Ephedrine and Pseudoephedrine

by James

in Organic Chemistry 1, Stereochemistry

These molecules make the news quite a bit.

1-pseudoephedrine

Some questions to think about:

  • What’s the (R),(S) designation for the stereocenters of ephedrine and pseudoephedrine, as drawn?
  • What’s best way to describe the relationship between these two compounds? Enantiomers? Diastereomers?
  • Let’s say you removed the hydroxyl groups of ephedrine and pseudoephedrine and replaced them with hydrogen. Would the two compounds be enantiomers, diastereomers, or the same?

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{ 7 comments… read them below or add one }

Sue Borchardt

Hmmm. I’m thinking they’re not enantiomers — my memory is that every stereo center would need to be flipped. My orgo skills are rusty but my guess is (R,R) for ephedrine and (S, R) or pseudoephedrine (but I can remember where i’d start numbering carbons so maybe that’s flipped).

I say they’re disasteriomers and they’d be the same compound if you replaced the hydroxyl groups with hydrogen.

Reply

James

right on all counts! [EDIT] – Whoops. actually ephedrine is (S,R) and pseudoephedrine is (S,S). They are diastereomers though.

especially the last one… meth makers are equally happy to obtain ephedrine or psuedoephedrine, since removal of the oxygen converts either one to methamphetamine.

Reply

Ryan

Incorrect. The configurations are suppose to be flipped. But they are diasteromers. http://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/sterism3.htm

Reply

bob

not incorrect…. they are diastereomers…but there is no flipping of anything…as james said, you end up with the same molecule when the hydroxyls are replaced by hydrogen.

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Karin

I get just as Ryan, R,S for Ephedrine and S,S for pseudoephedrine.

Can you explain me what is wrong in my way of thinking? My reasoning is the following Ephedrine is 2-(methylamino)-1-phenylpropan-1-ol and the first carbon is 1R because the priority is 1) -OH; 2) -CNR; 3) -phenyl and the second carbon is 2S because the priority is 1) -NR; 2) -CHOHC6H5; 3) -CH3.

Reply

James Ashenhurst

That is correct. I don’t know how that got messed up. My apologies.

Chris

Perhaps this is a dumb question. But after looking at those two molecules, they look EXACTLY the same. Except that one OH is angled differently that the other. Will there be any difference in molecular properties because of this?

Reply

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