Arrange the following aryl halides in decreasing order of reactivity towards Aromatic Nucleophilic Substitution (): (I), (II), (III), (IV).

Question

Arrange the following aryl halides in decreasing order of reactivity towards Aromatic Nucleophilic Substitution ($S_NAr$): $Ar-F$ (I), $Ar-Cl$ (II), $Ar-Br$ (III), $Ar-I$ (IV).

Prashant Kotian · Accepted Answer

Correct answer: A. The rate of the mechanism (Addition-Elimination) depends on the electron-withdrawing inductive effect () of the halogen, which stabilizes the intermediate carbanion (Meisenheimer complex) during the rate-determining attack of the nucleophile. Because Fluorine is the most electronegative, is the most reactive. The leaving group ability is not the deciding factor in the slow step. The correct order is .

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