In nucleophilic addition reactions, the relative reactivity order is:
AAll carbonyl compounds have equal reactivity
BAromatic aldehydes are more reactive than aliphatic
CAcetone > propanal > formaldehyde (more alkyl substitution → more reactive)
DFormaldehyde (HCHO) > acetaldehyde (CH₃CHO) > acetone ((CH₃)₂CO) — aldehydes more reactive than ketones; less steric hindrance + better electrophilic C
Answer & Solution
Correct answer: D. Formaldehyde (HCHO) > acetaldehyde (CH₃CHO) > acetone ((CH₃)₂CO) — aldehydes more reactive than ketones; less steric hindrance + better electrophilic C
**Reactivity order: HCHO > aliphatic RCHO > ArCHO > ketones**. Two reasons: (i) **steric** — alkyl groups crowd the C, hindering nucleophile approach; (ii) **electronic** — alkyl groups donate electrons (+I), reducing the partial positive charge on the carbonyl C → less electrophilic.
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