What are Diastereomers?
We said “enantiomers are molecules in which all stereogenic centers are in the opposite configuration (R or S).” So what are diastereomers? Well what happens if you have multiple stereogenic centers and some match, but others don’t? Then, you have diastereomers (or diastereo-isomers).
Say that your molecule has 2 stereogenic centers that are both in the R configuration (R,R). If we change one stereogenic center’s configuration, it could become R,S. When comparing these 2 molecules, we have multiple stereogenic centers (we have 2), and some stereogenic centers match (the 1st letter, R) and others don’t (the 2nd letter, S). This is when we have a diastereomer. The molecule with configuration S,R would also be a diastereomer. But the molecule with the S,S configuration would not be diastereomer because all the stereogenic centers in it are the opposite configuration, which mean we have an enantiomer.
To complete the table given at the beginning of the chapter: