Chemistry of Benzene Electrophilic Aromatic Substitution

3 Alkylation and Acylation of Aromatic Rings The Friedel-Crafts Reaction 

4 Substituent Effects in Substituted Aromatic Rings An Explanation of Substituent Effects 

Polysubstituted Benzenes A Deeper Look— Combinatorial Chemistry 

In the preceding chapter, we looked at ammatkity—the stability associated with benzene and related compounds that contain a cyclic conjugated system of 4n + 2 17 electrons. In this chapter, we ll look at some of the unique reactions that aromatic molecules undergo. 

The most common reaction of aromatic compounds is electrophilic aromatic substitution, in which an electrophile (E ) reacts with an aromatic ring and substitutes for one of the hydrogens. The reaction is characteristic of all aromatic rings, not just benzene and substituted benzenes. In fact, the ability of a compound to undergo electrophilic substitution is a good test of aromaticity. 

The most common reaction of aromatic compounds is electrophilic matic substitution. That is, an electrophile (E ) reacts with an aromati ring and substitutes for one of the hydrogens  

All these reactions—and many more as well—take place by a similar mechanism. Let s begin a study of the process by looking at one reaction in detail, the bromination of benzene. 

A benzene ring, with its six n electrons in a cyclic conjugated system, is a site of electron density. Furthermore, the benzene tt electrons are sterically accessible to attacking reagents because of their location above and below the plane of the ring. Thus, benzene acts as an electron donor (a Lewis base, or nucleophile) in most of its chemistry, and most of its reactions take place with electron acceptors (Lewis acids, or electrophiles). For example, benzene reacts with Br. in the presence of FeBrs as catalyst to yield the substitution product bromobenzene. 

CHAPTER 16 Chemistiy of Benz ne Electrophilic Aromatic Substitution 

Online homework for this chapter may be assigned in Organic OWL. 

Thomson Click Organ/c Process to view an animation of the bromination of aromatic rings. 

Thomson iO Click Organic interactive to practice your problem-solving skills on the mechanism of electrophilic aromatic substitution. 

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CHAPTER 16 Chemistry of Benzene Electrophilic Aromatic Substitution... 

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