Page 1027 - Advanced Organic Chemistry Part B - Reactions & Synthesis

11

Aromatic Substitution

Reactions

Introduction

This chapter is concerned with reactions that introduce or replace substituent groups on
aromatic rings. The synthetic methods for aromatic substitution were among the first
to be developed. The basic mechanistic concepts for electrophilic aromatic substitution
and some of the fundamental reactions are discussed in Chapter 9 of Part A. These
reactions provide methods for introduction of nitro groups, the halogens, sulfonic
acids, and alkyl and acyl groups. The regioselectivity of these reactions depends upon
the nature of the existing substituent and can be ortho, meta,or para selective.

X X
E +
E

E = NO , F, Cl, Br. I, SO H, SO Cl, R, RC = O
2
2
3
A second group of aromatic substitution reactions involves aryl diazonium ions.
As for electrophilic aromatic substitution, many of the reactions of aromatic diazonium
ions date to the nineteenth century. There have continued to be methodological devel-
opments for substitution reactions of diazonium intermediates. These reactions provide
routes to aryl halides, cyanides, and azides, phenols, and in some cases to alkenyl
derivatives.
X X

Nu –
N + N Nu

Nu = F, Cl, Br, I, CN, N , OH, CH = CHR
3
1003