1. Nomenclature & Functional Groups
IUPAC nomenclature is a naming code: every legal name encodes the exact structure, and every structure has exactly one preferred name. Master the functional groups first — the suffix tells you the family.
Functional Group Reference
- Alkane: single bonds only — suffix -ane (e.g., hexane)
- Alkene: C=C double bond — suffix -ene (e.g., hex-2-ene)
- Alkyne: C≡C triple bond — suffix -yne (e.g., hex-1-yne)
- Alcohol: –OH — suffix -ol (e.g., ethanol)
- Aldehyde: –CHO — suffix -al (e.g., ethanal)
- Ketone: C=O within the chain — suffix -one (e.g., propanone)
- Carboxylic acid: –COOH — suffix -oic acid (e.g., ethanoic acid)
- Ester: –COOR — suffix -oate (e.g., methyl ethanoate)
- Amine: –NH2 — suffix -amine (e.g., ethanamine)
Naming Alkanes
1. Find the longest continuous carbon chain. 2. Number it so substituents get the lowest locants. 3. Name substituents alphabetically with their position numbers.
Example: $\text{CH}_3\text{–CH}_2\text{–CH}(\text{CH}_3)\text{–CH}_2\text{–CH}_3$ — longest chain is 5 carbons (pentane) with a methyl group on carbon 3:
3-methylpentane
3-methylpentane
Alkenes and Alkynes
Number the chain so the multiple bond gets the lowest possible locant.
Example: $\text{CH}_2\text{=CH–CH}_2\text{–CH}_3$ — the double bond starts at carbon 1:
but-1-ene (also written 1-butene)
but-1-ene (also written 1-butene)
Practice Problems
- Name: CH3–CH(CH3)–CH2–CH2–CH3
- Name: CH3–C≡C–CH2–CH3
- Draw (line structure or condensed formula): 4-ethyl-2-methylhexane.
- Which has the higher priority for numbering — a double bond or a methyl substituent?
Answers: 1. 2-methylpentane 2. pent-2-yne 3. CH3–CH(CH3)–CH2–CH(CH2CH3)–CH2–CH3 4. The double bond — unsaturation outranks substituents for the lowest locant.