Halogen substitution in aromatic compounds

Abstract

It is a feature of the chemistry of aromatic compounds that halogens substitute in the ring much more easily than they add. In fact substituent groups have similar effects in aromatic substitution as they have in addition to unsaturated compounds. We find that we can postulate similar mechanisms for both types. Let us them examine the principles which govern these mechanisms:- (1) Condition of the Halogen. Firstly it appears positively established that halogenation represents an electrophilic mode of attack. There is much experimental evidence in support of this, including:- (a) Bromine substitution is accelerated by electron repelling groups in the molecule and retarded by electron attracting groups.