Question

How many diastereomers can be in any given molecule?

Answer 1

Hint: To determine the answer of this question one should know what is diastereomer, optical isomerism, enantiomers. The maximum number of optical isomers can be where n represents the chiral center.

Complete step by step answer:
Diastereomers are defined as the compounds which contain the same molecular formula and sequence of bonded electrons but they are non-superimposable mirror images. The stereoisomers which contain two or more stereocenters can be considered as diastereomers.
Optical isomerism is the class of isomerism where the compounds have the same molecular formula and same structural formula but cannot be superimposed on each other.
The maximum number of optical isomers can be $2^n$ where n is the number of chiral centres.
The number of diastereomers is less than $2^n$ as the two of the isomers must be a pair of enantiomer.
Enantiomers are considered as the chiral molecules that are mirror images of each other. As, we can say that every other optical isomer is a diastereomer of each enantiomer. Therefore, the maximum number of diastereomers in a molecule is $2^n-2$.

Additional Information:
The difference between the diastereomers and the enantiomers is that enantiomers are mirror images of each other but the diastereomers are not mirror-image of each other but both diastereomers and enantiomers are non-superimposable.

Note: The number of optical isomers decreases if some of the optical isomers are meso compounds. The meso compounds are considered as achiral compounds even though they contain multiple chiral centres. They are optically inactive and are superimposed on its mirror image. Enantiomers and diastereomers are commonly known as stereoisomers.