Orgo 8.8-8.10

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Orgo 8.8-8.10
2013-11-18 20:28:47
CHM 201

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  1. halogens add to alkenes to form __. 
    A halogen molecule is __; a nucleophile can react with a halogen, displacing a __.
    • vicinal dihalides
    • electrophilic
    • halide ion
  2. In some reactions, the pi electrons of an alkene attack the bromine molecule, doing what? A __ results, containing a 3-membered ring with a positive charge on the bromine atom. This __ is similar to the __. Similar reactions with other halogens form other __. The structures of a __, a __, and an __ also exist.
    • expelling bromide ion
    • bromonium ion x
    • mercurinium ion
    • halonium ions
    • chloronium ion
    • bromonium ion
    • iodonium ion
  3. Unlike a normal carbocation, all the atoms in a halonium ion have __.
    The three-membered ring has considerable __, which, combined with a ositive charge on an electronegative halogen atom, makes the __ strongly electrophilic. Attack by a nucleophile does what?
    • filled octets
    • ring strain
    • halonium ion
    • opens the halonium ion to give a stable product
  4. Addition of Halogens to Alkenes
    • 1) electrophilic attack forms a halonium ion
    • 2) the halide ion opens the halonium ion
  5. Cl and Br commonly add to alkenes by the __. Iodination is used less frequently because __ products decompose easily. Any solvents used must be __ to the halogens; methylene chloride, chloroform, and carbon tetrachloride are the most frequent choices
    • halonium ion mechanism
    • diiodide products
    • inert
  6. The addition of bromine to cyclopentene is a stereospecific __.
    anti addition
  7. __ results from the bromonium ion mechanism. When a nucleophile attacks a __, it must do so from the __, assuring __.
    • anti stereochemistry
    • halonium ion
    • back side
    • anti stereochemistry of addition
  8. Halogen addition is another example of a __, in which different stereoisomers of the starting material give different stereoisomers of the product
    stereospecific reaction
  9. A __ is an alcohol with a halogen on the adjacent carbon atom. In the presence of water, halogens add to alkenes to form __. The electrophilic halogen adds to the alkene to give a __, which is also electrophilic. Water acts as a nucleophile to open the __ and form the __.
    • halohydrin
    • halohydrins
    • halonium ion
    • halonium ion
    • halohydrin
  10. Formation of halohydrins
    • 1) electrophilic attack forms a halonium ion
    • 2) water opens the halonium ion; deprotonation gives the halohydrin
  11. When __takes place with no solvent or with an inert solvent such as CCl4 or CHCl3, only the halide ion is available as a nucleophile to attack the __. A __ results.
    • halogenation 
    • halonium ion
    • dihalide
  12. But when an alkene reacts with a haogen in the presence of a nucleophilic solvent such as water, a slovent molecule is the most likely nucleophile ot attack the __. When a water molecule attacks the __, the final product is a __, with a halogen on one carbon atom and a __ on the adjacent carbon. The product may be a __, __, or an __, depending on the halogen.
    • halonium ion
    • halonium ion
    • halohydrin
    • hydroxyl
    • chlorohydrin
    • bromohydrin
    • iodohydrin
  13. Stereochemistry of Halohydrin Formation

    -because the mechanism involves a halonium ion, the __ of addition is __, as in __.
    • stereochemistry
    • anti
    • halogenation
  14. Orientaton of Halohydrin Formation
    - even though a __ is invovled, rather than a carbocation, the extended version of __ applies to __. When propene reacts with chlorine water, the major product has the electrophile chlorine atom) bonded to the __ of the double bond. The mucleophile is bonded to the __.
    • halonium ion
    • Mark's rule
    • halohydrin formation
    • less subbed carbon atom
    • more subbed carbon
  15. The __ observed in halohydrin formation is explained by the structure of the __. The two carbon atoms bonded to the halogen have__, with a __ on the more subbed carbon atom. The nucleophile attacks this more subbed, more electrophilic carbon atom. The result is both __ and __.
    • Markovnikov orientation
    • halonium ion intermediate
    • partial positive charges
    • larger charge
    • anti stereochem
    • Markovnikov orientation
  16. Hydrogenation of an alkene is formally a __, with H2 adding across the double bond to give an __, the process usually requires a catalyst containing Pt, Pd, or Ni.
    • reduction
    • alkane
  17. For most alkenes, __ takes place at room temp, using hydrogen gas at __. The alkene is usually dissolved in an __, an __, or __.
    • hydrogenation
    • atm pressure
    • alcohol
    • alkane
    • acetic acid
  18. A small amount of __, __, or __ is added, and the container is shaken or stirred while the reaction proceeds. Hydrogenation actually takes palce at the surface of the __, where the liquid solution of the alkene comes into contact with __ and the __.
    • platinum
    • palladium
    • nickel
    • metal
    • H
    • catalyst
  19. Hydrogen gas is __ onto the surface of these __, and the catalyst weakens the H-H bond. In fact, if H2 and D2 are mixed in the presence of a platinum catalyst, the two isotopes quickly scramble  to produce a random mixture of HD, H2, and D2. No scarambling occurs in the __.
    • adsorbed
    • metal catalyst
    • absence of the catalyst
  20. Hydrogenation is an example of __, because the (solid) catalyst is in a different phase from the reactant solution. In contrast, __ involves reactants and catalyst in the same phase, as in the acid-catalyzed dehydration of an alcohol.
    • heterogeneous catalysis
    • homogeneous catalysis
  21. Because the two hydrogen atoms add from a solid surface, they add with __ stereochemistry. 

    Soluble homogeneous catalysts, such as __, also catalyze the hydrogenation of C=C
    • syn
    • Wilkinson's catalyst
  22. Wilkinson's catalyst is not __, but its __ can be replaced by __ to give __ that are capable of converting optically inactive starting materials to optically active products. Such a process is called __ or __.
    • chiral
    • triphenylphosphine (PPh3) ligands
    • chiral lligands
    • chiral catalysts
    • asymmetric induction or enantioselective synthesis
  23. __ is particularly important in the pharmaceutical industry because only one enantiomer of a chiral drug is likely to have the desired effect.
    enantioselective synthesis
  24. The correct enantiomer can be synthesized from an __starting material by __ using a complex of rhodium with a chiral ligand called __. Such an __ is more efficient than making a __, resolving it into __, and discarding the unwanted __.
    • achiral 
    • catalytic hydrogenation
    • DIOP
    • enantioselective synthesis
    • racemic mixture
    • enantiomers
    • enantiomer