Question

What does diastereomer mean?

Answer 1

Diastereomers are geometric isomers (typically a pair) that are not mirror images.

Explanation:

Cis and trans isomerism are clearly geometric isomers because they have the same connectivity, but are not mirror images. To resort to the well-worn example of `"2-butylene"`, in BOTH cis and trans isomers, `C1` connects to `C2`......connects to `C4`. Nevertheless, their geometry is clearly distinguishable. For organic molecules that have 2 chiral centres, there are 2 pairs of enantiomers, `R,R` and `S, S`, and `R,S`, and `S,R`. Sometimes, `S, R` is equivalent to `R, S`. Nevertheless `R,S` shares a diastereomeric relationship with `R,R` and `S,S`, the enantiomers.