text: Enantiomers are molecules having one or more chiral centres that are mirror images of each other. Chiral centres are designated R or S. If the 3 groups projecting towards you are arranged clockwise from highest priority to lowest priority, that centre is designated R. If counterclockwise, the centre is S. Priority is based on atomic number: atoms with higher atomic number are higher priority. If two molecules with one or more chiral centres differ in all of those centres, they are enantiomers.