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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: kriggy on May 25, 2016, 11:00:02 AM

Title: diastereoisomers
Post by: kriggy on May 25, 2016, 11:00:02 AM

If I have E and Z alkene, can i say that those molecules are diastereiomers?
those two are isomers, with same connections between atoms (=stereisomers) but are not mirror images of each other.
I got into discussion with my friend and she says that its only used for opticaly active molecules which E and Z isomers are not.

Title: Re: diastereoisomers
Post by: Babcock_Hall on May 25, 2016, 11:20:16 AM

I have seen one classification which divides diastereomers into two subclasses, configurational diastereomers (example:  L-threonine and L-allo-threonine) and cis-trans diastereomers.  However, I am not sure whether or not this classification is universal.

Title: Re: diastereoisomers
Post by: clarkstill on May 25, 2016, 12:10:48 PM

According to the IUPAC definition E/Z isomers are diastereomers:

http://goldbook.iupac.org/D01679.html

But in reality, very few people refer to them as such

Title: Re: diastereoisomers
Post by: kriggy on May 25, 2016, 01:00:20 PM

Yes, thats what I thought. Ok I have one more question about stereochemistry, its not about diastereoisomers but I dont see poin in making new topic:
Can anyone explain the quasiracemate method of determining configuration of compound? From what I understand:
I have unknown compound A and both enantiomers of compound B. Then I "mix them together" and measure melting points seeing that
A+(R)B gave me single minimum in melting point vs composition while A+(S)B gave me two minima and one maximum. From that I can see that A+(S)B makes the quasiracemic mixture and therefore have opposite configurations ie. A has configuration R?