Diastereomerism

same but the OH side chain shifts. When you add position isomerism to chain isomerism, you can get a lot of isomers.

There is also functional group isomerism. This involves changing the functional group on the molecule. An example is C3H6O, which could be a ketone (propanone) or an aldehyde (propanal). These are completely different molecules that can be shown in figure 30:

Figure 30.

It is also possible to have an alkene and an alcohol group making up the same molecule in a linear fashion to make CH2CHCH2OH.

DIASTEREOMERISM

The phrase diastereomers can also be referred to as diastereoisomers. These are isomers that are structurally the same but with different appearances that are not considered mirror images. When they differ at one stereocenter, they are referred to as “epimers”. D-threose and D-erythrose are structurally the same but look different from a molecular standpoint. As you can see in figure 31, they are not mirror images.