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Prerequisites: 112

today. Organic COURSE WEB PAGE. www.chem.sc.edu/faculty/bryson/index.html. . . . CHEM 333. . Prerequisites: 112. synthesis. 16. 8c. 8a. 8b. Chapter 8. Alkenes and Alkynes II: Addition Reactions. 59 ts.

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Prerequisites: 112

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  1. today Organic COURSE WEB PAGE www.chem.sc.edu/faculty/bryson/index.html    CHEM 333  Prerequisites: 112 synthesis 16 8c 8a 8b

  2. Chapter 8 Alkenes and Alkynes II: Addition Reactions 59 ts Powerpoint Slides - modified from the slides of Professor William Tam and Dr. Phillis Chang.

  3. CHAPTER 8 Alkenes and Alkynes II: Addition Reactions of enes Electrophilic addition of HX mechanism Markovnikov rule Stereochem of Ionic addition to enes Addition of H2SO4 Acid catalyzed addition of H2O ROH from enes-oxymercuration-DeHg ROH from hydroboration-oxidation Hydrobroation-alkylborane synthesis Oxidation & hydrolysis of alkylboranes Summary of Hydration Protonolysis of alkylboranes Ene electrophilic addition of Br2 & Cl2 Stereospecific rxs Halohydrin formation [divalent carbon - carbenes] Oxidative cleavage of alkenes syn 1,2-hydroxylation Oxidative cleavage of alkenes Ynes electrophilic addition of Br2 & Cl2 Addition of HX to ynes Oxidative cleavage of ynes Planning synthesis

  4.  +  bond +  bonds Addition Reactions of Alkenes E–Nuadds to  bond

  5. Electrophiles (acids) electron seeking Common Electrophiles: H+, X+ (X = Cl, Br, I), Hg2+, BH3, etc. C=C and C≡C -bonds (:Nu, :base) particularly reactive toward electrophiles

  6. Electrophilic (Markovnikov) Addition of HX to Alkenes: Mechanistic variations: bridged cation: (halonium ion, mercurinium ion) four centered transition state

  7. Markovnikov’s Rule - for unsymmetrical substrates 2 constitutional isomers are possible “regioisomers” different constitutional/regioisomers isomers

  8. Markovnikov’s Rule Electrophilic addition to an unsymmetrical olefin More highly stabilized carbocation is formed X note: carbocation stability  3o > 2o > 1o

  9. Addition of Hydrogen Halides Addition of HCl, HBr and HI across a C=C bond H+ is the electrophile

  10. Examples

  11. 2B. Modern Statement of Markovnikov’s Rule In the ionic addition of an unsymmetrical reagent to a double bond, the E+ attaches to a carbon of the double bond to yield the more stable carbocation intermediate

  12. Examples

  13. Examples

  14. Regioselective Reactions A reaction that could yield two or more constitutional isomers but produces only one (or a predominance of one), The reaction is regioselective

  15. Regioselective Reactions A reaction that could yield two or more constitutional isomers but produces only one (or a predominance of one), The reaction is regioselective

  16. Regio- and Stereo-chemistry of the Ionic Addition attack from top racemate achiral trigonal planar carbocation attack from bottom

  17. Addition of Water to Alkenes: Acid-Catalyzed Hydration Overall Addition of H–OH across a C=C bond H+ is the electrophile Markovnikov addition (dilute H2SO4, H3PO4) mechanism?

  18. Mechanism

  19. Alcohols from Alkyl Hydrogen Sulfates Overall result of sulfuric acid addition followed by hydrolysis is Markovnikov addition of H and OH

  20. Addition of Sulfuric Acid to Alkenes 3o not 1o carbocation

  21. Rearrangements

  22. Alcohols from Alkenes: Oxymercuration–Demercuration:(Markovnikov) Step 1: Oxymercuration Step 2: Demercuration mechanism?

  23. 6A. Regioselectivity of Oxymercuration–Demercuration Oxymercuration–demercuration is Markovnikov addition highly regioselective Mechanistic model: bridged cation: (mercurinium ion)

  24. No Rearrangements Carbocations can rearrange Oxymercuration no rearrangements

  25. 6C. Mechanism of Oxymercuration Does not undergo a “free carbocation”

  26. Stereochemistry anti-addition

  27. Solvomercuration-Demercuration R = H, alkyl

  28. Alcohols from Alkenes: Hydroboration–OxidationSyn Hydration Hydroboration BH3 complex with coordinative solvent (or dimer B2H6) mechanism?

  29. syn addition hydroboration-oxidation

  30. syn addition hydroboration-oxidation Ch. 8 - 30

  31. 8A. Mechanism of Hydroboration

  32. Oxidation Hydrolysis

  33. + [Na3BO3] Oxidation mechanism/formalism Ch. 8 - 33

  34. Overall: “anti-Markovnikov” addition of H–OH oxidation occurs with retention of configuration   Opposite regioisomers as oxymercuration-demercuration

  35. Protonolysis of Alkylboranes hydrogen replaces boron with retention of configuration

  36. acetylene hydroboration the same as olefins R = H, alkyl

  37. enol unstable Terminal acetylene hindered or dialkylborane (HBR2) preferred tautomerism: H+transfer (O to C, C to O)

  38. Oxymercuration

  39. Hg++/H2O ketone internal yne: “either”  ketone(s) Hydration of acetylenes terminal yne: HBR2/[O]aldehyde

  40. enol-keto tautomerism H+ transfer C  O from HB/[O] Hg+2/H2O other rxs mechanism e(-) arrows or

  41. Summary of Alkene Hydration Methods rearrangement Markovnikov addition “anti-Markovnikov,” syn addition of H2O

  42. Protonolysis of Alkylboranes hydrogen replaces boron with retention of configuration Overall stereochemistry of hydroboration–protonolysis: syn

  43. Anti Addition of Halide to Alkenes Addition of X–X (X = Cl, Br, and I) across a C=C bond mechanism?

  44. 12A. Mechanism of Halogen Addition (bromonium) Br–Br bond becomes polarized when close to alkene

  45. Stereochemistry Anti addition + enantiomer

  46. Stereospecific: A reaction is stereospecific when a stereoisomeric compound reacts forming a specific stereoisomeric form Why? Ch. 8 - 46

  47. Reaction 1 Reaction 2

  48. trans-2-butene: anti addition, bromonium ion (a) (b)

  49. cis-2-butene (a) (b)

  50. regiochemistry  on NuE & substituents rearrangements stereochemistry stereochemistry Types of Electrophilic (Markovnikov) Addition to Alkenes: free carbocation bridged cation: anti addition (halonium ion, mercurinium ion) syn addition four centered transition state Ch. 8 - 50

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