Question

How do diastereomers differ from optical isomers?

Answer 1

Stereoisomers is the class of isomers under which enantiomers and diastereomers are present. Diastereomers are the compounds which are not mirror images of each other and are non-superimposable. The enantiomers are the mirror image of each other and are non-superimposable.

Complete step by step answer:
When two molecules are stereoisomers which means they possess the same molecular formula, same connectivity but different arrangement of atoms but are not enantiomers then they are considered as diastereomers.
The diastereomers have different physical properties like melting points, boiling point, solubilities. Diastereomers other than geometrical isomers may or may not be optically active. Diastereomers show similar but not identical chemical properties.
Optical isomers are two compounds which contain the same number and kinds of atoms, and bonds but differ in the arrangement of the atoms but are non-superimposable mirror images of each other. Each non-superimposable mirror image structure is called an enantiomer. Molecules or ions that are present in optical isomers are called chiral.
The optical isomers are optically active as they rotate the plane of plane polarized light which is passed through the sample of enantiomers.
Difference can be given in table form as shown below.

Diastereomers	Optical isomers
Diastereomers come under the class of isomers known as stereoisomers.	Optical isomers come under optical isomerism.
contain one or more chiral center	Contain optical center
May or may not be optically active	They are optically active
They are not enantiomers	Optical isomers are enantiomers
Superimposable mirror image	Non-superimposable mirror image

Note:
It is not compulsory for a compound to be optically active if it contains a chiral center. Diastereomers contain two or chiral centers but are not able to rotate the plane polarized light as they are superimposable on each other.