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Substitution reactions of benzene

Substitution reactions of benzene. L.O.: Outline the mechanism for mononitration and monohalogenation of benzene. Homework. Q: 1&3 Extension: Q2. Recap questions. What are the three sources of evidence which led to the delocalised electron model of benzene?

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Substitution reactions of benzene

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  1. Substitution reactions of benzene L.O.: Outline the mechanism for mononitration and monohalogenation of benzene.

  2. Homework Q: 1&3 Extension: Q2

  3. Recap questions • What are the three sources of evidence which led to the delocalised electron model of benzene? • Why is benzene less reactive than alkenes?

  4. Starter activity • What is the name for the reaction between bromine and ethene? • Draw the mechanism for it • Define the term “nucleophile”

  5. Reactions involving benzene • Benzene is more stable than alkenes, therefore less reactive • Won’t react with halogens at RTP without a catalyst • Will usually undergo electrophilic substitution reactions

  6. STRUCTURE OF BENZENE

  7. STRUCTURE OF BENZENE

  8. STRUCTURE OF BENZENE

  9. NITRATION nitrobenzene Conditions conc HNO3 conc H2SO4 catalyst 50ºC

  10. Electrophile curly arrow

  11. NITRATION – ELECTROPHILIC SUBSTITUTION HNO3 + H2SO4 + H2O + HSO4- + NO2 + NO2 NO2 Formation of electrophile nitronium ion Reaction of electrophile with aromatic compound NO2 + -H H + H+ + HSO4- → H2SO4

  12. NITRATION Equation (name product) Conditions Mechanism

  13. NITRATION 2-methylnitrobenzene Conditions conc HNO3 conc H2SO4 catalyst 50ºC

  14. NITRATION Uses of nitro compounds: 1) as explosives 2) to make aromatic amines (used to make dyes) 1,3,5-trinitrotoluene TNT

  15. Name the mechanism for this reaction. Electrophilic substitution

  16. Reactions with halogens • React in the presence of a catalyst called a halogen carrier Benzene + Chlorine  Chlorobenzene + Hydrochloric acid Common halogen carriers are FeCl3, AlCl3 and AlBr3

  17. Reactions with halogens –mechanism of reaction • Electrophilic substitution Br2 + FeBr3 → Br+ + FeBr4- • The halogen carrier reacts with the halogen molecule to produce the halide ion which then goes on to react with the benzene

  18. OCR past paper Q

  19. Reactivity of cyclohexenevs benzene (4 marks)

  20. Comparing benzene with alkenes • benzene is more stable (1) • benzene π electrons are delocalised (1) • benzene has lower electron density (1) • so bromine is less polarised /attracted to it /benzene is less susceptible to electrophiles (1)

  21. Finishing off • Draw the complete mechanism for the nitration of benzene. Include the reaction conditions and catalyst • Draw the complete reaction for the chlorination of benzene

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