Tang 05 substitution & elimination reactions 2

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Tang 05 substitution & elimination reactions 2

  1. 1. SUBSTITUTION &ELIMINATION REACTIONS
  2. 2. SUBSTITUTION REACTIONS Substitution ReactionsReactions where an atom or side-chain is replaced by a different atom or side-chain. H3C-X + H2O  CH3OH + HX X + X2  + HX
  3. 3. SUBSTITUTION REACTIONS Substitution ReactionsIdentify the substitution reaction(s):a) Heat + Br2  Br + HBr UV Substitutionb) FeBr3 + Br2  Br + HBr Br Substitution Roomc) temperature + Br2  Br Halogenation
  4. 4. SUBSTITUTION REACTIONS Substitution ReactionsNitric acid may react with benzene to substitute an H with a –NO2 (nitro) group. H2SO4 + HNO3  NO2 + H2O
  5. 5. SUBSTITUTION REACTIONS Substitution ReactionsAlkyl groups may also be added to benzene groups. AlCl3 + CH3CH2Cl  CH2CH3 + HCl
  6. 6. SUBSTITUTION REACTIONS Example #1Predict the product formed when benzene reacts with chloromethane in the presence of AlCl3 catalyst. AlCl3 + CH3Cl  CH3 + HCl
  7. 7. SUBSTITUTION REACTIONS Substitution ReactionsAt first, only a single H group will be substituted in any reaction involving a cyclic or aromatic hydrocarbon.Additional substitutions on an aromatic ring will have preferences for location.
  8. 8. SUBSTITUTION REACTIONSSecond Aromatic SubstitutionWhen another group is added to an aromatic ring, rules determine the preferred location of the second group. Br + Br2  Br Br Br Br Br Br ortho meta para
  9. 9. SUBSTITUTION REACTIONS
  10. 10. SUBSTITUTION REACTIONS
  11. 11. SUBSTITUTION REACTIONS Position depends on the substituent involvedY in % Ortho- % Meta- % Para- ReactionC6H5–Y Product Product Product–O–CH3 Nitration 30–40 0–2 60–70–O–CH3 F-C Acylation 5–10 0–5 90–95–NO2 Nitration 5–8 90–95 0–5–CH3 Nitration 55–65 1–5 35–45–CH3 Sulfonation 30–35 5–10 60–65–CH3 F-C Acylation 10–15 2–8 85–90–Br Nitration 35–45 0–4 55–65–Br Chlorination 40–45 5–10 50–60
  12. 12. SUBSTITUTION REACTIONSIn the case of NH2 as a substituent, ortho and para are favouredbecause of the stability of the reaction intermediate: 4 resonance structures 3 resonance structures 4 resonance structures
  13. 13. SUBSTITUTION REACTIONSPosition depends on the substituent involved The rate of substitution determines which product is favoured
  14. 14. SUBSTITUTION REACTIONSAmines are prepared by reacting alkyl halides with NH3. CH3CH2-I + NH3  CH3CH2-NH2 + HI2° and 3° amines are produced with the addition of more alkyl halide reactants.Homework:p30 #4, 6p31 #1- 3a-c
  15. 15. ELIMINATION REACTIONS
  16. 16. ELIMINATION REACTIONSTwo adjacent atoms or side groups are removed resulting in a double bond. Conc. H2SO4 CH3CHOHCH3  CH3CH=CH2 + H2OThe reverse reaction is an addition reaction.Homework:p44 #7,8

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