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Chapter 7

Chapter 7. Alkene Synthesis & Reactions. sp 2  sp 3. p 172, Table 5.3. Diss. energy of double bond (H 2 C=CH 2 ): 611 kJ/mol. Diss. energy of sigma bond (CH 3 — CH 3 ): 376 kJ/mol. Dissociation energy of pi bond: 235 kJ/mol. Therefore, pi bond is more reactive than sigma bond. allylic

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Chapter 7

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  1. Chapter 7 Alkene Synthesis & Reactions Chapter 7

  2. sp2 sp3 p 172, Table 5.3 Diss. energy of double bond (H2C=CH2): 611 kJ/mol Diss. energy of sigma bond (CH3 — CH3): 376 kJ/mol Dissociation energy of pi bond: 235 kJ/mol Therefore, pi bond is more reactive than sigma bond. Chapter 7

  3. allylic 361 kJ/mol Vinylic C—H 444 kJ/mol alkyl 401 kJ/mol General Properties No rotation about the pi bond. Relatively nonpolar. Not soluble in water, but soluble in hexane, ether, etc. p 172, Table 5.3 1. Radical reactions take place at the allylic position. 2. Allylic hydrogen is more acidic than alkyl and vinylic hydrogen. Chapter 7

  4. Alkene Synthesis Chapter 7

  5. Synthesis From halides - dehydrohalogenation (minus HX): Elimination From alcohol - dehydration (minus H2O): Chapter 7

  6. Elimination Reaction Chapter 7

  7. Answer Key Chapter 7

  8. Alkene Reactions Chapter 7

  9. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  10. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  11. Alkene + HX X: Cl, Br, or I. Carbocation intermediate - is planar, incoming group can attack from above or below the plane. Markovnikov rule - regiochemistry. Review Chapter 6. Chapter 7

  12. ? 2-Chloro-3-methylheptane Alkene + HX Electrophilic Addition. Chapter 7

  13. Answer Key Chapter 7

  14. Alkene + HX - suppliment Secondary halide - carbocation. Primary halide - free radical.   Chapter 7

  15. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  16. Alkene + X2 X: Cl or Br. F is too reactive, I does not react. Chloronium or bromonium ion intermediate. Anti stereochemistry. Chapter 7

  17. Alkene + X2 Chapter 7

  18. Answer Key trans-1,2,Dichloro-1,2-dimethylcyclohexane 1,2,Dibromopropane Chapter 7

  19. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  20. DMSO - solvent, NBS - source of Br2. Halohydrin Alkene  halohydrin. Form bromonium ion intermediate. Then attack by nucleophile. Aromatic ring is inert. Anti stereochemistry. Markovnikov rule applies. Chapter 7

  21. Halohydrin Chapter 7

  22. Answer Key 1-bromo-2-propanol trans-2-bromocyclopentanol or cyclopentene bromohydrin (E)-2-Chloro-1-methly-1-cyclopentanol Chapter 7

  23. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  24. Oxymercuration Alkene  alcohol. Intermediate is mercurinium ion (similar to bromonium ion). Anti stereochemistry. Markovnikov rule applies. Chapter 7

  25. Oxymercuration Chapter 7

  26. Answer Key Chapter 7

  27. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  28. Hydroboration Alkene  alcohol. Intermediate is organoborane. Syn stereochemistry. Non - Markovnikov rule applies. Chapter 7

  29. Hydroboration Mechanism Chapter 7

  30. Hydroboration Chapter 7

  31. Answer Key Chapter 7

  32. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  33. Hydrogenation • Reduction - formation of C—H bond. • PtO2 solid catalyst - heterogeneous reaction. • syn chemistry. • “Alkenes are much more reactive than most other functional groups toward catalytic hydrogenation.” - p251 Chapter 7

  34. Hydrogenation Chapter 7

  35. Answer Key Chapter 7

  36. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  37. Hydroxylation • Forming 1,2-dialcohol or diol (glycol). • Forming cyclic osmate intermediate therefore syn stereochemistry. Chapter 7

  38. Hydroxylation Chapter 7

  39. Answer Key Chapter 7

  40. Breaking up 1,2-diol Chapter 7

  41. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  42. Alkene + Carbene Chapter 7

  43. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  44. Simmons-Smith Reaction Chapter 7

  45. Alkene + Carbene p 248 “…stereospecific … Starting from a cis alkene … only cis disubstituted cyclopropane is produced; starting from a trans alkene, only trans-disubstituted cyclopropane is produced.” Chapter 7

  46. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

  47. Oxidation • Reducing the length of the carbon skeleton. • Alkene  aldehyde and/or ketone. • Oxidizing agents are ozone or potassium permanganate. Chapter 7

  48. Alkene + Ozone Chapter 7

  49. Answer Key Chapter 7

  50. HX ether X2 CH2Cl2 KMnO4, H3O+ X2 O3 H2O(xs) Zn/H3O+ HgAc2, H2O/THF CH2I2 NaBH4 Zn(Cu) ether BH3, THF CHCl3 H2O2, OH- KOH H2 OsO4 NaHSO4, H2O Pd or Pt M halogenation anti halohydrination oxidation M anti oxymercuration M oxidation Alkene hydroboration non-M syn Simmons-Smith syn hydrogenation syn carbenation syn syn hydroxylation Chapter 7

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