Optical Isomerism

• Structural isomers are compounds with the same molecular formula but a different structural formula
• Match the type of structural isomerism with its description:

  Functional group ↔️ Compounds with different functional groups

  Position ↔️ Compounds with different positions of the same group

  Chain ↔️ Compounds with different carbon chain arrangements
• Stereoisomers have the same structural formula but a different arrangement of atoms in space.
• E/Z isomerism occurs due to restricted rotation about a carbon-carbon double bond
• Steps to determine if an alkene is the E or Z isomer

  1️⃣ Identify the highest priority group on each carbon atom of the C=C bond

  2️⃣ If both highest priority groups are on the same side, it is the Z isomer

  3️⃣ If both highest priority groups are on opposite sides, it is the E isomer
• The Cahn-Ingold-Prelog (CIP) priority rules state that the atom with the highest atomic number has the highest priority
• Optical isomers are non-superimposable mirror images.
• What is the term for a carbon atom bonded to four different groups?

  Chiral carbon
• Optical isomers rotate plane polarised light by an equal amount but in opposite directions
• Steps to identify and draw optical isomers

  1️⃣ Draw the structure of the compound

  2️⃣ Label the chiral centre with an asterisk (*)

  3️⃣ Draw the chiral carbon with a tetrahedral arrangement of groups

  4️⃣ Draw the mirror image of the structure
• A racemic mixture does not rotate plane polarised light
• Why does the carbocation in the reaction of but-2-ene with HBr lead to a racemic mixture?

  It is trigonal planar
• The Br⁻ ion in the reaction of but-2-ene with HBr is equally likely to attack from above or below the plane.