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enantiomer from Kaplan

Discussion in 'DAT Discussions' started by joonkimdds, Dec 27, 2008.

  1. joonkimdds

    joonkimdds Senior Member
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    Kaplan asks
    "which of the following statements is true about the compounds pictured below?"
    [​IMG]
    and the answer was
    "they are enantiomers which rotate plane-polarized light in different directions."


    I thought R,S configuration has nothing to do with direction of rotation of plane-polarized light. How do we know that the direction of rotation will be oppsite?

    I think I read from somewhere that rotation direction can be deteremined only by expriments and temperature and couple other factors change the degree of rotation but this question is so new to me.
     
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  2. doc3232

    7+ Year Member

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    What we don't know: Whether "R" rotates pos or neg AND to what magnitude.
    We do know that the magnitude of R's rotation will be equal to S's and one will be pos and the other neg.
     
  3. Sublimation

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    All you need to kno from this is that a chiral molecule wil have only one enantiomer that will rotate polarized light in the opposite direction.
     
  4. dominican drums

    dominican drums Excited Pre-Dental Studnt

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    Don't fret. If you can identify these two as enantiomers, you are set. The fact that the answer includes some information about the magnitude of polarization doesn't matter. What does matter is that you recognize that enantiomers can do this, that is, rotate plane polarized light.

    Also, be sure to go over disteromers, meso compounds, and achiral compounds.


    Good Luck
     
  5. joonkimdds

    joonkimdds Senior Member
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    Very interesting info~ none of the books I have stated it as clearly as you did.
    All of them said "R/S has nothing to do with +/-, do not relate them together" so I started to think that they are totally unrelated to each other to make it easier for me to understand.

    Thank u so much everyone.
     
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