Question

How would you find the number of diastereomers?

Answer 1

Total number of possible stereomers `=2^n` where `n=` number of chiral centers.

To find diastereomers, you must look at Fischer projections to find nonsuperimposable, non-mirror-image molecules.

Explanation:

The maximum number of stereomers possible for a compound is equal to `2^n` where `n` is the number of asymmetrical carbons (chiral centers) in a molecule.

To find the number of diastereomers, you would have to draw different stereomers in Fischer projections. Don't forget that enantiomers and meso compounds are considered stereomers but not diastereomers. Diastereomers are compounds that have the same molecular formula and are nonsuperimposable but are not mirror images of one another.

Consider 2,3-dibromobutane

The top two Fischer projections show meso-compounds that have an internal plane of symmetry and are the same compound. The bottom two are enantiomers. The top-left compound (2R,3S) and the bottom-left compound (2R,3R) are nonsuperimposable and are not mirror images of one another. They are diastereomers. The same can be said for the top-right (2S,3R) and the bottom-right (2S,3S). 2,3-dibromobutane has a total of 3 stereomers.