A-Level Chemistry: Aldehydes and Ketones Syllabus
Very short summary:
In A-level Chemistry, aldehydes and ketones are studied as part of carbonyl chemistry. Students learn how to identify them, compare their properties, distinguish them using chemical tests, and explain their reactions such as oxidation, reduction, and nucleophilic addition.
1. Recognising the Functional Groups
- Aldehydes contain the
–CHO group.
- Ketones contain a
C=O group within the carbon chain.
- Students should be able to identify these functional groups in organic molecules.
2. Physical Properties
- Aldehydes and ketones do not form intermolecular hydrogen bonds with themselves.
- They can form hydrogen bonds with water.
- This affects their boiling points and solubility.
3. Oxidation and Reduction
- Aldehydes are readily oxidised to carboxylic acids.
- Ketones are not easily oxidised under normal test conditions.
- Aldehydes can be reduced to primary alcohols.
- Ketones can be reduced to secondary alcohols.
- Students may need to write equations using
[H] as the reductant.
4. Chemical Tests
- Tollens' reagent can be used to test for aldehydes.
- Fehling's solution or Benedict's solution can distinguish aldehydes from ketones.
- Acidified dichromate(VI) ions may also be used in oxidation-related tests.
- 2,4-DNPH can test for the presence of a carbonyl group.
- The iodoform reaction may also be included by some exam boards.
5. Nucleophilic Addition
- Students study nucleophilic addition reactions of carbonyl compounds.
- Reduction using reagents such as
NaBH4 is treated as nucleophilic addition.
- Reaction with
HCN in the presence of KCN forms hydroxynitriles.
- Students should be able to draw curly-arrow mechanisms for these reactions.
- They may also need to explain why aldehydes and unsymmetrical ketones can form a mixture of enantiomers.
6. Analytical and Spectroscopic Skills
- Students may use IR spectroscopy to identify the
C=O absorption in aldehydes and ketones.
- Some specifications also expect recognition of aldehyde
C–H absorptions.
- Derivative melting-point data may be used to identify specific carbonyl compounds.
7. What Students Should Be Able to Do
- Identify whether a compound is an aldehyde or a ketone.
- Predict whether it can be oxidised.
- State the product of reduction.
- Describe and explain carbonyl test results.
- Write equations and mechanisms for nucleophilic addition reactions.
- Apply this knowledge in practical and analytical questions.