Concept:The reactivity of carboxylic acid derivatives toward nucleophilic acyl substitution depends inversely on the basicity (and directly on the leaving group ability) of the substituted group.
Formula:$$ \text{Reactivity Order: Acid Chloride} > \text{Anhydride} > \text{Ester} > \text{Amide} $$
Solution:- The chloride ion (\( \text{Cl}^- \)) in acid halides is an extremely weak base and a fantastic leaving group.
- Furthermore, chlorine's high electronegativity renders the carbonyl carbon highly electrophilic and susceptible to attack.
Why other options are incorrect:Amides are the least reactive because the \( \text{NH}_2^- \) ion is a terrible leaving group and strongly donates electrons via resonance. Esters and anhydrides fall in the middle.
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