Regioselective reactions are primarily associated with addition reactions to non-symmetric alkenes, alkynes, and aromatic compounds. By definition, adding a unique functionality on either site (region) of the substrate generates a unique molecule. Regioselective reactions show a preference for one site (region). E.g. electrophilic addition to alkenes or Saytzeff eliminations. Regioselective hydration of 3-methyl-2-heptene at either region Stereoselective reactions are those in which one enantiomer/diastereomer/epimer of possibly two or more is produced predominantly. Stereoselective reactions are enantioselective, diastereoselective, or both. When a single chiral center is produced due to a reaction, the reaction is said to be enantioselective or asymmetric if one of the two enantiomers predominates.