`D` configuration: (a) (`-OH` on `C_3` is on the right).
`L` configuration : (b) (convert to Fischer, `-NH_(2)` is on the left (c ) (`-OH` on `C-3` is on the left side.)
i. Erythro and threo designation: Compounds with two adjacent chiral (stereogenic) `C` atoms are sometimes designated by prefix 'erytho or thero' (Name of two `C-2` epimeric aldoteroses.
These prefixes are used to distinguish between enantiomers containing two chiral `C` atom when two pairs of substituents attached ot each chiral `C` are the same while the third is different, e.g., system of the type
`[R-C(x)(y)-C(x)(y)-R']` and `[R-C(x)(y)-C(x)(z)-R']`.
The stereoisomers in which the same group are present on the same side of the Fischer projection are called erythro isomers while the stereoisomers in which these goups are present on the opposite sides are known as threo isomers.
