Build names from the carbon framework and functional group, then reverse the process to reconstruct an unambiguous structure.
Choose the parent before numbering
For the simple compounds here, select the longest appropriate chain containing the principal functional group and any relevant multiple bond. A bent chain on the page is still one continuous chain. Do not count a branch twice or jump between atoms that are not bonded.
The first six parent stems are meth-, eth-, prop-, but-, pent- and hex-. A ring uses cyclo-, for example cyclohexane. An alkyl substituent is obtained by removing H from an alkane: methyl is –CH₃ and ethyl is –CH₂CH₃. AQA nomenclature in this section is limited to chains and rings with up to six carbon atoms each; branches can make the total larger than six.
Numbering, branches and punctuation
Give the principal suffix group its lowest possible locant, then apply the relevant multiple-bond and substituent numbering rules. For simple branched alkanes compare the two sets of locants at the first point of difference: the lower number there wins. Do not use the lowest sum as a general rule.
Put substituent prefixes in alphabetical order, ignoring multiplying prefixes such as di- and tri-. Separate numbers with commas and numbers from words with hyphens. Use a locant wherever omitting it could leave the structure ambiguous.
Functional-group names
An aldehyde carbon and a carboxylic-acid carbon belong to the parent chain. In these simple terminal groups they are carbon 1. A carbonyl group in the middle of the chain gives a ketone. In an ester, name the group attached to oxygen as an alkyl group first, then name the acid-derived part as an alkanoate.
| Formula | Name | Reason |
|---|---|---|
| CH₃CH₂CH₂CH₂OH | butan-1-ol | Number from the OH end |
| CH₃CH₂CH=CHCH₃ | pent-2-ene | Use the lower carbon number of C=C |
| CH₃CH₂CH₂CHO | butanal | Include the CHO carbon |
| CH₃COCH₂CH₂CH₃ | pentan-2-one | Locate the C=O carbon |
| CH₃CH₂COOH | propanoic acid | Three carbons including COOH |
| CH₃CH₂COOCH₃ | methyl propanoate | Methyl on O; three-carbon acid part |
| HOCH₂CH₂CH₂OH | propane-1,3-diol | Keep e before diol |
| HOOCCH₂COOH | propanedioic acid | Three-carbon chain with two acid groups |
Work backwards from a name
To draw 3-methylpentan-2-ol, first write a five-carbon chain, attach OH to carbon 2 and CH₃ to carbon 3, then fill each carbon to four bonds. The condensed structure is CH₃CH(OH)CH(CH₃)CH₂CH₃. Count six carbons and fourteen hydrogens overall: C₆H₁₄O.
For 1,3-dimethylcyclopentane, make a five-carbon ring and attach methyl groups at ring positions 1 and 3. Each substituted ring carbon is CH; the other three are CH₂. Together with two CH₃ groups this gives C₇H₁₄. A flat ring sketch shows connectivity and is not a claim that the actual saturated ring is flat.
Diagram placeholder
Drawing from a name: 3-methylpentan-2-ol
Labels to include:
- parent chain C1–C5
- OH on C2
- methyl on C3
- four bonds at every carbon
- C₆H₁₄O check
Draw five linked carbons. C1 and C5 are CH₃; C2 is CH bonded to OH; C3 is CH bonded to CH₃; C4 is CH₂. Display all bonds when a displayed formula is requested. In a skeletal version retain the OH label and use a short branch line for methyl.
Quick checks
Original Finesse questions. Reveal the indicative worked solutions after attempting each question; these are not official AQA mark allocations.
Q1. Name CH₃CH₂CH(CH₃)CH₂CH₃.Show answer
3-methylpentane. The longest chain contains five carbons, with one methyl branch at carbon 3.
Q2. Name CH₃CH₂CH(OH)CH₃ and explain the numbering.Show answer
Butan-2-ol. Number from the end nearer OH, giving 2 rather than 3.
Q3. Write a condensed structural formula for 2,2-dimethylbutane and find its molecular formula.Show answer
CH₃C(CH₃)₂CH₂CH₃. The central carbon already has four C–C bonds, so carries no hydrogen. Total formula: C₆H₁₄.
Q4. Name CH₃COOCH₂CH₂CH₃.Show answer
Propyl ethanoate. The oxygen-linked alkyl group has three carbons; the acid-derived part, including the carbonyl carbon, has two.
Q5. Name HOCH₂CH₂CHO. Why is it not a propanol name?Show answer
3-hydroxypropanal. The aldehyde is the principal suffix group, so its carbon is C1; the alcohol is represented by hydroxy- at C3.
Sources
Sources and examiner guidance (reviewed 2 October 2026)
- Chemrevise: Introduction to organic chemistry — Coverage checklist, pp1–9. Explanations and practice on this site are original.
- AQA 7405 specification — 3.3.1: nomenclature, reaction mechanisms and isomerism.
- AQA June 2022 AS Paper 2 mark scheme — Q03.5 p18: formula and valid compound names.
- AQA June 2022 AS Paper 2 examiner report — Q03.5 p4: translating a formula into named compounds.
Finesse Tuition is not endorsed by AQA or Chemrevise. All explanations and examples here are our own.