Chapter 23: Aryl Halides

Nucleophilic Aromatic Mechanism

As we have already seen (chapter 12),  the most common reaction of aromatic systems is electrophilic aromatic substitution  :

However, a fundamentally different type of reaction is possible for aryl halides under certain conditions:

The fundamental requirements for this nucleophilic aromatic substitution reaction are:

• ortho- or  para- nitro group or groups, and strong nucleophile, e.g. CH₃O^-
• or a very strong nucleophile, e.g. NH₂^-

   1. formation of the new σ bond from an Ar C to nucleophile
   2. breaking of the σ bond to the leaving group

Depending on the relative timing of these two events, two mechanistic pathways emerge:

• Addition-Elimination  (add Nu, loose LG)
• Elimination-Addition  (loose LG add Nu)

© Dr. Ian Hunt, Department of Chemistry