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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Monium101 on July 06, 2014, 08:24:35 PM

Title: Stereochemistry
Post by: Monium101 on July 06, 2014, 08:24:35 PM

I'm having a rather difficult time grasping the concept of drawing pairs of entantiomers and pairs of disastereromers, so example how would I go about drawing these components for an amino acid such as leucine. I know first we can draw the diagram firsthand and label each wedge with the atoms and then we label them from 1-4  typically one has the highest priority since the atom there would have a greater atomic number and then go from there but after this point, everything else is a bit confusing. Can someone break it down for me in terms of labeling the structures first and arranging them please? Thanks in advance! :)

Title: Re: Stereochemistry
Post by: discodermolide on July 06, 2014, 08:33:31 PM

Look up the definition of enantiomers and diastereoisomers.
Then search for the Cahn-Ingold-Prelog system of assigning (R) and (S) to the chiral carbon atoms.
From your question I think this is what you are  getting at.

Title: Re: Stereochemistry
Post by: Monium101 on July 06, 2014, 08:48:46 PM

okay, once I have assigned R and S configurations on the chiral atoms how would I interpret the fact that diastereroisomers are basically stereoisomers that are not entantiomers into drawing them, im still a bit confused.

Title: Re: Stereochemistry
Post by: discodermolide on July 07, 2014, 12:08:21 AM

You use the same method:

where the undefined C-OH is a mixture of enantiomers. This compound is a diastereoisomer.
So the two chiral diastereoisomers are:

and


Note here the Smiles engine has labelled the molecules chiral and are not quite the same as I drew them. But it is correct.