Final answer:
Isoleucine can be described using the R,S system, which assigns R or S descriptors to the chiral center of the compound. The R or S descriptor is placed within small brackets at the beginning of the compound's name, separated by a hyphen. The configuration of the chiral center is determined by assigning priority to the groups attached to it and visualizing the molecule from the chiral center's perspective.
Step-by-step explanation:
Isoleucine is an amino acid that has a chiral center, meaning it has four different groups attached to a central carbon atom. The R and S system is used to describe the absolute configuration of the chiral center. In the R,S system, the R or S descriptor is placed in front of the compound's name within small brackets, separated by a hyphen.
For example, the R,S system for isoleucine would be (2S,3S)-isoleucine. The R and S descriptors are determined by assigning priority to the groups attached to the chiral center based on the Cahn-Ingold-Prelog rules.
Once the groups are prioritized, you visualize the molecule from the perspective of the chiral center, with the lowest priority group pointing away from you. If the remaining groups are arranged clockwise, it is R configuration. If the groups are arranged counterclockwise, it is S configuration.