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Revision Session

Revision Session. Organic Chemistry. Stereochemistry and mechanism . Starter Past Paper Questions and Answers. Aromaticity. Starter Past Paper Questions and Answers. Question 1 (a) Huckel’s Rule Discuss [100%]. Aromatics. Revision and Past Paper Questions and Answers.

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Revision Session

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  1. Revision Session Organic Chemistry

  2. Stereochemistry and mechanism Starter Past Paper Questions and Answers

  3. Aromaticity Starter Past Paper Questions and Answers

  4. Question 1 (a) Huckel’s Rule Discuss [100%]

  5. Aromatics

  6. Revision and Past Paper Questions and Answers Carbonyl Group Chemistry

  7. Basic Carbonyl Chemistry • Carbonyl acts as both an electrophileand anucleophile • Carbonyl has resonance structure

  8. Basic carbonyl chemistry Electrophile:

  9. Basic carbonyl chemistry Formation of Enolates and Enols Removal of alpha-proton (most acidic)

  10. Basic carbonyl chemistry Enolate Alkylation Nucleophile

  11. Basic carbonyl chemistry Acidities of alpha and beta carbonyl protons

  12. Basic carbonyl chemistry 1,3 – Dicarbonyl Compounds Why is central alpha proton more acidic? Conjugation and intramolecular H – bonding

  13. Basic carbonyl chemisty Alpha substitution reactions Reaction with an electrophile (acid catalysed)

  14. Basic carbonyl chemistry Alpha substitution reactions Reaction with an electrophile (base catalysed)

  15. Basic carbonyl chemistry Bases used for enolate formation Carbonyl compounds weakly acidic Strong baseneeded to ensure complete enolate formation LDA Lithium diisopropylamide

  16. Basic carbonyl chemistry Deuterium Substitution of alpha protons When enriched with D2O (acid or base), all alpha protonsare in equilibria with deuterium Used as an isotopic label in molecules

  17. Basic carbonyl chemistry Racemization Stereochemistry at alpha carbon is lost during enolate formation Protonated unequally at two faces

  18. Basic Carbonyl CHemistry Halogenation of Carbonyls (acid catalysed)

  19. Basic carbonyl chemistry Halogenation of Carbonyls (lewis acid)

  20. Basic carbonyl chemistry Unsymmetrical Ketones Two different enolsare formed Occurs preferentially at the more substitutedposition as more stable

  21. Basic carbonyl chemistry Enolates of Unsymetrical Ketones Kinetic favoured due to unhindered alpha protons

  22. Basic carbonyl chemistry 1,3 – Dicarbonyl Compounds Alkylate at different sites in different conditions

  23. Basic carbonyl chemistry Decarboxylation of beta-ketoesters

  24. Basic carbonyl chemistry Add a -CH2CO2H to an alkyl halide

  25. Basic carbonyl chemistry Add a -CH2COCH3 to an alkyl halide

  26. Basic carbonyl chemistry Add a -CH2CO2H then –COCH3 to an acyl halide

  27. Aldol reaction https://learn.uea.ac.uk/webapps/portal/frameset.jsp?tab_tab_group_id=_4_1&url=%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Ftype%3DCourse%26id%3D_85894_1%26url%3D Click Vignettes – Level 1 – Aldol Reaction

  28. Basic carbonyl chemistry Aldol Reaction Mixed Aldol Reaction Use LDA (one equivalent) to convert all of aldehyde to enolate Same Ketone Aldol Reaction Use NaOEt/EtOHto convert a small proportion to enolate

  29. Basic carbonyl chemistry Aldol Dehydration Base Catalysed Acid Catalysed (more common)

  30. Basic carbonyl chemistry Intramolecular Aldol Reactions Dicarbonyl compounds treated with base Leads to cyclic product

  31. Basic carbonyl chemistry Intramolecular Aldol Reactions For Unsymmetrical Dicarbonyl Species more than one product is possible

  32. Basic carbonyl chemistry Claisen Condensation Esters react in same fashion as aldol reaction Intramolecular Claisen Condensations aswell

  33. Basic carbonyl chemistry Knoevenagel Condensation

  34. Basic carbonyl chemistry Michael Reaction Enolates react with conjugated carbonyls through terminus double bonds rather than the carbonyl itself!

  35. Robinson Annelation Micheal reaction followed by intramolecular aldol Micheal Addition Intramolecular Aldol Aldol Condensation (Base catalysed)

  36. Basic carbonyl chemistry Condensation with Amine Derivatives Ketone  Imine

  37. Basic carbonyl chemistry Condensation with Amine Derivatives Imine  Enamine

  38. Basic carbonyl chemistry Enamine Reactivity React simular to enolatesin neutral form. Forms iminium salt, hydrolysis leads to alkylated carbonyl

  39. basic carbonyl chemistry Enamine Reactivity

  40. Basic carbonyl chemistry Wittig Reaction Introduces alkenes from ketones using phosphorus ylids.

  41. Wittig reaction Stage 1 Preparation of a phosphonium salt from an alkyl halide

  42. Wittig reaction Stage 2 Deprotonation of the phosphonium salt to form a ylid

  43. Wittig reaction Stage 3 Reaction of the ylid with a carbonyl group

  44. Wittig reaction E or Z alkenes? Ylids that have a conjugatingor anion-stablilizing substituent (such as a carbonyl) adjacent to negative charge give E – Alkenes Ylids without such groups are unstabilizedylidsand tend to give Z – Alkenes

  45. Wittig reaction Example of Z – Alkene formation Example of E – Alkene formation

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