Question: Draw the other three stereoisomers of L-isoleucine, and label the stereogenic centers as R or S.

Stereoisomers also have another designated name called spatial isomers. These isomers comprise equivalent molecular formulas but the atoms are positioned differently.

Stereogenic centres possessing R and S configuration are allocated based on the Cahn-Ingold Prelog rules.

On proceeding from higher priority to lower priority, the substituent in the clockwise direction is designated R. The substituent in the anticlockwise direction is designated as S.

L-leucine possesses two stereogenic centres. The maximum number of stereoisomers are calculated using the formula:

$\mathrm{Number}\mathrm{of}\mathrm{stereoisomer}=2^{\mathrm{n}}$

Where n denotes the number of stereogenic centres. So the number of stereoisomers in isoleucine is 4.

The structure of L-isoleucine can be given as:

Structure of L-isoleucine

The other three stereoisomers of L-isoleucine with the labeled stereogenic centres are given as:

Stereoisomers of L-isoleucine

The R or S configuration for first, second and third stereoisomers are (2R,3R), (2R, 3S) and (2S, 3R).