Name alcohols, aldehydes, ketones and carboxylic acids
Apply the characteristic suffixes and position rules for common oxygen-containing organic classes.
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
Which suffix identifies an aldehyde?
What you will learn
- Name alcohols with an -OH locant
- Distinguish aldehyde and ketone suffixes
- Name a carboxylic acid with its terminal group
Use the suffix that identifies the principal group
Alcohols use -ol and a locant if the hydroxyl group can occupy different positions, for example propan-1-ol and propan-2-ol.
Aldehydes use -al for terminal –CHO, as in propanal. Ketones use -one with a carbonyl locant where needed, as in butan-2-one. The aldehyde carbon is part of the parent chain and is at its end.
Carboxylic acids have a terminal -oic acid group
Carboxylic acids use -oic acid, for example ethanoic acid and propanoic acid. The carboxyl carbon is included in the parent chain and is assigned carbon 1, so its position is not usually written.
When identifying the class, distinguish an alcohol –OH from the –OH that is part of a –COOH carboxyl group.
Pause and explain
How should the carbon of a carboxyl group be counted?
Worked example
Name CH₃CH(OH)CH₃, CH₃CH₂CHO and CH₃COCH₂CH₃.
Show the worked solution
- The alcohol has three carbons and –OH at carbon 2.
- The aldehyde has three carbons and terminal –CHO.
- The ketone has four carbons with C=O at carbon 2 from the nearer end.
Answer The names are propan-2-ol, propanal and butan-2-one.
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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.
Name CH₃CH₂CH₂OH.
Give me a hint
Count the parent and give the position of –OH.
Compare my reasoning
- There are three carbons.
- The –OH is on an end carbon, carbon 1.
- Use the alcohol suffix -ol.
Propan-1-ol.
Look for these in your work
- Parent count
- Hydroxyl locant
- Suffix
Name CH₃CH₂COCH₃.
Give me a hint
The carbonyl is inside the chain, so identify the ketone.
Compare my reasoning
- The parent has four carbons.
- Number from the end nearest C=O.
- The carbonyl is at carbon 2: butan-2-one.
Butan-2-one.
Look for these in your work
- Ketone class
- Four-carbon parent
- Lowest carbonyl locant
A learner names CH₃CH₂COOH as propan-1-ol. Correct the name.
Give me a hint
Identify the complete functional group, including the carbonyl carbon.
Compare my reasoning
- The structure ends in –COOH, not an alcohol –OH group.
- Count the carboxyl carbon: there are three carbons total.
- Use the carboxylic acid suffix.
Propanoic acid.
Look for these in your work
- Carboxyl group identified
- Carbon count correct
- Acid suffix used
Common mistakes
- Calling an aldehyde a ketone because both have C=O
- Giving a needless position for the carboxyl carbon
- Omitting the alcohol locant when positional isomers exist
What can you explain now?
Which suffix identifies an aldehyde?
Compare with the explanation
-al
A terminal –CHO group is named with -al.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do you distinguish –OH in an alcohol from –OH within a carboxylic acid?
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.