Nomenclature

Natural and unnatural amino acids and sugars were the first molecules to be defined as chiral and the terms D (dextro) and L (laevo) were associated with the isomers. Each isomer was called an enantiomer and the unseparated mixture, which comprised equal numbers of molecules of each enantiomer, was termed racemic or a racemate. Amino acids and sugars are still named in this way but R & S nomenclature is now more commonly used for other molecules.

In a typical situation with chirality as a C atom it is necessary to prioritise the atoms. The atoms with the highest atomic number in the periodic table gets priority No one. Arrange the molecules so that the atom with the lowest priority is facing away from you (often this is a hydrogen atom). If they go clockwise from 1-3 then the molecule is R. If they go anti-clockwise then it is S.