix and the rest are named as substituents at the front of the name
Most functional groups are higher priority than the main hydrocarbon root/suffix. The highest priority functional group in a molecule is included as a suffix after the hydrocarbon suffix. All other, lower priority functional groups are included in the name as simple branching substituents.
The table below lists the principle functional group suffix, as well as the corresponding prefix in cases where it is not the highest priority group in the molecule and is instead treated as a branching substituent. Note that the table is presented in order of decreasing priority.
Expand this section to review the structure of these functional groups
When there is only one functional group from the list above in a molecule, then the only principle functional group suffix is used in the name. For example, the molecule below only contains a carboxylic acid. Therefore, the suffix “oic acid” is used as the principle functional group suffix. There are two important things to note in the final name. First, it is not necessary to list the carboxylic acid at the 1-position because carboxylic acids always start at the 1-position of the root chain (it is impossible to draw them any other way). Second, anytime two vowels are combined in a name (as in butaneoic acid), the “e” is dropped and the molecule is simply butanoic acid.
The same nomenclature format is used for any of these higher-priority functional groups. Any of the functional groups that are lower priority (i.e. halides, ethers, and sulfide) are still treated as substituents. Number the molecule closest to the highest priority functional group.
When multiple high-priority functional groups are present in the same molecule, the one with the highest priority (highest on the list on the previous page) is assigned as the principle functional group suffix. All other functional groups are treated as branching substituents and are used with their appropriate prefix. In the first example below, the ester is higher priority than the alcohol. Thus, the principle suffix is “oate” and the alcohol prefix of “hydroxy” is used as a prefix. In the second example below, the ketone takes higher priority than the thiol, while the nitrile in the third example takes higher priority than then amine.
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