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

Question

Quizplus · Accepted Answer

L-threonine has one stereocenter at carbon 2 and one stereocenter at carbon 3. The hydroxyl group at carbon 2 is on the left side (counterclockwise direction) and the side chain at carbon 3 is also on the left side. According to Cahn-Ingold-Prelog priority rules, this means that carbon 2 has an S configuration and carbon 3 has an R configuration. Therefore, the R/S designations of the two stereocenters of L-threonine are 2S,3R.

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