Directing Effects of Substituents in Conjugation with the Benzene Ring

DIRECTING EFFECTS OF SUBSTITUENTS IN CONJUGATION WITH THE BENZENE RING 

What is the influence of substituents whose electrons are in conjugation with those of the benzene ring We can answer this question by again comparing the resonance forms of the intermediates resulting from the various modes of electrophilic attack. 

Groups that donate electrons by resonance activate and direct ortho and para 

Benzene rings bearing the groups -NH2 and -OH are strongly activated. For example, halogenations of benzenamine (aniline) and phenol not only take place in the absence of catalysts but also are difficult to stop at single substitution. The reactions proceed very rapidly and, as in activation by alkyl groups (Section 16-2), furnish exclusively ortho- and para- 

Electrophilic Brominations of Benzenamine (Aniline) and Phenol Give Ortho and Para Substitution 

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