IUPAC Nomenclature
IUPAC (International Union of Pure and Applied Chemistry) created a rule system so that any organic compound has a single, unambiguous name based purely on its structure. This page summarizes the main rules — to see the name of a specific molecule instantly, build it in the simulator.
The general structure of an IUPAC name
A systematic name follows this pattern:
For example, in 2-methylbutan-2-ol: "2-methyl" is the substituent prefix, "but" indicates a 4-carbon chain, "an" indicates only single bonds, and "2-ol" is the alcohol suffix at position 2.
1. Finding the main chain
The main chain is the longest one containing the highest-priority functional group (see the full order in functional groups). In case of a tie in length, the chain with more branches is chosen.
2. Numerical prefixes (how many carbons)
| Carbons | Prefix | Carbons | Prefix |
|---|---|---|---|
| 1 | meth | 6 | hex |
| 2 | eth | 7 | hept |
| 3 | prop | 8 | oct |
| 4 | but | 9 | non |
| 5 | pent | 10 | dec |
3. Numbering the chain (locants)
Numbering starts from the end that gives the lowest locant to the main group. In case of a tie, the lowest set of locants goes to unsaturations (double/triple bonds), then to substituents, with alphabetical order breaking further ties.
4. Suffixes by function (summary)
| Function | Suffix | Example |
|---|---|---|
| Alcohol | -ol | ethanol |
| Aldehyde | -al | methanal |
| Ketone | -one | propanone |
| Carboxylic acid | -oic acid | ethanoic acid |
| Amine | -amine | methanamine |
| Nitrile | -nitrile | ethanenitrile |
See each functional group page for specific rules (esters and ethers, for example, don't follow this simple single-suffix pattern).
5. Substituent prefixes and multipliers
Branches and secondary groups (that aren't the main group) become prefixes, in alphabetical order: chloro-, methyl-, hydroxy-, etc. When the same substituent repeats, di-, tri-, tetra- are used (which don't count for alphabetical ordering).
Test these rules in the simulator →