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Understanding Ketones and Aldehydes: Nomenclature, Properties, and Synthesis Techniques

This chapter provides a comprehensive overview of ketones and aldehydes, two important classes of carbonyl compounds. It covers nomenclature rules for naming these compounds, their unique properties including boiling points and solubility, and techniques for their synthesis, such as Grignard reactions and oxidation methods. Additionally, the chapter discusses key spectroscopic techniques for characterization, including IR and NMR spectroscopy, as well as various industrial applications of these compounds. Key reactions and mechanisms are also highlighted for a better understanding of their chemical behavior.

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Understanding Ketones and Aldehydes: Nomenclature, Properties, and Synthesis Techniques

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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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