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Arenes : compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes

Arenes : compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes Alkynylbenzenes Etc. Emphasis on the effect that one part has on the chemistry of the other half. Reactivity & orientation. Example: ethylbenzene EAS in the aromatic part

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Arenes : compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes

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  1. Arenes: compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes Alkynylbenzenes Etc. Emphasis on the effect that one part has on the chemistry of the other half. Reactivity & orientation

  2. Example: ethylbenzene EAS in the aromatic part -CH2CH3 activates and directs ortho- & para- Free radical halogenation in the side chain -C6H5 activates and directs benzyl

  3. Alkylbenzenes, nomenclature: Special names

  4. others named as “alkylbenzenes”:

  5. Use of phenyl C6H5- = “phenyl” do not confuse phenyl (C6H5-) with benzyl (C6H5CH2-)

  6. Alkenylbenzenes, nomenclature:

  7. Alkynylbenzenes, nomenclature:

  8. Alcohols, etc., nomenclature:

  9. Alkylbenzenes, syntheses: • Friedel-Crafts alkylation • Modification of a side chain: • a) addition of hydrogen to an alkene • b) reduction of an alkylhalide • i) hydrolysis of Grignard reagent • ii) active metal and acid • c) Corey-House synthesis

  10. Modification of side chain:

  11. Friedel-Crafts: Ar-H + R-X, AlCl3 Ar-R + HX Ar-H + R-OH, H+  Ar-R + H2O Ar-H + alkene, H+  Ar-R

  12. Friedel-Crafts limitations: • Polyalkylation • Possible rearrangement • R-X cannot be Ar-X • NR when the benzene ring is less reactive than bromobenzene • NR with -NH2, -NHR, -NR2 groups

  13. polyalkylation The alkyl group activates the ring making the products more reactive that the reactants leading to polyalkylation. Use of excess aromatic compound minimizes polyalkylation in the lab.

  14. The electrophile in Friedel Crafts alkylation is a carbocation: R-X + AlX3 R+ R-OH + H+  R+ | | — C = C — + H+  R+ Carbocations can rearrange! 

  15. rearrangement

  16. R-X cannot be Ar-X

  17. NR with rings less reactive than bromobenzene -CHO, -COR -SO3H -COOH, -COOR -CN -NR3+ -NO2

  18. NR with –NH2, -NHR, -NR2

  19. Friedel-Crafts limitations: • Polyalkylation • Possible rearrangement • R-X cannot be Ar-X • NR when the benzene ring is less reactive than bromobenzene • NR with -NH2, -NHR, -NR2 groups • In syntheses it is often best to do Friedel-Crafts alkylation in the first step!

  20. Alkylbenzenes, reactions: • Reduction • Oxidation • EAS • a) nitration • b) sulfonation • c) halogenation • d) Friedel-Crafts alkylation • Side chain • free radical halogenation

  21. Alkylbenezenes, reduction: CH3CH3 H2, Ni H2, Ni 300oC, 100 atm.

  22. Alkylbenezenes, oxidation: CH3CH3 KMnO4 KMnO4 heat

  23. Oxidation of alkylbenzenes. 1) Syn 2) identification C8H10:

  24. Alkylbenzenes, EAS -R is electron releasing. Activates to EAS and directs ortho/para

  25. Alkylbenzenes, free radical halogenation in side chain: benzyl free radical

  26. Alkenylbenzenes, syntheses: • Modification of side chain: • a) dehydrohalogenation of alkyl halide • b) dehydration of alcohol • c) dehalogenation of vicinal dihalide • d) reduction of alkyne • (2. Friedel-Crafts alkylation)

  27. Alkenylbenzenes, synthesis modification of side chain

  28. Alkenylbenzenes, synthesis Friedel-Crafts alkylation not normally used for alkenylbenzenes. an exception:

  29. Alkenylbenzenes, reactions: • Reduction • Oxidation • EAS • Side chain • a) add’n of H2 h) oxymercuration • b) add’n of X2 i) hydroboration • c) add’n of HX j) addition of free rad. • d) add’n of H2SO4 k) add’n of carbenes • e) add’n of H2O l) epoxidation • f) add’n of X2 & H2O m) hydroxylation • g) allylic halogenation n) ozonolysis • o) vigorous oxidation

  30. Alkenylbenzenes, reactions: reduction

  31. Alkenylbenzenes, reactionsoxidation

  32. Alkenylbenzenes, reactionsEAS?

  33. Alkenylbenzenes, reactions side chain:

  34. Benzyl carbocation

  35. 100 syn-oxidation; make a model!

  36. Alkynylbenzenes, syntheses: Dehydrohalogenation of vicinal dihalides

  37. Alkynylbenzenes, reactions: • Reduction • Oxidation • EAS • Side chain • a) reduction e) as acids • b) add’n of X2 f) with Ag+ • c) add’n of HX g) oxidation • d) add’n of H2O, H+

  38. Alkynylbenzenes, reactions: reduction anti- syn-

  39. Alkynylbenzenes, reactions: oxidation

  40. Alkynylbenzenes, reactionsEAS?

  41. Alkynylbenzenes, reactions: side chain:

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