Stereoisomerism

• What are stereoisomers?


  Compounds with the same structural formula but with a different arrangement of the atoms in space
• What two conditions do stereoisomerism require?


  • a C=C double bond

  • different groups attached to each carbon atom of the double bond
• why does but-1-ene not have E/Z isomers despite having a double bond?


  C atom on left side of C=C attached to 2 H atoms

  : not 2 different groups (2nd condition)

  -> won't display E/Z isomerism
• What is cis-trans isomerism?


  Special type of E/Z isomerism where the two substituents on each carbon atom are the same
• In cis-trans isomerism, one of the attached groups on each carbon must be ____


  Hydrogen
• Which isomer is cis isomer?


  Z isomer
• Which isomer is trans isomer?


  E isomer
• In the trans isomer, the hydrogens are what?


  Diagonally opposite each other
• In the cis isomer, the hydrogens are what?


  On the same side of the molecule
• What is Cahn-Ingold-Prelog nomenclature?


  An E-Z system of naming which is used when there are isomeric compounds containing C=C bonds but each carbon atom in the double bond is attached to a single hydrogen atom
• In the Cahn-Ingold-Prelog nomenclature, the atoms attached to each carbon atom in a double bond are given a priority based on what?


  their atomic number
• What's step 1 of Cahn-Ingold-Prelog nomenclature?


  Examine the atoms attached directly to the carbon atoms of the double bond and decide which if the two atoms has the highest priority. The higher the atomic number, the higher the priority
• What's step 2 of Cahn-Ingold-Prelog nomenclature?


  If the two atoms attached to a carbon atom in the double bond are the same, then you will need to find the first point of difference. The group which has the higher atomic number at the first point of difference is given the priority
• Which isomer is this: If the groups of higher priority are on the same side of the double bond?


  Z isomer
• Which isomer is this: If the groups of higher priority are diagonally placed across the double bond?


  E Isomer
• C=C is planar

  Carbon atoms in a C=C double bond and the atoms bonded to these carbons all lie in the same plane (they are planar). Because of the way they're arranged, they're actually said to be trigonal planar.
• Atoms cant rotate around C=C double bonds

  Because of the way the p-orbitals overlap to form a pi bond