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Reactivity of Carboxylic Acid Derivatives
Concepts tested here
- Leaving group ability in acyl substitution
All Questions
2008 AIPMT 1 question
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The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of -The relative reactivity of acyl compounds ($RCO-L$) towards nucleophilic substitution depends upon the leaving group ability of $L$.
Weak bases are good leaving groups.
Basic strength increases in the order: $Cl^- \lt RCOO^- \lt RO^- \lt NH_2^-$
Therefore leaving group ability decreases in the order: $Cl^- \gt RCOO^- \gt RO^- \gt NH_2^-$
Also, the lone pair on the group attached to the carbonyl carbon is donated by resonance most strongly in amides and least in acyl chlorides, so the carbonyl carbon is most electrophilic in the acyl chloride.
Hence the reactivity order is: $RCOCl \gt (RCO)_2O \gt RCOOR \gt RCONH_2$
That is, acyl chloride > acid anhydride > ester > amide.