The compound shown is compared with an anhydride, an ester and an amide of the same acyl group. Which order of reactivity toward nucleophilic acyl substitution is correct?

A $(RCO)_{2} O > RCOCl > RCOOR X^{'} > RCONH X_{2}$
B $RCOCl > RCOOR X^{'} > (RCO)_{2} O > RCONH X_{2}$
C $RCOCl > (RCO)_{2} O > RCOOR X^{'} > RCONH X_{2}$
D $RCONH X_{2} > RCOOR X^{'} > (RCO)_{2} O > RCOCl$

Answer: C

The drawn compound is acetyl chloride. Reactivity follows the leaving-group ability and the lack of resonance donation to C=O: Cl(-) is the best leaving group, then carboxylate, alkoxide, and amide (strong N lone-pair donation, poor leaving group NH2(-)) is the least reactive.

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The compound shown is compared with an anhydride, an ester and an amide of the same acyl group. Which order of reactivity toward nucleophilic acyl substitution is correct?

Answer: C

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