Tuesday, December 4, 2018

stereochemistry - How do we identify left handed and right handed crystals?


I was going through this article about how Louis Pasteur studied and explained the absence of optical activity in Racemic acid. Here's an extract:





When Pasteur next examined crystals of the same salt of racemic acid, he found that they, too, were chiral but that some of the crystals were left-handed and others were right-handed. The crystals were related to one another as an object and its non-superimposable mirror image, and they were present in equal amounts. With a magnifying lens and a pair of tweezers, Pasteur carefully separated these crystals into two piles: the left-handed ones and the right-handed ones.






My guess is that the left/right handedness refers to the molecular spatial alignment. So,

  • How exactly can you assign the property of individual molecules to an entire crystal?

  • How can you determine if a crystal is left/right handed just by looking at it?




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