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Racemic mixture effect on light

  1. Sep 14, 2014 #1
    Given a racemic mixture with both isomers being optically active, why is it that light can still pass through? If I am not mistaken (this may be completely wrong): the two isomers of a compound, when optically active, polarize light in a plane perpendicular the other. (If this is wrong, please tell me, since that will clear a lot of confusion.)

    Given the above statement, if lights was propagated through two different molecules that polarize light in perpendicular planes, wouldn't there be no resultant light exiting the medium?
  2. jcsd
  3. Sep 14, 2014 #2
    Do all Bronsted-Lowry Acid/Bases work w/ Lewis theory?

    Are all Bronsted-Lowry acid/bases considered acids/bases under Lewis' acid-base theory? I believe my professor mentioned this in passing, though I am not certain if that was out of context or not.

    Water is amphiprotic, correct? It is considered as a Bronsted-Lowry acid and base. Isn't it only a Lewis by itself? Am I missing something? Are there any other compounds like this that are not acids or bases according to Lewis' theory, but are according to Bronsted-Lowry's theory?
  4. Sep 15, 2014 #3


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    Staff: Mentor

    Not perpendicular. They slightly rotate the light, but every single molecule by a very tiny angle.
  5. Sep 17, 2014 #4
    Thank you! Is there any way to estimate/determine the angle the light is polarized purely by looking at the structure of the molecule?
  6. Sep 18, 2014 #5


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    Science Advisor

    No, there isn't. You can calculate it using quantum chemistry but not very precisely. It is also not correct to say that a chiral substance is polarizing the light. Rather it rotates the plane of polarization. That's also why a racemic mixture doesn't act like two crossed polarisators.
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