Name simple aromatic compounds
Use benzene as the parent ring and locate simple substituents with systematic numbering.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 29. Follow the formula, naming and optical-isomerism limits stated in the syllabus. Benzene-ring displayed formulas are not expected; use the supplied convention for aromatic skeletal formulas. Do not extend the optical-isomerism scope to naming diastereoisomers or meso compounds. Written practice is self-checked
Before you begin
- Use covalent formula conventions, functional groups, reaction terminology, and the AS organic chemistry foundations.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In 2,4,6-tribromophenol, which group defines position 1?
What you will learn
- Name simple compounds with one benzene ring
- Number one or more simple substituents to give appropriate locants
- Interpret names that include functional-group and substituent prefixes
Use benzene as the parent framework
The syllabus requires systematic names for simple aromatic molecules containing one benzene ring and one or more simple substituents. Number the ring to give the lowest valid locants, then state substituents with their positions.
Examples include nitrobenzene, chlorobenzene, methylbenzene, 3-nitrobenzoic acid and 2,4,6-tribromophenol. For a principal group included in the parent name, use the ring numbering convention consistently and locate the other substituents.
Read names as positions plus groups
In 2,4,6-tribromophenol, the phenol carbon is assigned position 1 and bromines occupy positions 2, 4 and 6. In 3-nitrobenzoic acid, the carboxyl group defines the benzoic-acid parent and nitro is at position 3.
The syllabus scope is one benzene ring with simple substituents. It does not require a full advanced aromatic nomenclature system for fused rings or multiple complex substituent hierarchies.
Pause and explain
What does the 3- in 3-nitrobenzoic acid identify?
Worked example
Interpret the name 2,4,6-tribromophenol.
Show the worked solution
- The parent is phenol, with –OH at ring position 1.
- There are three bromine substituents.
- Their positions are 2, 4 and 6.
Answer It is a phenol ring with bromine atoms at positions 2, 4 and 6 relative to the –OH group.
Try a topic test
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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.
Describe the ring substitution in 1-bromo-4-methylbenzene.
Give me a hint
Treat benzene as the parent and read each locant.
Compare my reasoning
- Bromine is at position 1.
- Methyl is at position 4.
- The two groups are opposite on the ring.
The benzene ring has Br and CH₃ at positions 1 and 4, respectively, opposite each other.
Look for these in your work
- Both locants read
- Substituents identified
- Relative position described
A student describes 2,4,6-tribromophenol as phenol with bromines on carbons 1, 3 and 5. Correct the interpretation.
Give me a hint
Use the –OH-bearing carbon as position 1.
Compare my reasoning
- Phenol's –OH carbon is position 1.
- The name explicitly gives bromine positions 2, 4 and 6.
- Do not renumber the ring to make a different pattern.
The bromines are on positions 2, 4 and 6; position 1 carries the –OH group.
Look for these in your work
- Parent reference fixed
- Locants corrected
- Substituents placed
What structural information is shared by 3-nitrobenzoic acid and 4-nitrobenzoic acid, and what differs?
Give me a hint
Compare the parent and substituent, then compare locants.
Compare my reasoning
- Both have a benzoic-acid parent and one nitro group.
- The nitro group is at position 3 in one and position 4 in the other.
- The changed locant means the substituent occupies a different ring carbon.
Both are nitrobenzoic acids; the nitro group is at carbon 3 versus carbon 4, so they are positional isomers.
Look for these in your work
- Shared parent identified
- Locants compared
- Structural difference stated
Common mistakes
- Numbering from an arbitrary carbon rather than the principal group
- Confusing substituent count with locant count
- Placing nitro or halogen at the wrong ring position
- Using advanced fused-ring names outside the stated scope
What can you explain now?
In 2,4,6-tribromophenol, which group defines position 1?
Compare with the explanation
The –OH group of phenol
The parent phenol ring starts numbering at its hydroxy-bearing carbon.
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Make it stick
How do parent groups and locants help you read or construct a simple aromatic 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.