A LITTLE LIGHTBULB MOMENT
Aldehydes, ketones and carbonyl additions
Aldehydes are usually more reactive than ketones
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Aldehydes wear one bulky backpack; ketones wear two
The idea behind the cue
Aldehydes are typically more reactive toward nucleophilic addition than ketones because they have less steric hindrance and less electron donation from alkyl groups. Ketones are both more crowded and slightly less electrophilic.
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Short & simple
Aldehydes wear one bulky backpack; ketones wear two
Acronym
AKS — Awkward Kittens Snore.
Story
At the carbonyl nightclub, an aldehyde is guarded by one bulky friend, while a ketone has two bodyguards. Incoming nucleophiles squeeze past the aldehyde bouncer more easily.
Connect the pieces
- A (Awkward) → Aldehyde reactivity: Aldehydes are usually more reactive because they are less crowded and have less alkyl electron donation.
- K (Kittens) → Ketone crowding: Ketones are more substituted, more crowded, and slightly less electrophilic.
- S (Snore) → Steric drag: Steric hindrance slows nucleophilic addition, especially for ketones.
- Awkward · Aldehyde reactivity: Aldehydes are usually more reactive because they are less crowded and have less alkyl electron donation.
- Kittens · Ketone crowding: Ketones are more substituted, more crowded, and slightly less electrophilic.
- Snore · Steric drag: Steric hindrance slows nucleophilic addition, especially for ketones.
Know the limits
This trend is for nucleophilic addition under comparable conditions; catalysts, substituents, or solvent can alter apparent rates.
Further reading · OpenStax Organic Chemistry ↗Check your understanding
Which substrate is generally more reactive toward nucleophilic addition?
A. Aldehyde
B. Ketone
C. Alkane
D. Ether
Reveal explanation
Aldehyde
Aldehydes are less hindered and usually more electrophilic than ketones.