Choose a route to make a named alcohol
Compare the syllabus routes from alkenes, halogenoalkanes, carbonyls, acids and esters.
Section 16 · Hydroxy compounds
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. State reagents and conditions, follow the stated reaction pathway, and distinguish each alcohol class and oxidation product. Written practice is self-checked
Before you begin
- Use functional-group formulae and reaction types from Topic 13, alkene reactions from Topic 14, and halogenoalkane substitution from Topic 15.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which route forms an alcohol from a halogenoalkane?
What you will learn
- Match a starting functional group to its alcohol route
- Select reagents and conditions
- Preserve carbon count and alcohol class
Identify the starting functional group first
An alkene can form an alcohol by steam/H₃PO₄ hydration or a diol by cold dilute acidified KMnO₄. A halogenoalkane gives an alcohol with aqueous NaOH and heat.
Aldehydes and ketones reduce with NaBH₄ or LiAlH₄; carboxylic acids reduce with LiAlH₄. Ester hydrolysis with dilute acid or alkali and heat also yields an alcohol.
Check product structure and conditions
Reduction preserves the carbon skeleton: aldehydes form primary alcohols, ketones secondary, and carboxylic acids primary. Ester hydrolysis gives the alcohol from the alkoxy side.
Before choosing, compare the requested OH count and position, the starting functional group and the exact conditions. Similar products can arise through different pathways.
Pause and explain
Which reagent is specified to reduce a carboxylic acid to an alcohol?
Worked example
Select a route from propene to propan-2-ol and a route from propene to propane-1,2-diol.
Show the worked solution
- A single alcohol group is formed by hydration.
- A vicinal diol is formed by cold dilute acidified KMnO₄.
- State each reagent set distinctly.
Answer Propan-2-ol: steam/H₃PO₄. Propane-1,2-diol: cold dilute acidified KMnO₄.
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.
Give two routes from but-1-ene to an oxygen-containing product and distinguish the products.
Give me a hint
One route adds one OH group; the other forms two adjacent OH groups.
Compare my reasoning
- Hydration uses steam and H₃PO₄.
- Cold dilute acidified KMnO₄ forms a diol.
- State one alcohol and one diol product class.
Steam/H₃PO₄ gives an alcohol; cold dilute acidified KMnO₄ gives butane-1,2-diol.
Look for these in your work
- Routes distinguished
- Reagents correct
- Products distinguished
Choose a reagent to convert butanone into butan-2-ol, then a reagent to convert butanoic acid into butan-1-ol.
Give me a hint
Different starting groups require different reduction choices.
Compare my reasoning
- Butanone is a ketone; NaBH₄ or LiAlH₄ reduces it.
- Butanoic acid requires LiAlH₄.
- Both products retain four carbon atoms.
Butanone: NaBH₄ or LiAlH₄. Butanoic acid: LiAlH₄. Both yield a four-carbon alcohol.
Look for these in your work
- Ketone reagent correct
- Acid reagent correct
- Carbon count retained
A student wants an alcohol from an ester but chooses steam/H₃PO₄. Correct the route.
Give me a hint
The starting functional group determines the reaction.
Compare my reasoning
- Steam/H₃PO₄ hydrates an alkene.
- An ester is hydrolysed by dilute acid or dilute alkali and heat.
- The alcohol comes from the ester alkoxy side.
Use dilute acid or dilute alkali and heat to hydrolyse the ester; identify the alcohol from its alkoxy group.
Look for these in your work
- Incorrect substrate match identified
- Hydrolysis conditions stated
- Alcohol source located
Common mistakes
- Selecting a route by the product name alone
- Ignoring whether one or two OH groups are required
- Using carbonyl reduction for a carboxylic acid without LiAlH₄
What can you explain now?
Which route forms an alcohol from a halogenoalkane?
Compare with the explanation
Aqueous NaOH and heat
Hydroxide substitutes X with OH.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Which three questions help you choose the correct syllabus route to an alcohol?
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.