Aryl halides are extremely less reactive towards nucleophilic substitution. Predict and explain the order of reactivity of the following compounds towards nucleophilic substitution:

Explanation

Presence of electron-withdrawing groups at o- and p-positions w.r.t. halogen increases the reactivity of halogens towards nucleophilic substitution reactions due to the stability of the intermediate carbanion. Obviously more the number of such groups at o- and p-positions, w.r.t. halogen, higher is the reactivity. thus, the reactivity of the given aryl halides decreases in the order: IIIgtIIgtI.