- [L. rectus right] a stereodescriptor used to specify the absolute configuration of compounds having asymmetric carbon atoms. The four different substituents at the asymmetric carbon atom are ranked according to the Cahn-Ingold-Prelog sequence rules; then, looking at the molecule with the lowest ranking substituent pointing directly away from the viewer, if the other three substituents are in clockwise order going from highest to lowest ranked, the configuration is R; otherwise S>. Example: L-threonine is (2S:3R)-2-amino-3-hydroxybutanoic acid.
Medical dictionary. 2011.