1. When a benzene ring is a substituent, it is called a
phenyl group
A benzene ring with a methylene group is called a benzyl
group

2. With the exception of toluene, benzene rings with an alkyl
substituent are named as alkyl-substituted benzenes or
as phenyl-substituted alkanes
Aryl group (Ar) is the general term for either a phenyl
group or a substituted phenyl group

3. Aromatic compounds such as benzene undergo
electrophilic aromatic substitution reactions

4. Recall in Section 3.6…

5. Benzene is a nucleophile that reacts with an electrophile
An electrophilic substitution yields an aromatic product
which is significantly more stable than the addition
reaction

6. Reaction Coordinate Diagrams for the Two Benzene Reactions

7. There are five common electrophilic aromatic substitution
reactions
Halogenation
Nitration
Sulfonation
Friedel-Crafts acylation
Friedel-Crafts alkylation

8. General Mechanism for Electrophilic Aromatic Substitution of Benzene

9. Halogenation of Benzene

10. Lewis acid weakens the Br-Br (or Cl-Cl) bond, which
makes the halogen a better electrophile

11. Mechanism for bromination
The catalyst is regenerated

14. Nitration of Benzene

16. Sulfonation of Benzene

17. Sulfonic acid is a strong acid

18. Sulfonation is reversible