1 / 100

Chapter 16

Chapter 16. Aldehydes & Ketones: Nucleophilic Addition to the Carbonyl Group. Introduction. Carbonyl compounds. Nomenclature of Aldehydes & Ketones. Rules: Aldehyde as parent (suffix) Ending with “ al ”; Ketone as parent (suffix) Ending with “ one ”.

kirsi
Download Presentation

Chapter 16

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 16 Aldehydes & Ketones: Nucleophilic Addition to the Carbonyl Group

  2. Introduction • Carbonyl compounds

  3. Nomenclature of Aldehydes &Ketones • Rules: • Aldehyde as parent (suffix) • Ending with “al”; • Ketone as parent (suffix) • Ending with “one”. • Number the longest carbon chain containing the carbonyl carbon and starting at the carbonyl carbon.

  4. Examples:

  5. group as a prefix: methanoyl or formyl group • group as a prefix: ethanoylor acetyl group (Ac) • groups as a prefix: alkanoylor acyl groups

  6. Physical Properties • Comparison:

  7. Synthesis of Aldehydes 4A. Aldehydes by Oxidation of 1oAlcohols:

  8. e.g.

  9. 4B. Aldehydes by Ozonolysis ofAlkenes:

  10. e.g.

  11. 4C. Aldehydes by Reduction of AcylChlorides, Esters, and Nitriles: Not a good method for aldehydes. LiAlH4 is to reactive.

  12. LiAlH4 is a very powerful reducing agent, and aldehydes are easily reduced. • Usually reduced all the way to the corresponding 1o alcohol. • Difficult to stop at the aldehyde stage. • Using LiAlH4 is not a good method to synthesize aldehydes.

  13. Two derivatives of aluminum hydride that are less reactive than LiAlH4. • These are effective where LiAlH4 is not. For acid chlorides For esters and nitriles

  14. Aldehydes from acyl chlorides: RCOCl RCHO: • e.g.

  15. Reduction of an Acyl Chloride to an Aldehyde

  16. Aldehydes from esters and nitriles: • RCO2R’ RCHO RC≡N RCHO • Both esters and nitriles can be reduced to aldehydes by DIBAL-H.

  17. Reduction of an ester to an aldehyde:

  18. Reduction of a nitrile to an aldehyde:

  19. Examples:

  20. Synthesis of Ketones 5A. Ketones from Alkenes, Arenes,and 2o Alcohols: • Ketones (and aldehydes) by ozonolysis of alkenes.

  21. Examples:

  22. Ketones from arenes by Friedel–Crafts acylations.

  23. Ketones from secondary alcohols by oxidation.

  24. 5B. Ketones from Nitriles:

  25. Examples:

  26. Suggest synthesis of: from and

  27. 5 carbons here 4 carbons here • Retrosynthetic analysis:  need to add one carbon

  28. disconnection disconnection • Retrosynthetic analysis:

  29. Synthesis:

  30. Suggest synthesis of: from and

  31. 5 carbons here 5 carbons here • Retrosynthetic analysis:  no need to add carbon

  32. disconnection • Retrosynthetic analysis:

  33. Synthesis

  34. Nucleophilic Addition to theCarbon–Oxygen Double Bond • Structure: Nu⊖ • Carbonyl carbon: sp2 hybridized • Trigonal planar structure

  35. Polarization and resonance structure: • Nucleophiles will attack the nucleophilic carbonyl carbon. • Note: nucleophiles usually do not attack non-polarized C=C bond.

  36. With a strong nucleophile:

  37. Also would expect nucleophilic addition reactions of carbonyl compounds to be catalyzed by acid (or Lewis acid). • Note: full positive charge on the carbonyl carbon in one of the resonance forms. • Nucleophiles readily attack.

  38. Mechanism:

  39. Mechanism:

  40. 6A. Reversibility of NucleophilicAdditions to the Carbon–OxygenDouble Bond • Many nucleophilic additions to carbon–oxygen double bonds are reversible; the overall results of these reactions depend, therefore, on the position of an equilibrium.

  41. 6B. Relative Reactivity: Aldehydesvs. Ketones

  42. small large • Steric factors:

  43. Electronic factors: (positive inductive effect from both R & R' groups)  carbonyl carbon less d+ (less nucleophilic) (positive inductive effect from only one R group)

  44. The Addition of Alcohols:Hemiacetals and Acetals • Acetal & Ketal Formation: Addition of Alcohols to Aldehydes: Catalyzed by acid

  45. Mechanism:

  46. Mechanism (Cont’d):

  47. Mechanism (Cont’d):

  48. Note: All steps are reversible. In the presence of a large excess of anhydrous alcohol and catalytic amount of acid, the equilibrium strongly favors the formation of acetal (from aldehyde) or ketal (from ketone). • On the other hand, in the presence of a large excess of H2O and a catalytic amount of acid, acetal or ketal will hydrolyze back to aldehyde or ketone. This process is called hydrolysis.

More Related