Connect carbonyl reactions in a synthesis route
Move between alcohols, aldehydes, ketones and hydroxynitriles while tracking functional groups and carbon count.
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Distinguish aldehydes from ketones by structure and evidence; state reagent, condition and observation. Written practice is self-checked
Before you begin
- Use carbonyl structures, alcohol oxidation and reduction from Topics 13 and 16, nucleophiles and curly arrows, and the organic reaction patterns from Topic 15.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which alcohol class oxidises to a ketone?
What you will learn
- Plan a short carbonyl route
- Select oxidation or reduction conditions
- Track carbon addition in hydroxynitriles
Match the route to the starting group and target
Primary alcohol + acidified oxidant/distil → aldehyde; secondary alcohol + acidified oxidant/distil → ketone. NaBH₄ or LiAlH₄ reduces aldehydes and ketones back to alcohols.
HCN with KCN catalyst and heat adds CN and OH across a carbonyl to give a hydroxynitrile. This addition adds one carbon through the CN group.
Account for evidence and naming
Use 2,4-DNPH for carbonyl presence; Fehling's or Tollens' tests distinguish aldehyde oxidation behavior; alkaline iodine detects CH₃CO–R.
At each step, preserve the carbon skeleton unless the reagent adds a carbon. In hydroxynitrile naming, include the nitrile carbon and number from that end.
Pause and explain
What test detects a carbonyl before HCN addition?
Worked example
Plan a route from propan-2-ol to a hydroxynitrile and state one suitable test for the carbonyl intermediate.
Show the worked solution
- Oxidise secondary propan-2-ol by distillation to propanone.
- Confirm the ketone carbonyl with 2,4-DNPH.
- Add HCN with KCN catalyst and heat; count the new nitrile carbon.
Answer Propan-2-ol → propanone (acidified K₂Cr₂O₇/KMnO₄, distil) → 2-hydroxy-2-methylpropanenitrile (HCN, KCN catalyst, heat). 2,4-DNPH tests the propanone carbonyl.
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.
Plan the reagent sequence from butan-2-ol to butan-2-one and then its hydroxynitrile.
Give me a hint
Oxidise the secondary alcohol, then add HCN.
Compare my reasoning
- Use acidified dichromate or manganate(VII) and distil.
- The carbonyl product is butan-2-one.
- Use HCN, KCN catalyst and heat; count one extra nitrile carbon.
Butan-2-ol → butan-2-one (acidified K₂Cr₂O₇/KMnO₄, distil) → hydroxynitrile (HCN, KCN catalyst, heat); the nitrile product has five carbons.
Look for these in your work
- Oxidation condition correct
- Ketone product correct
- Carbon extension noted
A proposed two-step route reduces propanone then oxidises the resulting propan-2-ol back to propanone. What does this route show?
Give me a hint
Follow the reversible functional-group changes.
Compare my reasoning
- NaBH₄/LiAlH₄ reduces ketone to secondary alcohol.
- Acidified oxidant/distillation can oxidise secondary alcohol to ketone.
- The route returns to the starting functional group rather than making a new product.
The two steps reverse one another and regenerate propanone; choose a different target reaction if a new product is required.
Look for these in your work
- Both transformations identified
- Cycle recognised
- Route evaluated
Why must the carbon count be increased when a carbonyl becomes a hydroxynitrile?
Give me a hint
Identify the source of the nitrile carbon.
Compare my reasoning
- HCN supplies CN.
- The carbon of CN bonds to the former carbonyl carbon.
- That carbon is counted in the nitrile parent.
The carbon in HCN's CN group becomes part of the product, increasing the total carbon count by one.
Look for these in your work
- CN source named
- New bond explained
- Naming consequence stated
Common mistakes
- Using reflux to isolate an aldehyde
- Forgetting ketone HCN addition also adds one carbon
- Using the carbonyl test to claim an exact structure
What can you explain now?
Which alcohol class oxidises to a ketone?
Compare with the explanation
Secondary
A secondary alcohol carbon becomes the ketone carbonyl carbon.
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Make it stick
How do oxidation, reduction, HCN addition and qualitative tests fit into a carbonyl pathway?
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.