How the fuke is this a diastereomer?

[Thoroughbred_Med]

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Kaplan Home Review Organic Chemistry Ch. 2 Discrete Practice Questions:

9. Consider (E)-2-butene and (Z)-2-butene. This is a pair of what type(s) of isomers?

I. Cis-trans isomers
II. Diastereomers
III. Enantiomers

A. I only
B. II only
C. I and II only
D. I and III only



The answer is C. Obvi E and Z 2-butene are cis-trans isomers but how in the poop are they diastereomers? I thought diasteromers, by definition, had to have two different chiral centers. There are no chiral centers in 2-butene.

HALP. thx

 

[JoeCaputo]

Cis-trans (E/Z) isomers are diastereomers. Test makers love to catch people using that definition you have. Where did you get it?

 

[Thoroughbred_Med]

Cis-trans (E/Z) isomers are diastereomers. Test makers love to catch people using that definition you have. Where did you get it?

My organic chemistry professor... lol however, Kaplan agrees with you. Diastereomers are, by their definition, molecules that are non-mirror image stereoisomers (stereoisomers being molecules with the same molecular formula and the same connectivity). Further, they are occur when a molecule has two or more stereogenic centers and differs at some, but not all, of these centers. And the cis-trans isomers are a subtype of diastereomers in which the position of substituents differs about an immovable bond.

So I get that the E/Z isomers are stereoisomers... and i get that that they have different substituents that move about an immovable bond. But I DON'T get how where the stereocenters are! There is a not a chiral center in (E) or (Z) 2-butene!

 

[JoeCaputo]

Geometric isomers not stereoisomers

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[Thoroughbred_Med]

bruh your answer can't help me if you don't elaborate

 

[Thoroughbred_Med]

and no, geometric isomerism is a form of stereoisomerism. http://chemwiki.ucdavis.edu/Organic...unds/Geometric_Isomerism_in_Organic_Molecules
1st paragraph chief.

Geometric isomers not stereoisomers

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[JoeCaputo]

bruh your answer can't help me if you don't elaborate

It looks like you have it down now. Good luck.