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The Mechanism

  • Date Submitted: 02/08/2012 09:41 PM
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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





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


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...


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