Question

Write the increasing order of reactivity towards the nucleophilic addition reaction.

CH${}_3$CHO, CF${}_3$CHO, CH${}_2$ = CHCHO

• A. CH${}_3$CHO < CH${}_2$ = CHCHO < CF${}_3$CHO
• B. CH${}_2$ = CHCHO > CF${}_3$CHO > CH${}_3$CHO
• C. CH${}_2$ = CHCHO > CH${}_3$CHO > CF${}_3$CHO
• D. CH${}_2$ = CHCHO < CH${}_3$CHO < CF${}_3$CHO

Answer 1

Answer: (D)

CH${}_2$ = CHCHO < CH${}_3$CHO < CF${}_3$CHO

The increasing order towards nucleophilic substion reaction is
CH${}_2$ = CHCHO < CH${}_3$CHO < CF${}_3$CHO
As the electron density on carbonyl carbon increases, the rate of nucleophilic substitution decreases.
In CH${}_2$ = CHCHO, the carbonyl group is in resonance with a carbon-carbon double bond.
Due to this, the electron density on carbonyl carbon is maximum.
In CF${}_3$CHO, the electron-withdrawing trifluoromethyl group decreases the electron density on carbonyl carbon.
Hence, the rate of nucleophile substitution is maximum.