IUPAC Naming Rules
Specification Reference S3.2.5
IUPAC Naming Rules
You should be able to use IUPAC (International Union of Pure and Applied Chemistry) naming rules to name a variety of organic compounds.
Steps for Naming Organic Compounds:
- Find the longest carbon chain
- Meth- (1C), Eth- (2C), Prop- (3C), But- (4C), Pent- (5C), Hex- (6C).
- Identify the main functional group (determines the suffix see table above).
- Number the carbon chain to give the lowest possible numbers to functional groups.
- Identify and name side chains (alkyl groups) as prefixes.
- Use commas between numbers and hyphens between letters and numbers.
Applying IUPAC Rules to Name Organic Compounds
Class (a–g) | Suffix | Structure / Key Rule | Examples |
---|---|---|---|
Alkanes | -ane | Only single bonds between carbon atoms. | CH4 Methane |
Alkenes | -ene | One or more C=C double bonds. Number the double bond position. | CH3CH=CHCH3 But-2-ene |
Alkynes | -yne | One or more C≡C triple bonds. | CH≡CCH3 Prop-1-yne |
Alcohols | -ol | OH (hydroxyl) group attached to a carbon atom. Number the position of the OH group. | CH3CH(OH)CH3 Propan-2-ol |
Aldehydes | -al | CHO group at the end of a molecule. No need to number the group, it's always at position 1. | CH3CH2CH2CHO Butanal |
Ketones | -one | C=O (carbonyl) group within the carbon chain. Number to show position of C=O. | CH3CH2COCH3 Butan-2-one |
Carboxylic Acids | -oic acid | COOH group at the end of the molecule. Always at position 1; no number needed. | CH3CH2CH2COOH Butanoic acid |
Naming Branched and Substituted Compounds
- Identify the longest carbon chain as the base name.
- Name alkyl groups as prefixes (methyl-, ethyl-, propyl-).
- Use numbers to indicate the position of the substituents.
Example 2-Methylpentane (C6H14)
Longest chain = pentane, with a methyl group at carbon 2.

Naming Cyclic Compounds
Cyclic compounds are named with the prefix “cyclo-”.
Example Cyclohexane (C6H12)
Six-membered ring.

Applying IUPAC Rules to Draw Structures from Names
- Identify the longest carbon chain.
- Place functional groups in the correct positions according to numbering.
Example Propan-1-ol
Longest carbon chain = 3 (prop)

Type of functional group: -OH (anol) and Bonding position on carbon 1 (-1-ol)

Giving the final structure of

Summary Table: IUPAC Naming Rules
Rule | Details | Quick Reference |
---|---|---|
Longest Chain | Choose the longest continuous carbon chain. | Meth-, Eth-, Prop-, But-, Pent-, Hex- |
Functional Group | Determines the suffix (end of name) and carbon number priority. | -ol, -al, -one, -oic acid, -ene, -yne |
Numbering | Assign lowest possible carbon numbering to the functional group and double/triple bonds. | Use 1-, 2-, etc.; commas between numbers |
Substituents | Name and number alkyl groups as prefixes; alphabetise if multiple. | 2-Methyl-, 3-Ethyl-, di-/tri- for repeats |
Punctuation | Commas between numbers; hyphens between numbers and letters. | e.g., But-2-ene; Propan-2-ol |