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Derivatives of carboxylic acids
Concepts tested here
- Nucleophilic acyl substitution
All Questions
2010 AIPMT-PRE 1 question
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Among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group isReactivity of acid derivatives towards nucleophiles depends on how electron-deficient the carbonyl carbon is and on how good the leaving group is.
In $CH_3COCl$, chlorine withdraws electrons strongly by its −I effect and its 3p orbital overlaps poorly with the 2p of carbon, so there is little resonance donation; the carbonyl carbon is the most electrophilic.
$Cl^-$ is also the weakest base among the leaving groups ($Cl^-$, $CH_3COO^-$, $CH_3O^-$, $NH_2^-$), so it is the best leaving group.
In the anhydride, ester and amide the lone pair on O or N is donated to the carbonyl group by resonance, reducing its electrophilicity; the effect is greatest in the amide.
Order of reactivity: $CH_3COCl > CH_3COOCOCH_3 > CH_3COOCH_3 > CH_3CONH_2$
Hence $CH_3COCl$ is the most susceptible to nucleophilic attack.