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enantiomers

Ephedrine and Pseudoephedrine

These molecules make the news quite a bit. Some questions to think about: What’s the (R),(S) designation for the stereocenters of ephedrine and pseudoephedrine, as

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A simple trick: The (R)-(S) Toggle

Instead of redrawing the whole molecule, just leave the hydrogen (or other 4th ranked substituent) in front and figure out whether the substituents ranked 1,2, and 3 go clockwise or counterclockwise. Then toggle (i.e. reverse direction CW to CCW or vice versa) to account for the fact that the 4th ranked substituent is in the front, and assign (R) or (S) based on that. You end up with the same answer without having to redraw anything.

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