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Alkenes

Explore the properties, nomenclature, and addition reactions of alkenes including ethylene, cis-trans isomers, E/Z system, stability factors, regiochemistry, and free-radical mechanisms.

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Alkenes

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Presentation Transcript

  1. Alkenes Properties Nomenclature Addition Reactions

  2. Ethylene

  3. Electron Rich p-Bond

  4. Cis and Transno rotation about p-bond

  5. Elements or Degrees of Unsaturation: p-Bond or Ring

  6. Halogens replace Hydrogens

  7. Saturated compounds with Oxygen and Nitrogen

  8. Determine the # elements of Unsaturation

  9. Alkene Nomenclature

  10. Cyclic alkenes

  11. Alkyl Groups with p-Bonds

  12. Alkylidene GroupsDouble Bonds Fused to Rings

  13. Polyenes

  14. Name these Alkenes

  15. cis-trans Isomers

  16. E/Z System

  17. What’s My Name?

  18. (Z)-4-ethyl-5-isopropyl-4-nonene

  19. Establish Priority of Substituents on Each sp2 Carbon

  20. Priorities with Multiple Bonds

  21. E or Z?

  22. E or Z?

  23. Name These

  24. Preparation of Alkenes • E2 - Elimination reactions of alkyl halides and tosylates (or mesylates) • E1 - Acid catalyzed dehydration of alcohols

  25. Hydrogenation Data Helps to Determine StabilityDHhydrogenation of Alkenes

  26. Enthalpy Change Shows Relative Energy of Alkene

  27. Both cis and trans 2-Butene are Hydrogenated to Butane

  28. “E” is More Stable than “Z” by 2.3 KJ/mol

  29. Relative Stabilities of Alkenes

  30. Hyperconjugationp bond associates with adjacent C-H s bond

  31. The Addition Reaction

  32. HBr Addition

  33. Markovnikov’s RuleThe addition of H-X across a double bond results in the more highly substituted alkyl halide as the major product.

  34. Addition of HBr or HClMarkovnikov Addition

  35. Regiochemistry Determined by Stability of Intermediate

  36. 3o Carbocation forms Preferentially

  37. Carbocation Stabilitymore highly substituted, lower energy

  38. Asymmetric Center is Generated Racemic Mixture Formed

  39. Definitions • Regioisomers – two constitutional isomers that could result from an addition reaction. • Regiospecific – only one regiosisomer forms at the expense of the other. • Regioselective – both regioisomers are formed, but one is formed in preference.

  40. Determine the major product:

  41. Rearrangements

  42. HBr Addition with RO-ORAnti-Markovnikov

  43. Free-Radical Mechanism

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