Question: what is the difference between stereoisomers and diastereomers?
Answer: Stereoisomers that differ at some stereocenters but not at others are not mirror images, so they are not enantiomers. Instead, they are diastereomers. A diastereomer is simply any stereoisomer that is not an enantiomer. ... Any given molecule has its enantiomer; the two other molecules are its diastereomers.