13.2 Stereoisomerism

• Stereoisomers have the same structural formula but a different arrangement of the atoms in space
• The pi bond restricts rotation about the double carbon-carbon bond, which results in the groups attached to each carbon to be in a fixed position
• A molecule has E/Z isomers if

  • there is a carbon-carbon double bond
  • there are two different groups attached to the carbons
• CIP rules are used to classify E and Z alkenes

  • atom with the greater atomic number are given priority
  • Z isomers have priority on the same side
  • E isomers have priority on different sides
• Cis-trans isomers are special cases of E/Z isomers in which one of the groups attached to both carbons are the same

  • Cis isomers have them on the same side
  • Trans isomers have them on different sides
• If the first atom has the same priority, you continue along the chain until you find atoms with different atomic numbers