How do you identify diastereomers?

1 Answer
anor277
Jan 16, 2017

Diastereomers are geometric isomers that are NOT mirror images.

Explanation:

Given a pair of geometric isomers, WE KNOW that they have the same connectivity. What do I mean by this?

If we take #"trans-2-butene"# versus #"cis-2-butene"#, clearly the connectivity of each isomer are the same, i.e. #C1# connects to #C2# connects to #C3# connects to #C4#. Yet, nevertheless the trans isomer is manifestly different geometrically to the cis isomer. #"Trans-2-butene"# and #"cis-2-butene"# are #"geometric isomers"# with different physical and chemical properties.

See this old answer for examples where the geometric isomers are distinguished by their handedness. For the olefins, GENERALLY, the cis isomer is MORE volatile, tho I think for this example the trans isomer has the lower boiling point.

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