Question: what is the correct absolute configuration assignment at each of the indicated stereocenters

title: Absolute configuration
text: An optical isomer can be named by the spatial configuration of its atoms . The D / L system ( named after Latin dexter and laevus , right and left ) , not to be confused with the d - and l - system , see above , does this by relating the molecule to glyceraldehyde . Glyceraldehyde is chiral itself , and its two isomers are labeled D and L ( typically typeset in small caps in published work ) . Certain chemical manipulations can be performed on glyceraldehyde without affecting its configuration , and its historical use for this purpose ( possibly combined with its convenience as one of the smallest commonly used chiral molecules ) has resulted in its use for nomenclature . In this system , compounds are named by analogy to glyceraldehyde , which , in general , produces unambiguous designations , but is easiest to see in the small biomolecules similar to glyceraldehyde . One example is the chiral amino acid alanine , which has two optical isomers , and they are labeled according to which isomer of glyceraldehyde they come from . On the other hand , glycine , the amino acid derived from glyceraldehyde , has no optical activity , as it is not chiral ( achiral ) .