The correct answer is Option (2) → Acetophenone
Reactivity towards nucleophilic addition depends on:
- Nature of carbonyl compound:
Aldehydes > Ketones (ketones are less reactive due to +I effect and steric hindrance)
- Substituents on aromatic ring:
Electron-withdrawing groups increase reactivity, electron-donating groups decrease it.
Now examine each option:
- Benzaldehyde → Aldehyde, reasonably reactive
- p-Methylbenzaldehyde → Aldehyde with electron-donating group → less reactive than benzaldehyde
- p-Nitrobenzaldehyde → Aldehyde with strong electron-withdrawing group → most reactive
- Acetophenone → Ketone, more steric hindrance and +I effect of CH₃ → least reactive
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