Orgo 8.4, 8.5, 8.7

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Orgo 8.4, 8.5, 8.7
2013-11-20 22:06:43
CHM 201

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  1. An alkene may react with water in the presence of a strongly __ to form an __. Formally, this reaction is a __, with a H atom adding to one carbon and a hydroxygl group adding to the other.
    • acidic catalyst
    • alcohol
    • hydration
  2. Hydration of an alkene is the reverse of the __.
    dehydration of alcohols
  3. For dehydrating alcohols, a concentrated dehydrating acid is used to __. Hydration of an alkene, on the other hand, is accomplished by doing what?
    • drive the equilibrium to favor the alkene
    • adding excess water to drive the equilibrium toward the alcohol
  4. What does the principle of microscopic reversibility state?
    that a forward reaction and a reverse reaction taking place under the same conditions must follow the same reaction pathway in microscopic detail
  5. The __ and __ reactions are the two complementary reactions in an equilibrium; therefore, they must follow the same reaction pathway. It makes sense that the __ and intermediates for the reverse reaction are the same as those for the forward reaction, except in reverse order.
    • hydration ad dehydration reactions
    • lowest energy TS
  6. Acid-catalyzed hydration of an alkene
    • 1: protonation of the double bond forms a carbocation
    • 2: nucleophilic attack by water gives a protonated alcohol
    • 3: deprotonation gives the alcohol
  7. Step one of the hydration mechanism is similar to the first step in the __. The proton adds to the __ to form the __ subbed carbocation. __ attacks the carbocation to give (after the loss of a proton) the alcohol with the --OH group
    • addition of HBr
    • less subbed end of hte double bond
    • more 
    • Water
  8. Like the addition of Hydrogen halides, hydration is __. It follows __, giving a product in which the new hydrogen has added to the __ of hte double bond.
    • regioselective
    • Mark's rule
    • less subbed end
  9. The proton adds to the __, so the positive charge appears at the __ end. Water attacks the __ to give the __.
    • less subbed end of the double bond
    • more subbed
    • carbocation
    • protonated alcohol
  10. The reaction follws __. The proton has added to the end of the double bond that already had more __, and the --OH to the __. Hydration may take place with __.
    • Mark's rule
    • hydrogens
    • more subbed end
    • rearrangement
  11. Many alkenes do not easily undergo __ in aqueous acid. Some alkenes are nearly __ in aqueous acid, and oters undergo side reactions, such as __, __, or __ under these strongly acidic conditions. In some cases, the overall equilibrium favors the __ rather than the alcohol. No amount of __ can cause a reaction to occur if the __ are unfavorable.
    • hydration
    • insoluble
    • rearrangement 
    • polymerization
    • charring 
    • alkene
    • catalysis
    • energetics
  12. __ is another method for converting alkenes to alcohols with __. __ works with many alkenes that do not easily undergo direct __, and it takes place under milder conditions. No free __ is formed, so there is no opportunity for __ or __.
    • oxymercuration-demercuration
    • Markovnikov orientation
    • Oxymercuration-demercuration
    • hydration
    • carbocation
    • rearrangements 
    • polymerization
  13. The reagent for mercuration is __. How does it act as an electrophile?
    • mercuric acetate Hg(OAc)2
    • the simplest one is that mercuric acetate dissociates slightly to form a positively charged mercury species
  14. __ involves an electrophilc attack on the double bond by the positively charged mercury species. THe product is a __, an organometallic cation containing a three-membered ring. In the second step, water from the solvent attacks the __to give (after deprotonation) an __.
    • oxymercuration
    • mercurinium ion 
    • organomercurial alcohol
  15. A subsequent reaction is __ to remove the mercury. Sodium borohydride replaces the __ with a hydrogen atom.
    • demercuratoin
    • mercuric acetate
  16. Oxymercuration of an alkene
    • 1) electrophilic attack forms a mercurinium ion
    • 2) water opens the ring to give an organomercurial alcohol; demercuration replaces the mercuric fragment with hydrogen to give the alcohol
  17. __ of an unsymmetrical alkene generally gives __. The __ has a considerable amt. of positive charge on both of its carbon atoms, but there is more of a positive charge on the __, where it is more stable.
    • oxymercuration-demercuration
    • Markovnikov orientation of addition
    • mercurinium ion
    • more subbed carbon atom
  18. Attack by water occurs on this more __ carbon, giving __. The electrophile, __, remains bonded to the __. __ of the __ gives the __.
    • electrophilic
    • Markovnikov orientation
    • +Hg(OAc)
    • less subbed end of hte double bond
    • reduction
    • organomercurial alcohol
    • Markovnikov alcohol
  19. __ reliably adds water across the double bond of an alkene with __ and without __.
    • oxymercuration-demercuration
    • Markovnikov orientation
    • rearrangement
  20. Why is oxymercuration-demercuration most commonly used in lab?
    it gives better yields than direct acid-catalyzed hydration, it avoids the possibility of rearrangements, and it does not involve harsh conditions
  21. What is the downside of oxymercuration-demercuration?
    it is highly toxic
  22. What if we need to convert an alkene to the anti-Mark alcohol?
    we use the hydroboration of alkenes
  23. Such an __ was iimpossible until H.C. Brown discovered that __ adds to alkenes with __ to form __, which can be oxidized to give __.
    • anti-Mark hyydration
    • diborane
    • anti-Mark orientation
    • alkylboranes
    • anti-Mark alcohols
  24. __ is a dimer composed of two molecules of borane. The bonding in __ is unconventional, using three-centerd bonds with protons in the middle of them. __ is in equilibrium with a small amount of borane, a strong Lewis acid with only six valence electrons.
    • diborane
    • diborane
    • diborane
  25. __ is an inconvenient reagent becuase it is a toxic, flammable, and explosive gas. It is more easily used as a complex with __, a cyclic ether. The complex reacts like diborane, yet the solution is easily measured and transferred.
    • diborane
    • THF (tetrahydrofuran)
  26. The Bf3⋅THF reagent is the form of borane commonly used in organic reactions. BH3 adds to the __ of an alkene to give an __. Basic hydrogen peroxide oxidizes the __to an alcohol. In effect, __ converts alkenes to alcohols by adding water across the double bond, with __
    • double bond
    • alkylborane
    • alkylborane 
    • hydroboration-oxidation
    • anti-Mark orientation.
  27. Borane is an electron-deficient compound. It has only __, so the boron atom in BH3 cannot have an __. 
    __ is the driving force for the unusual bonding structures found in boron compounds. As an __ compound, BH3 is a strong __, capable of adding to a double bond. The __ of the double bond is thought to occur in one step, with the boron atom adding to the less subbed end of the double bond.
    • six valence electrons
    • octet
    • acquiring an octet
    • electron-deficient
    • electrophile
    • hydroboration
  28. In the __, the __ boron atom withdraws electrons from the pi bond, and the carbon at the other end of hte double bond acquires a __. This __ is more stable on the __ carbon atom.
    • transition state
    • electrophilic
    • partial positive charge
    • partial charge
    • more subbed carbon atom
  29. The product shows boron bonded to the __ end of the double bond and hydrogen bonded to the __. Also, __ favors boron adding to the less hindered, less subbed end of the double bond.
    • less subbed 
    • more subbed end
    • steric hindrance
  30. Hydroboration of an Alkene
    Borane adds to the double bond in a single step. Boron adds to the less hindered, less subbed carbon, and hydrogen adds to the more subbed carbon
  31. The boron atom is removed by __, using aqueous sodium hydroxide and hydrogen peroxide to replace the boron atom with a __. The __ does not affect the orientation of the product, because the __ was established int he first step, the addition of BH3.
    • oxidation
    • hydroxyl group
    • oxidation
    • anti-Markovnikov orientation
  32. This hydration of an alkene by __ is another example of a reaction that does not follow the original statement of __ rule (the product is __), but still follows our understanding of the reasoning behind __. The electrophilic boron atom adds to the __ end of hte duoble bond, placing the positive charge (and the hydrogen atom) at the __ end.
    • hydroboratio-oxidation
    • Markovnikov's rule
    • anti-Markovnikov
    • Markovnikov's rule
    • less subbed 
    • more subbed
  33. Each B-H bond in BH3 can add across the double bond of an alkene. THe firs addition forms an __, the second a __, and the third a __.
    • alkylborane
    • dialkylborane
    • trialkylborane
  34. __ react exactly as we have discussed, adn they oxidize to give __. __ are quite bulky, further reinforcing the preference for boron to add to the elss hindered carbon atom of the double bond.

    Boranes are drawn as the 1:1 __  to simplify their structure and emphasize the organic part of the molecule.
    • trialykboranes
    • anti-Mark alcohols
    • Trialkylboranes
    • monoalkylboranes
  35. The simultaneous addition of boron and hydrogen to teh double bond elads to a __: Boron and H add across the double bond on the __. (If they added to opposite sides, the process would be an __)
    • syn addition 
    • same side of hte molecule
    • anti addition
  36. What is expected with hydroboration? (of the example with oxidation of the trialkylborane)
    a racemic mixture because the chiral product is formed from achiral reagents
  37. What is the second step of hydroboration?
    oxidation of the borane to the alcohol
  38. Hydroboratoin of alkenes is another example of a __, in which different stereoisomers of the starting compound react to give different stereoisomers of the product.
    stereospecific reaction
  39. Steps of hydroboration with hydroperoxide
    • 1) formation of hte hydroperoxide ion
    • 2) addition of hydroperoxide nad migration of the alkyl gorup
    • 3) twice more to oxidize the other two alkyl groups
    • 4) hydrolysis of the borate ester