(i) Gabriel phthalimide reaction involves the nucleophilic attack of the phthalimide on the alkyl halide.(ii) Such a nucleophilic substitution reaction is not possible if the substrate is an aryl halide.
(iii) The reason for it can be explained on the basis of
(a) Partial double bond character of C — X bond in aryl halide. Consider the followingstructures :From the resonance structures we see that the C — X bond has a double bond character in structures II, III and IV and this makes cleavage of C — X bond difficult.
(b) Also the steric hindrance by the bulkyaryl group prevents the incoming nucleophile.