Question

If the two stereogenic centers of a compound are R,S in configuration, what are the R,S assignments for its enantiomer and two diastereomers?

Short answer

R, R for enantiomers.

R, R and S, S for diastereomers.

Step-by-step solution

Enantiomers  

The enantiomers contain chiral centers (with four different groups), and they are identified by the inverted stereochemistry.

For example, the R isomer, and S isomer are enantiomers.

Diastereomers

The diastereomers also contain chiral centers or stereogenic centers, and they are identified by the difference in stereochemistry at only one center.

For example, the R, S isomer and R, R isomer are diastereomers.

Explanation

1. The R, S assigned molecule has its enantiomer with S, R stereochemistry. The stereochemistry is inverted in this case due to non-superimposable mirror images.
2. The R, S assigned molecule has its diastereomer with S, S stereochemistry. The stereochemistry of one chiral atom remains the same in this case due to not having any mirror image relationship.