The steps
- Find the main functional group. If there's more than one, the highest priority one (table below) becomes the suffix. The others become prefixes.
- Find the parent chain: the longest carbon chain that contains the main functional group. Its length gives the stem: meth (1), eth (2), prop (3), but (4), pent (5), hex (6), hept (7), oct (8).
- Number the chain so the main functional group gets the lowest number. Then double and triple bonds. Then the substituents.
- Name and number the substituents (methyl, ethyl, chloro, hydroxy…). Use di-, tri-, tetra- for repeats: 2,2-dimethyl.
- Put the prefixes in alphabetical order, ignoring di-, tri- and so on: 2-bromo-3-methyl, not 3-methyl-2-bromo.
- Write it out: prefixes + stem + bond ending (an/en/yn) + suffix. Commas between numbers, hyphens between numbers and letters.
Functional group priority
When a molecule has more than one group, the higher one in this list is the suffix:
| Priority | Group | As suffix | As prefix |
|---|---|---|---|
| 1 (highest) | Carboxylic acid | -oic acid | carboxy- |
| 2 | Ester | -oate | alkoxycarbonyl- |
| 3 | Acyl chloride | -oyl chloride | chlorocarbonyl- |
| 4 | Amide | -amide | carbamoyl- |
| 5 | Nitrile | -nitrile | cyano- |
| 6 | Aldehyde | -al | oxo- |
| 7 | Ketone | -one | oxo- |
| 8 | Alcohol | -ol | hydroxy- |
| 9 | Amine | -amine | amino- |
| Prefix only | Halogens, alkyl groups, ethers, nitro | chloro-, methyl-, methoxy-, nitro- |
Worked examples
Common mistakes
- Numbering from the end nearer a substituent instead of the main functional group.
- Choosing a shorter chain because it's drawn straight. Trace every path through the molecule.
- Alphabetising by "di" or "tri". 2,2-Dimethyl is alphabetised under m.
- Forgetting the locant for the suffix when it's needed: propan-2-ol, not propanol.
More detail for specific groups: naming alkenes and alkynes and naming esters, amides and acid derivatives.
Quick answers
What is the order of priority of functional groups in IUPAC naming?
From highest: carboxylic acid, ester, acyl chloride, amide, nitrile, aldehyde, ketone, alcohol, amine. Halogens and alkyl groups are always prefixes.
How do you number the carbon chain in IUPAC naming?
Number from the end that gives the main functional group the lowest number. If that ties, give double and triple bonds the lowest numbers, then the substituents.
Are prefixes in alphabetical order?
Yes. Substituent prefixes go in alphabetical order, ignoring multiplying prefixes like di- and tri-. So 3-ethyl-2-methyl, and 2,2-dimethyl is sorted under m.
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