The Cahn-Ingold-Prelog convention is the most widely accepted system for naming the configurations of chirality centers. Each asymmetric carbon atom is assigned a letter (R) or (S) based on its three-dimensional configuration. To determine the name, we follow a two-step procedure that assigns "priorities" to the four substituents and then assigns the name based on the relative positions of these substituents. The procedure follows:

• Rank the groups (or atoms) bonded to the asymmetric carbon in order of priority. The atomic numbers of the atoms directly attached to the asymmetric carbon determine the relative priorities. The higher the atomic number, the higher the priority.

Examples of priority for atoms bonded to an asymmetric carbon:

 

• In case of ties, use the next atoms along the chain of each group as tiebreak-ers. For example, we assign a higher priority to isopropyl  -CH(CH₃)₂ than to ethyl -CH₂CH₃ or bromoethyl -CH₂CH₂Br. The first carbon in the isopropyl group is bonded to two carbons, while the first carbon in the ethyl group (or the bromoethyl group) is bonded to only one carbon. An ethyl group and a -CH₂CH₂Br have identical first atoms and second atoms, but the bromine atom in the third position gives -CH₂CH₂Br a higher priority than -CH₂CH₃. One high-priority atom takes priority over any number of lower-priority atoms.