The Mechanism

Electrophilic Aromatic Substitution
Reading from Vollhardt and Schore • Sections 15-8 to 15-13, 16-1 to 16-4, 16-6, and 16-7 Lecture Supplement • Electrophilic Aromatic Substitution (Thinkbook pages 25–28) Optional Reading OCATSA Chapter 24 (email instructor for access) Suggested Text Exercises from Vollhardt and Schore • Chapter 15: 24–27, 29, 32, 44, 45, 47, 48, 66 • Chapter 16: 3–9, 11–13, 23, 24, 28–38, 52, 54, 55, 58 Concept Focus Questions 1. Provide clear and concise definitions for the following terms: (a) Activating group (d) Azo dye (g) Electrophilic aromatic substitution (b) Acylium ion (e) Deactivating group (h) Sulfonic acid (c) Arenium ion (f) Diazonium salt 2. Write a generic mechanism for the electrophilic aromatic substitution reaction. Questions 3–7 refer to the reaction of toluene (PhCH3) with Br2 and FeBr3:
CH3 Br2 FeBr3
CH3 Br

CH3

CH3

+
Br

+
Br

2-Bromotoluene (ortho-bromotoluene)

3-Bromotoluene (meta-bromotoluene)

4-Bromotoluene (para-bromotoluene)

3. Provide a mechanism for the formation of 4-bromotoluene. Include all important resonance contributors. 4. Which product is major? Briefly explain. 5. What is the purpose of the FeBr3 in the reaction? 6. What is the rate-determining step in this reaction? 7. Draw a potential energy diagram for formation of the ortho product. Label all the important parts of the diagram.

Electrophilic Aromatic Substitution

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8. Explain why the reaction gives substitution and not addition products. 9. Give at least two examples each of activating and deactivating substituents. 10. As a general rule, are electron-withdrawing substituents ortho, meta, or para directors and are they activating or deactivating? Briefly explain why. 11. As a general rule, are electron-donating substituents ortho, meta, or para directors and are they activating or deactivating? Briefly explain why. 12. Briefly explain why the halogens are ortho/para directors, but deactivating. Concept Focus...