Again, make sure that you see the different isomer represented by each diagram. This last example has produced an example of stereoisomers which are not enantiomers. Remember that enantiomers are mirror images of each other, and so there are only ever two. If there are two or more chirality centres, then to obtain the enantiomer of a molecule, two groups must be interchanged at each chirality centre as reflection in a mirror will invert everything in the molecule. Diastereoisomers are stereoisomers which are not enantiomers.
Exercises Try the following exercises .