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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o1109

Which structural changes INCREASE the reactivity of a carbonyl compound towards nucleophilic addition?

  1. Areplacing a hydrogen on the carbonyl carbon by a tert-butyl group
  2. Bplacing a dimethylamino group para to the CHO group in benzaldehyde
  3. Creplacing a methyl group on the carbonyl carbon by a group
  4. Dplacing a nitro group para to the CHO group in benzaldehyde

Answer: C, D

Electron-withdrawing groups (, ) increase the positive character of the carbonyl carbon. A bulky tert-butyl group raises steric hindrance and has a +I effect, and a para group donates electrons by resonance; both reduce reactivity.
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