Name carbon chains and simple organic substituents
Choose the longest suitable chain, number it consistently and name alkyl branches and halogenoalkanes.
Section 13 · An introduction to AS Level organic chemistry
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Use the published functional-group scope and nomenclature limits; draw formula and mechanism evidence with correct connectivity, electron movement and stereochemistry. Written practice is self-checked
Before you begin
- Use covalent structures, valency, molecular formulas, lone pairs, and single, double and triple bonds.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What root represents a five-carbon parent chain?
What you will learn
- Use carbon roots for chains up to six atoms
- Locate a branch or substituent with a locant
- Name simple alkanes, alkenes and halogenoalkanes
Choose and number the parent chain
For the simple aliphatic compounds in this syllabus, select the longest continuous carbon chain as the parent. The roots for one to six carbons are meth-, eth-, prop-, but-, pent- and hex-.
Number from the end that gives the principal functional group or substituent the lowest possible locant under the naming rules being used. Show a branch such as methyl with its position; identical branches use di-, tri- and so on.
Unsaturation and halogens appear in the name
An alkene uses the -ene ending and a number for the C=C location when needed: but-1-ene and but-2-ene. Alkanes use -ane.
Halogens are named as prefixes fluoro-, chloro-, bromo- or iodo-, with a locant when there is more than one possible position, for example 2-chloropropane.
Pause and explain
How is chlorine named when it is a substituent on an alkane?
Worked example
Name CH₃CH(CH₃)CH₂CH₃ and CH₃CHClCH₃.
Show the worked solution
- The longest chain in the first structure contains four carbons.
- It has a methyl branch at carbon 2.
- The second is propane with chlorine at carbon 2.
Answer The names are 2-methylbutane and 2-chloropropane.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name CH₃CH₂CH₂CH₃.
Give me a hint
Count the longest chain and check for branches or multiple bonds.
Compare my reasoning
- There are four carbon atoms in a continuous chain.
- All C–C bonds are single.
- Use the four-carbon alkane name.
Butane.
Look for these in your work
- Four-carbon root
- Saturation checked
- Correct suffix
Name CH₃CH₂CH(CH₃)CH₃ using the lowest branch locant.
Give me a hint
Number the chain from the nearer end to the branch.
Compare my reasoning
- The longest chain has four carbons.
- The methyl branch is on carbon 2 when numbered from the nearer end.
- Combine locant, branch and parent: 2-methylbutane.
2-methylbutane.
Look for these in your work
- Parent chain chosen
- Lowest locant used
- Branch named
Name CH₃CH₂CH=CHCH₃ and state why a locant is required.
Give me a hint
Number from the end nearer the double bond.
Compare my reasoning
- The parent contains five carbon atoms.
- The double bond begins at carbon 2 from the nearer end.
- Use pent-2-ene.
Pent-2-ene; the locant distinguishes the position of the C=C bond.
Look for these in your work
- Five-carbon parent
- Correct numbering
- Unsaturation located
Common mistakes
- Choosing a shorter parent chain when a longer continuous chain exists
- Leaving out a branch locant
- Using a suffix instead of a halogen prefix
What can you explain now?
What root represents a five-carbon parent chain?
Compare with the explanation
Pent-
The five-carbon root is pent-.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
What should you inspect before deciding the number and suffix in an organic name?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.