What are the R/S designations of the two stereocenters of L-threonine?

Question

Quizplus · Accepted Answer

L-threonine has two stereocenters, one at carbon 2 and another at carbon 3. To assign R/S designations, we need to prioritize the substituents attached to these carbons based on their atomic number. The priority of substituents attached to carbon 2 is O>C>H, and that of substituents attached to carbon 3 is COOH>OH>H. By comparing the orientation of lowest priority group (H) with the remaining substituents, we find that the configuration at carbon 2 is S and that at carbon 3 is R. Therefore, the R/S designations for L-threonine are 2S,3R. The best choice is option C, which matches this configuration.

What Are the R/S Designations of the Two Stereocenters of L-Threonine