1 / 25

Chapter 18: Enols and Enolates

Chapter 18: Enols and Enolates. Overview. Enols : Enolates :. 18.1 – The a Hydrogen and Its p Ka. 18.2 – The Aldol Condensation. When appropriate base is used, both aldehyde and enolate present in solution, this leads to the aldol reaction. 18.2 – The Aldol Condensation (loss of H 2 O).

azura
Download Presentation

Chapter 18: Enols and Enolates

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 18: Enols and Enolates Overview Enols : Enolates :

  2. 18.1 – The a Hydrogen and Its pKa

  3. 18.2 – The Aldol Condensation When appropriate base is used, both aldehyde and enolate present in solution, this leads to the aldol reaction

  4. 18.2 – The Aldol Condensation (loss of H2O) When the reaction is run at low temperature the aldol product may be isolated; at elevated temperature the elimination occurs

  5. 18.3 – Mixed (Crossed) Aldol Reactions 2 enolizable substrates leads to multiple products all present in solution at same time

  6. 18.3 – Mixed (Crossed) Aldol Reactions Usually use 1 non-enolizable substrate: Elimination of H2O common when conjugation results, can also be induced by heating the reaction mixture

  7. 18.4 – Alkylation of Enolate Ions

  8. Staphylococcus aureus (MRSA, VRSA) • Greek staphyle meaning “a bunch of grapes” • Greek kokkos meaning “berry” • aureus = yellow

  9. Gram-positive, cluster-forming coccus • Cause food poisoning, endocarditis, osteomyelitis • Can cause septiceamia, infections on implants • Becoming increasingly resistant to antibiotics • MRSA strains appeared in 1961 • VRSA first reported in the USA in 2002

  10. Microcapsule (carbohydrate) – defends against phagocytosis

  11. Bacterial Capsular Polysaccharides – serotypes

  12. 18.5 – Enolization and Enol Content Tautomers – two structures that differ by placement of an atom or a group The enol formis usually in low concentration since the C=O is more stable Tautomerismis acid-catalyzed and base-catalyzed

  13. 18.5 – Enolization and Enol Content

  14. 18.5 – Base-Catalyzed Enolization Enolate resonance forms – not tautomers

  15. 18.5 – Acid-Catalyzed Enolization Sequential proton transfers

  16. 18.6 – Stabilized Enols

  17. 18.7 – a-Halogenation of Aldehydes and Ketones • The reaction overall is a substitution • The reaction is regiospecific – only a-H is replaced

  18. 18.8 – Mechanism of a-Halogenation of Aldehydes and Ketones Very good cation generated (hetero-atom stabilized)

  19. 18.9, 18.10 – The Haloform Reaction and a-Deuteration Iodoform reaction iodoform A methyl ketone a-Deuteration

  20. 18.11 – Conjugation in a,b-Unsaturated Systems Carbonyl carbon andb-carbon have positive character Acrolein Figure 18.2 Pi system is completely delocalized

  21. 18.12 – Conjugate Addition to a,b-Unsaturated Systems More reactive nucleophiles (e.g. RMgX) attack the most +ve C i.e. the carbonyl carbon. These reactions are usually irreversible. Softer nucleophiles undergo reversible addition and lead to the more stable (thermodynamically favoured) 1,4-addition product.

  22. 18.13 – The Michael Reaction H alpha to two C=O will be more acidic than next to one C=O, deprotonation leads to a soft nucleophile that adds 1,4-

  23. 18.13 – Michael Addition – Robinson Annulation Sequence Application:

  24. 18.14 – Conjugate Addition of Organocopper Reagents

More Related