Question

Reactivity order of halobenzenes towards nucleophilic substitution

Answer 1

For Nucleophilic Aromatic substitution reactions the rate is max for Florobenzene and is least for Iodobenzene

THe reason for such reactivity is that the Rate Determining Step (RDS) of this reaction is formation of Carbanion, due to attack of Nucleophile and not the expulsion of leaving group.

Thats why for such reaction availability of Strong -M group on ortho or para postion wrt the halogen is almost a necessary comdition.

Florobenzene is said to be most reactive as the delta positive charge on C will be max in this case hence ipso attack is most favored due to increased electrostatic attraction .