Enantiomers and geometric isomers

[kfsa1]

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Hi,

I know that enantiomers are by definition non-superimposable images. My question is, how does this apply to geometric isomers? Would E and Z be enantiomers? What about in a compound with a stereocenter R and E - would the enantiomer be S and Z? Also, would a compound with a R and E stereocenter be considered a diastereomer?

Thanks guys,

 

[loveoforganic]

Non-superimposable mirror images - missing one part of the definition, and that should clear up your question. These are only possible about a chiral center and certain cases of steric hinderance

 

[PiBond]

Hi,

I know that enantiomers are by definition non-superimposable images. My question is, how does this apply to geometric isomers? Would E and Z be enantiomers? What about in a compound with a stereocenter R and E - would the enantiomer be S and Z? Also, would a compound with a R and E stereocenter be considered a diastereomer?

Thanks guys,

Geometric isomers are different from enantiomers. E and Z are considered geometric isomers given that the two highest priority groups differ across a double bond, yet their connectivity (bonds) is the same. Enantiomers must have chiral centers that are of opposite configuration at each site, while geometric isomers don't necessarily need chiral centers.

A compound with an R stereocenter and E configuration is not the enantiomer of a compound with an S stereocenter and Z configuration because they're not mirror images even though the absolute configuration at the one chiral center is flipped. They would simply be configurational isomers.

Remember, to have diastereomers we must have a compound with more than one chiral center (minimum of 2). Therefore, the answer to your last question is "no"