Stereochemistry of Amino Acids: Optical Properties

All  amino acids (except glycine) rotate the plane of polarized light because of  the presence of an asymmetric center at C-2. Both L and D enantiomers are possible for the  amino acids. What  do we mean  by  enantiomers? Do you  recall reading about them  in  the last unit  under the topic of isomerism? Like carbohydrates, amino acids too exist as L and D  isomers. The definition of D and L depends on  the position of -NH2  group on C-2. When  the amino group is on the left of C2, it  is called L  form. Essentially, all the amino acids  in  the diet and  in the body occur as the L isomer as shown in Figure