Racemic mixture effect on light

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Discussion Overview

The discussion centers around the effects of racemic mixtures on light polarization, particularly focusing on the behavior of optically active isomers and their interaction with polarized light. Participants explore concepts related to optical activity, the nature of light rotation by chiral molecules, and the implications of these properties in racemic mixtures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why light can pass through a racemic mixture if both isomers are optically active, suggesting that they polarize light in perpendicular planes.
  • Another participant corrects this notion, stating that the isomers do not polarize light perpendicularly but rather rotate the light slightly by a small angle.
  • A later reply seeks to clarify whether it is possible to estimate the angle of light polarization based solely on the molecular structure.
  • Another participant asserts that while quantum chemistry can be used to calculate the angle, it cannot be done precisely, and emphasizes that chiral substances rotate the plane of polarization rather than polarizing light in a conventional sense.

Areas of Agreement / Disagreement

Participants express disagreement regarding the initial claim about perpendicular polarization of light by isomers. There is no consensus on the ability to estimate the angle of polarization from molecular structure, as responses indicate varying levels of certainty and methods of calculation.

Contextual Notes

Participants acknowledge limitations in estimating polarization angles and the precision of quantum chemistry calculations. The discussion also highlights the distinction between polarizing light and rotating its plane of polarization.

Who May Find This Useful

This discussion may be of interest to those studying optical activity, chiral molecules, and the principles of light interaction with matter, particularly in the context of chemistry and physics.

MathewsMD
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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?
 
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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?
 
MathewsMD said:
the two isomers of a compound, when optically active, polarize light in a plane perpendicular the other

Not perpendicular. They slightly rotate the light, but every single molecule by a very tiny angle.
 
Borek said:
Not perpendicular. They slightly rotate the light, but every single molecule by a very tiny angle.

Thank you! Is there any way to estimate/determine the angle the light is polarized purely by looking at the structure of the molecule?
 
MathewsMD said:
Thank you! Is there any way to estimate/determine the angle the light is polarized purely by looking at the structure of the molecule?

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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