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Chapter 18 : Ketones and Aldehydes

Chapter 18 : Ketones and Aldehydes. Classes of Carbonyl Compounds. Carbonyl. C=O bond is shorter, stronger and more polar than C=C bond in alkenes. Nomenclature: Ketone. Number chain so the carbonyl carbon has the lowest number Replace “e” with “one”. Nomenclature: Cyclic Ketone.

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Chapter 18 : Ketones and Aldehydes

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  1. Chapter 18: Ketones and Aldehydes

  2. Classes of Carbonyl Compounds

  3. Carbonyl • C=O bond is shorter, stronger and more polar than C=C bond in alkenes

  4. Nomenclature: Ketone • Number chain so the carbonyl carbon has the lowest number • Replace “e” with “one”

  5. Nomenclature: Cyclic Ketone • Carbonyl carbon is #1

  6. Nomenclature: Aldehydes • Carbonyl carbon is #1 • Replace “e” with “al” • If aldehyde is attached to ring, suffix “carbaldehyde” is used

  7. Nomenclature • With higher-priority functional groups, ketone is “oxo” and an aldehyde is a “formyl” group • Aldehydes have higher priority than ketones

  8. Nomenclature- Common Names: Ketones • Name alkyl groups attached to carbonyl • Use lower case Greek letters instead of numbers

  9. Nomenclature

  10. Boiling Points • Ketones and aldehydes are more polar. Have higher boiling point that comparable alkanes or ethers

  11. Solubility: Ketones and Aldehydes • Good solvent for alcohols • Acetone and acetaldehyde are miscible in water

  12. Formaldehyde • Gas at room temperature

  13. IR Spectroscopy • Strong C=O stretch around 1710 cm-1 (ketones) or 1725 cm-1 (simple aldehydes) • C-H stretches for aldehydes: 2710 and 2810 • cm-1

  14. IR Spectroscopy • Conjugation lowers carbonyl frequencies to about 1685 cm-1 • Rings with ring strain have higher C=O frequencies

  15. Proton NMR Spectra • Aldehyde protons normally around δ9-10 • Alpha carbon around δ2.1-2.4

  16. Carbon NMR Spectra

  17. Mass Spectrometry (MS)

  18. Mass Spectrometry (MS)

  19. Mass Spectrometry (MS)

  20. McLafferty Rearrangement • Net result: breaking of the , bond and transfer of a proton from the  carbon to oxygen

  21. Ultraviolet Spectra of Conjugated Carbonyls • Have characteristic absorption in UV spectrum • Additional conjugate C=C increases max about 30 nm, additional alkyl groups increase about 10nm

  22. Carbonyl Electronic Transitions

  23. Industrial Uses • Acetone and methyl ethyl ketone are common solvents • Formaldehyde is used in polymers like Bakelite and other polymeric products • Used as flavorings and additives for food

  24. Industrial Uses

  25. Synthesis of Aldehydes and Ketones • The alcohol product of a Grignard reaction can be oxidized to a carbonyl

  26. Synthesis of Aldehydes and Ketones • Pyridiniumchlorochromate (PCC) or aSwern oxidation takes primary alcohols to aldehydes

  27. Synthesis of Aldehydes and Ketones • Alkenes can be oxidatively cleaved by ozone, followed by reduction

  28. Synthesis of Aldehydes and Ketones • Friedel-Crafts Acylation

  29. Synthesis of Aldehydes and Ketones • Hydration of Alkynes • Involves a keto-enoltautomerization • Mixture of ketones seen with internal alkynes

  30. Synthesis of Aldehydes and Ketones • Hydroboration-oxidation of alkyne • Anti-Markovnikov addition

  31. Synthesis Problem

  32. Synthesis of Aldehydes and Ketones • Organolithium + carboxylic acid ketone (after dehydration)

  33. Synthesis of Aldehydes and Ketones • Grignard or organolithium reagent + nitrile  ketone (after hydrolysis)

  34. Synthesis of Aldehydes and Ketones • Reduction of nitriles with aluminum hydrides will afford aldehydes

  35. Synthesis of Aldehydes and Ketones • Mild reducing agent lithium aluminum tri(t-butoxy)hydride with acid chlorides

  36. Synthesis of Aldehydes and Ketones • Organocuprate (Gilman reagent) + acid chloride  ketone

  37. Nucleophilic Addition • Aldehydes are more reactive than ketones

  38. Wittig Reaction • Converts the carbonyl group into a new C=C bond • Phosphorusylide is used as the nucleophile

  39. Wittig Reaction • Phosphorusylides are prepared from triphenylphosphine and an unhindered alkyl halide • Butyllithium then abstracts a hydrogen from the carbon attached to phosphorus

  40. Wittig Reaction- Mechanism • Betaine formation • Oxaphosphetane formation

  41. Wittig Reaction- Mechanism • Oxaphosphetane collapse

  42. How would you synthesize the following molecule using a Wittig Reaction

  43. Hydration of Ketones and Aldehydes • In aqueous solution, a ketone or aldehyde is in equilibrium with it’s hydrate • Ketones: equilibrium favors keto form

  44. Hydration of Ketones and Aldehydes • Acid-Catalyzed

  45. Hydration of Ketones and Aldehydes • Base-Catalyzed

  46. Cyanohydrin Formation • Base-catalyzed nucleophilic addition • HCN is highly toxic

  47. Formation of Imines • Imines are nitrogen analogues of ketones and aldehydes • Optimum pH is around 4.5

  48. Formation of Imines- Mechanism

  49. Condensations with Amines

  50. Acetal Formation

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