1 / 32

Alkenes II-continued 1. Types of Rxn.: elimination, addition, substitution

Alkenes II-continued 1. Types of Rxn.: elimination, addition, substitution 2. Mechanisms: How rxn’s of molecules occur. 3. Electrophilic (Markovnikov) addition A. Addition of HX, regioselective R 3 C + > R 2 HC + > RH 2 C + > H 3 C + B. Hydration H + /H 2 O C. Rearrangements

Download Presentation

Alkenes II-continued 1. Types of Rxn.: elimination, addition, substitution

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. Alkenes II-continued 1. Types of Rxn.: elimination, addition, substitution 2. Mechanisms: How rxn’s of molecules occur. 3. Electrophilic (Markovnikov) addition A. Addition of HX, regioselective R3C+ > R2HC+ > RH2C+ > H3C+ B. Hydration H+/H2O C. Rearrangements D. Bromonium ions, (anti addition) E. Halohydrin formation, (anti) F. H+ - hydration, Hg+2-hydration - (anti) 4. Hydroboration (syn addition) 5. Oxidation (syn) 6. Reduction (syn), olefin and diene stability 7. Reactions relative to stereocenters For PRACTICE (“worksheet”) problems go to the home page Work/Study Sheet 6 due in recitation 3/26 or 3/27 SS! 28 19

  2. Chapter 6 synthesis reaction types olefin additions mechanisms energy progress of rx specific additions and reactions

  3. Chapter 6 synthesis hydration rearrangements hydroboration other additions stereochemistry halogenation halohydration mercury hydration

  4. H H OH C C R H R H C C H H H F. Alternative “Hydration” of Alkenes Oxymercuration/Reduction Hg(OAc)2 NaBH4 + Hgo +HOAc H2O R = H, alkyl, Ph, etc. 2 rx sequence

  5. Last lecture:

  6. Last lecture: 3o>2o

  7. “general” antiaddition

  8. 1 2 Issues: no rearrangement regiochemistry stereochemistry

  9. Issues: rearrangement regiochemistry stereochemistry

  10. NaBH4 H Na H B H ~[ :H(-)] H [1] Issues: rearrangement regiochemistry stereochemistry [2]

  11. 6.4 HYDROBORATION [ BH or B H ] 3 2 6 +  H   H B H 2 B H H H H CH CH 3 3 mechanism: syn addition H moves with 2 electrons [H:](-)  H H B H (+) H CH 3 

  12. 6.4 HYDROBORATION [BH3 or B2H6] rx [ts] synchronous B& H addition

  13. OXIDATION synchronous B & H addition 6.4 HYDROBORATION / rx ts

  14. OXIDATION 6.4 HYDROBORATION / rx

  15. Note regioselectivity H OH H BH2 H H BH3 H2O2 H H C C H H C C C C NaOH ether H R H H R R Hg(OAc)2 NaBH4 H2O OH H H H H H C C C C H H R R H+ H2O

  16. Hydroxylation [O] of olefins Note: cold KMnO4/(-)OH = OsO4/ROOH/H2O

  17. mechanism: syn addition of O’s H2O ROOH isoelectronic cold/basic/H2O

  18. H C 3 CH C 3 O H C 3 CH + C 3 O H C C 3 H C C 3 note! H H H2O2 H C 3 CH C 3 O + O H C C 3 OH Ozonolysis reducing agent S(CH3)2 (or Zn:) + O3 oxidizing reagent mechanism: syn addition,ignore H oxidized to OH

  19. Ozonolysis

  20. metal surface H H H H H H R R C C R R R C C R R R R R C C R R Catalytic addition of H2 to  bonds break one C-C bond, gain two C-H bonds How? H2

  21. H2

  22. other double bonds Catalytic addition of H2 to  bonds

  23. H H R C H R R C C < C H H C < C R H C H H H C H R H R C R R C < C R R H R C < C H R C R R R R H H metal C C C C  + H + cat. H 2 H H H H H H stability of olefins (based on energy released)

  24. 60.6 kcal -56.5 kcal ~60.6 kcal ~56.5 kcal 4.1 kcal Conjugated Dienes - similar to simple olefins but resonance makes them special. Classification: isolated conjugated resonance energy

  25. Reaction: conjugated vs unconjugated 1 equivalent Br2 1 equivalent Br2 + “1,4-addition” vs “1,2-addition”

  26. Stereochemistry of Reactions regio constitutional isomers selective specific excess of product X over Y only product X, no Y (product X’s, no Y’s) stereo stereoisomers

  27. 100% 0% Stereochemistry of Reactions Regioselectiverx - of 2 possible constitutional isomers, rx forms 1 > other (Markovnikov addition). 30 | 70 Regiospecificrx - of 2 possible constitutional isomers, rx forms 1 (Markovnikov addition).

  28. Stereospecific rx stereoisomers  stereoisomers products

  29. Stereoselectiverx: Rx stereoisomer [B] > [C] major

  30. equal opportunityeither side Review Rx forming stereogenic center - ionic addition: 7 regiospecific not stereo-selective or -specific

  31. Br- Review: Br2, Cl2, I2, Hg++ - anti addition 7

  32. OsO4, KMnO4, HBR2, H2 , O3 - syn addition No RR ionic addition - carbocations - possible RR racemic 7

More Related