Orgo 5.14-5.16

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Orgo 5.14-5.16
2013-10-19 18:32:52
CHM 201

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  1. The detailed stereochemical picture of a molecule, including how the atoms are arranged in space. Alternateively, the (R) or (S) configuration at each chirality center
    absolute configuration
  2. Absolute configs were determined through __
    Before that, it was possible to correlate the configuration of one compound with another and to show that two compounds had the same or opposite configurations. When we convert one compound into another using a reaction that does not break bonds at the asymmetric carbon atom, we know that the product must have the same __ as the reactant, even if we cannot determine the absolute configuration of either compound.
    • X-ray crys.
    • relative configuration
  3. __: The experimentally determined relationship between the conigurations of two molecules, even though we may not know the absolute configuration of either.
    Relative configuration
  4. The D-L system is also called the __.
    Fischer-Rosanoff convention
  5. What is the absolute configurations of the glyceraldehyde enantiomers
    • the + enantiomer has the R config, with the -OH group on the right in the Fischer projection
    • the - enantiomer has the S config, with the hydroxyl group on the left
  6. Explain physical properties of enantiomers and diasteromers.
    • enantiomers have identical physical properties except for the direction in which they rotate polarized light
    • diasteromers generally have different physical properties
  7. Diastereomers that are not geometric isomers also have __.
    different physical properties
  8. Because diastereomers have different physical properties, what can we do?
    separate them by ordinary means such as distillation, recrystallization, and chromatography
  9. __ of optically active compounds are often obtained by isolation from biological sources. Most optically active molecules are found as what?
    • pure enantiomers
    • only one enantiomer in living organisms
  10. When a chiral compound is synthesized from achiral reagents, however, a __ results.
    racemic mixture of enantiomers
  11. If we need one pure enantiomer of butan-2-ol, we must find a way of separating it from the other enantiomer. The separation of enantiomers is called __, and it is a different process from the usual physical separations. A __ is necssary for the resolution of enantiomers; such a chiral compound or apparatus is called a __.
    • resolution
    • chiral probe
    • resolving agent
  12. The traditional method for resolving a racemic mixture into its enantiomers is to do what?
    use an enantiomerically pure natural product that bonds with the compound to be resolved
  13. When the enantiomers of hte racemic compound bond to the pure resolving agent, a pair of __ results. The __ are separateed, then the __ is cleaved from the separated enantiomers.
    • diastereomers x2
    • resolving agent
  14. __ is a powerful method for separating compounds. One type invovles passing a solution through a colum containing particles whose surface tends to __ organic compounds.
    • chromatography
    • adsorb
  15. Compounds that are adsorbed strongly do what?
    spend more time on the stationary particles; they come off the column later than less strongly adsorbed compounds, whcih spend more time in the mobile solvent phase
  16. In some cases, enantiomers may be resolved by what?
    passing the racemic mixture through a column containing particles whose surface is coated with chiral molecules
  17. As the solution passes through the column, the enantiomers do what?

    The solvent flows continually through the column, and the dissolved enantiomers gradually move along, retarded by what?
    • form weak complexes, usually through hydrogen bonding, with the chiral column packing. 
    • the time they spend complexed with the column packing
  18. The special feature of this chromatography is the fact that the enantiomers form )) with the chiral column packing. These diastereomeric complexes have different __. 
    They also have different __ and different __ for complexation.
    • physical properties
    • binding energies
    • equilibrium constants
  19. One of the two enantiomers will spend more time complexed with teh __. The more strongly complexed enantiomer passes through the colum __ and emerges from the column after the __.
    • chiral column packing
    • more slowly
    • faster-moving (more weakly complexed) enantiomer