The a-carbons for 19 of them are asymmetric (or chiral), thus being able to have two enantiomers. Glycine has no chirality RS system re-viSited( Chapter 3, p60) The priorities of some common substituents are OCH2>-OH>-NH2>-C00H>-CHO>-CH2OH>-CH3>-H The chiral atom is viewed with the group of lowest priority pointing away from the viewer. If the priority of the other three groups decreases in clockwise order. the configuration isR(right); if in counterclockwise order, the configuration isL(eft”) CoO COO HRN O 0 NH3 13 CH3 L-Alanine D-Alanine (aThe -carbons for 19 of them are asymmetric (or chiral), thus being able to have two enantiomers. Glycine has no chirality. RS system re-visited (Chapter 3, p60): The priorities of some common substituents are -OCH2 > -OH > -NH2 > -COOH > -CHO > -CH2OH > -CH3 > -H The chiral atom is viewed with the group of lowest priority pointing away from the viewer. If the priority of the other three groups decreases in clockwise order, the configuration is R (“right”); if in counterclockwise order, the configuration is L (“left”)