626 CHAPTER 16 Reactions of Substituted Benzenes
16.2 Reactions of Substituents on Benzene
In Chapter 15, you learned how to prepare benzene rings with halo, nitro, sulfonic acid,
alkyl, and acyl substituents.Benzene rings with other substituents can be prepared by first synthesizing one of these
substituted benzenes and then chemically changing the substituent. Several of these re-
actions should be familiar.Reactions of Alkyl Substituents
We have seen that a bromine will selectively substitute for a benzylic hydrogen in a
radical substitution reaction. (NBS stands for N-bromosuccinimide; Section 9.5.)Once a halogen has been placed in the benzylic position, it can be replaced by a
nucleophile by means of an or an reaction (Section 10.8). A wide variety of
substituted benzenes can be prepared this way.SN 2 SN 1CH 2 CH 2 CH 3propylbenzeneBr+ NBS + HBr∆CHCH 2 CH 31-bromo-1-phenylpropaneperoxideNO 2Br
+ Br 2 FeBr^3R
+ RClAlCl 3C
RCCl ROO+ 1. AlCl^3- H 2 O
+ HNO 3 H^2 SO^4SO 3 H
+ H 2 SO 4∆+ Br−HO−CH 2 OH+ Br−−C N
CH 2 BrBr−
NH 3CH 2 NH 3CH 2 C NHO−CH 2 NH 2
+ H 2 O + Br−+benzyl alcoholbenzyl bromide phenylacetonitrilebenzylamine