Molecules with the same chemical formula, the same functional groups of the same carbon

Stereoisomers that are not enantiomers. Diastereomers may be chiral or achiral.

(or diastereoisomers): stereoisomeric structures which are not enantiomers (mirror images) of one another. [Often applied to systems which differ only in the configuration at one carbon atom, e.g. meso- and - or -tartaric acids are diastereoisomeric.