Question

\[ \text{Arrange the following compounds in increasing order of their reactivity towards }HCN: \]
\[ CH_3COCH_3,\quad CH_3CHO,\quad (CH_3)_3C-CO-CH_3 \]

Hint:

Aldehydes are generally more reactive than ketones towards nucleophilic addition. Clemmensen reduction converts carbonyl group into \(-CH_2-\) group.

Answer 1

Step 1: Mechanism.
HCN addition to a carbonyl is nucleophilic addition. $CN^-$ attacks the electrophilic carbonyl carbon. Reactivity increases with greater electrophilicity (less electron donation) and less steric crowding.
Step 2: Analysis of each compound.
$(CH_3)_3C$-$CO$-$CH_3$: very bulky, most hindered. Least reactive.
$CH_3COCH_3$ (acetone): two methyl groups reduce electrophilicity. Intermediate.
$CH_3CHO$ (ethanal): aldehyde, one methyl, least hindered. Most reactive.
Step 3: Increasing order of reactivity.
\[ \boxed{(CH_3)_3C\text{-}CO\text{-}CH_3 < CH_3COCH_3 < CH_3CHO} \]