A pair of stereoisomers those are not mirror image to each others are called Diastereomers.
Diastereomerism is observed both in Geometrical as well as in optical isomers.
Diastereomers have different electronic environment hence have different physical and chemical property. They have different dipole moment, melting point , boiling point or solubility, They can be easily seperated by evaporation or fractional distillation .
Diastereomers is a relationship between two stereoisomers. Optical diastereomers have identical but opposite θ value (SPECIFIC ROTATION).
Example 1 : Diastereomeric pair of Dichlorobutane :
Example 2 : Diastereomeric pair of Dichlorocyclopropane:
Example 3 : Trifluoropentane Diastereomers:
Example 4 : Dichlorocyclobutane Diastereomers
Example 5 : Trichlorocyclobutane Diastereomers