13.2 Stereoisomerism

• isomer - molecules with the same molecular formula but different structural formula
• stereoisomer - molecules with the same structural formula but different arrangements of atoms in 3D space
• E/Z isomerism:

  only occurs in compounds which have

  • a C=C bond
  • 2 different groups attached to each carbon of the C=C bond
• If the groups of higher priority are on the opposite side of the double bond it is an E-isomer
• If the groups of higher priority are on the same side of the double bond it is a Z-isomer
• Cahn-Ingold-Prelog priority rules:

  • If the first 2 atoms attached to a carbon atom in the double bond are the same, then the first point of difference needs to be found
  • (The priority of an atom depends on its atomic number)
• Cis-trans isomerism:

  • must have a C=C bond
  • 2 different groups must be attached to each carbon of the C=C double bond
  • one of the substituent groups attached to each carbon atom of the C=C bond must be the same
• If the same substituent groups are on the opposite side of the double bond it is a trans-isomer
• If the same substituent groups are on the same side of the double bond it is a cis-isomer