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elimination reaction, addition reaction, oxydation reactions

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elimination reaction, addition reaction, oxydation reaction,

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elimination reaction, addition reaction, oxydation reactions

  1. 1. Eliminations
  2. 2. Elimination ReactionsElimination Reactions E1 Reaction E2 Reaction Weak nucleophile Strong nucleophile General Mechanism General Mechanism Most commonly used bases:
  3. 3. E1 Reaction: Stereochemistry Substitution predominates largely And Elimination is a minor process! Zaitsev’s Rule is followed here, strictly!
  4. 4. E2 Reaction: Stereochemistry Syn Elimination: Uncommon Anti Elimination: Very common Example:Example: The requirement of trans relationship
  5. 5. E2 Reaction: Direction of Elimination Zaitsev’s rule: More substituted olefin is favored! Hofmann’s rule: Least substituted olefin is favored! Reasons: Acidity and Sterics! Steric and Electronic Factors in Eliminations: More conjugated and not More substituted!
  6. 6. Summary of Eliminations
  7. 7. Elimination Reactions: Synthetic Applications Dehydrohalogenations: Dehydrations: Oxidations: Loss of H2
  8. 8. Competition Between Elimination and Substitutions SN2 versus E2N • A good base/nucleophile (avoids SN1) favors SN2/E2 • Sterically bulky base can favor E2 (pentacoordinated TS not possible)! All SN2 or E2! Tertiary, yet E2 with a strong base/nucleophile! All SN2 or E2! • Strong base/nucleophile always promotes elimination and a weaker base/nucleophile always yields substitution products prediminantly!
  9. 9. Competition Between Elimination and Substitutions SN1 versus E1N CH3L:   No -carbon, exellent substrate for SN2, no SN1 possible, elimination cannot occur! RCH2L:   Less sterics, exellent substrate for SN2, but predominantly E2 with a strong base!2 , , p y g R2CHL:   SN2 with CH3COO-, CN-, RS-, etc.) E2 with OH-, OR-, DBU, DBN, etc. In a polar solvent: SN1 and E1 in the absence of a good nucleophile or base R3CL:   No SN2, no SN1 if substittuion is needed (no base!) E cellent Elimination ith a strong base b E2!Excellent Elimination with a strong base by E2!
  10. 10. Addition Reactions
  11. 11. Addition of Oxygen to Olefins: Epoxidation Dih d l ti f Ol fiDihydroxylation of Olefins: Trans‐dihydroxylation Cis‐dihydroxylation
  12. 12. Hydrationby Oxymercuration Hydroboration by Hydroboration Terminal  Alkyne: Internal  Alkyne:
  13. 13. Conjugate Addition: 1,2 versus 1,4 Addition
  14. 14. Conjugate Additions (Michael Reaction Mi h l Additi )Michael Addition)
  15. 15. Bromination of Olefins
  16. 16. Addition of Br2 to Triple Bonds
  17. 17. Reduction of Alkynes Lindlar Catalyst: Pd/CaCO3 or BaSO4 deactivated with Lead Tetraacetate and QuinolineLindlar Catalyst: Pd/CaCO3 or BaSO4 deactivated with Lead Tetraacetate and Quinoline Trans addition of H2Trans addition of H2
  18. 18. Industrial Synthesis of Vitamin A by Hoffmann-LaRoche Pharmaceutical Company Involves reduction (Lindlar) followed by thermal isomerization!
  19. 19. Cyclopropane Synthesis Addition is  Stereospecific!
  20. 20. Simmons-Smith Reaction Carbenoid, a carbene like! Additions are stereospecific!
  21. 21. Radical Additions

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