ALDEHYDES AND KETONES

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ALDEHYDES AND KETONES

  1. 1. Organic Chemistry 4th EditionQBA Miguel A. Castro Ramírez Chapter 18 Carbonyl Compounds II Radicals Irene Lee Case Western Reserve University Cleveland, OH
  2. 2. Nomenclature of Aldehydes
  3. 3. If the aldehyde group is attached to a ring,
  4. 4. If a compound has two functional groups, the one with thelowest priority is indicated by its prefix
  5. 5. Nomenclature of Ketones
  6. 6. If a ketone has a second functional group of higherpriority,
  7. 7. An aldehyde has a greater partial positive charge on itscarbonyl carbon than does a ketone
  8. 8. • Steric factors contribute to the reactivity of an aldehyde• The carbonyl carbon of an aldehyde is more accessible to the nucleophile• Ketones have greater steric crowding in their transition states, so they have less stable transition states
  9. 9. Aldehydes and ketones react with nucleophiles to formaddition products: nucleophile addition reactions
  10. 10. If the nucleophile that adds to the aldehyde or ketone isan O or an N, a nucleophilic addition–elimination reactionwill occur
  11. 11. Formation of a New Carbon–Carbon Bond Using Grignard ReagentsGrignard reagents react with aldehydes, ketones, andcarboxylic acid derivatives
  12. 12. Reaction with Acetylide Ions
  13. 13. Reduction by Hydride Ion
  14. 14. Utilization of DIBAL to Control the Reduction Reaction
  15. 15. The reduction of a carboxylic acid with LiAlH4 forms asingle primary alcoholAcyl chloride is also reduced by LiAlH4 to yield an alcohol
  16. 16. An amide is reduced by LiAlH4 to an amine
  17. 17. Aldehydes and ketones react with a primary amine toform an imineThis is a nucleophilic addition–elimination reactionThe pH of the reaction must be controlled
  18. 18. Dependence of the rate of the reaction of acetone withhydroxylamine on the pH of the reaction: a pH rate profile
  19. 19. Aldehydes and ketones react with secondary amines toform enamines
  20. 20. Formation of Imine Derivatives
  21. 21. Deoxygenation of the Carbonyl Group
  22. 22. Water adds to an aldehyde or ketone to form a hydrate
  23. 23. Why is there such a difference in the Keq values?
  24. 24. The equilibrium constant for the reaction depends on therelative stabilities of the reactants and products
  25. 25. Addition of an Alcohol to an Aldehyde or a Ketone
  26. 26. Utilization of Protecting Groups in SynthesisLiAlH4 will reduce the ester to yield an alcohol, butthe keto group will also be reduced
  27. 27. The keto group is protected as a ketal in this synthesis
  28. 28. The more reactive aldehyde is protected with the diolbefore reaction with the Grignard reagent
  29. 29. • The OH group in an alcohol can be protected as a trimethylsilyl ether• The OH group in a carboxylic acid can be protected as an ester• An amino group can be protected with an acetyl group
  30. 30. Addition of Sulfur Nucleophiles
  31. 31. Desulfurization replaces the C–S bonds with C–H bonds
  32. 32. Formation of Alkenes The Wittig Reaction
  33. 33. Preparation of the Phosphonium YlideIf two sets of reagents are available for the synthesis ofan alkene, it is better to use the one that requires the lesssterically hindered alkyl halides
  34. 34. • The Wittig reaction is completely regioselective• This reaction is the best way to make a terminal alkene• Stable ylides form primarily E isomers, and unstabilized ylides form primarily Z isomers• Stable ylides have a group (C=O) that can share the carbanion’s negative charge
  35. 35. Stereochemistry of Nucleophilic Addition Reaction
  36. 36. • Nucleophiles that form unstable addition products formconjugated addition products, because the conjugateaddition is not reversible• Nucleophiles that form stable addition products can form direct addition products or conjugate addition products• If the rate of direct addition is slowed down by sterichindrance, a Grignard reagent will form the conjugateaddition product
  37. 37. Nucleophilic Addition to α,β-Unsaturated Carboxylic Acid Derivatives
  38. 38. Enzyme-Catalyzed Additions to α,β-Unsaturated Carbonyl Compounds

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