R and S nomenclature system was given by Cahn, Ingold, and Prelog. This nomenclature tells the configuration of the chiral center. In a pair of enantiomers having a chiral center one out of two will have R configuration and the other will have S configuration. If the sequence of groups attached to the chiral center is left to right then it is R configuration and if the sequence is from right to left then it is S configuration.This system is based on the 3-Dimensional formula and not on the 2 -D Projection. The priority of the groups attached to the chiral carbon is determined by various priority sequence rules.