Unit Overview
Carbonyl compounds and carboxylic acids
CIE A-Level Chemistry· 5 min read 📊 n/a
1. Unit at a Glance
This unit follows a logical learning sequence: we first cover carbonyl compounds (aldehydes and ketones, which share the reactive C=O double bond core) before moving to the structurally related but chemically distinct carboxylic acid functional group.
A core unifying theme is understanding how changes to the groups bonded to the carbonyl carbon modify reactivity: aldehydes are more reactive than ketones towards nucleophiles, while the hydroxyl group in carboxylic acids completely changes the reaction profile.
This unit contains two core sub-topics:
Aldehydes and ketones
Covers nomenclature, structure, oxidation, reduction, nucleophilic addition and chemical identification tests for aldehydes and ketones.
★★★⏱ 20 min
Carboxylic acids
Explores acidity, structure, preparation, and key reactions of carboxylic acids and simple carboxylate salts.
★★★⏱ 18 min
2. Common Pitfalls
Wrong move:
Confusing the results of Fehling's and Tollens' tests for aldehydes vs ketones
Why:
Only aldehydes are easily oxidised under mild test conditions, leading to different outcomes
Correct move:
Remember: both tests give positive results (silver mirror for Tollens', red precipitate for Fehling's) only for aldehydes; ketones give no visible change
Wrong move:
Assume carboxylic acids react via nucleophilic addition to C=O like aldehydes/ketones
Why:
The adjacent hydroxyl group changes reactivity through resonance stabilisation of the carboxyl group
Correct move:
Most carboxylic acid reactions involve O-H bond cleavage (acid-base reactions) or substitution of the hydroxyl group, not addition across the C=O double bond
3. Quick Reference Cheatsheet
Concept / Test | Key Rule / Formula |
|---|---|
Oxidation of aldehydes | |
Nucleophilic addition to carbonyls | Mechanism: nucleophile attacks the partially positive carbonyl carbon |
Tollens' test outcome | Aldehyde: silver mirror; Ketone: no change |
Fehling's test outcome | Aldehyde: brick-red precipitate; Ketone: no change |
Carboxylic acid acidity | , more acidic than alcohols/phenols due to resonance-stabilised carboxylate ion |
What's Next
Begin this unit by learning about aldehydes and ketones, the first core sub-topic. After completing both sub-topics in this unit, you will progress to study acyl derivatives, the next class of oxygen-containing organic compounds in the CIE 9701 syllabus.