Optical isomerism

    Cards (11)

    • Optical isomers

      Non-superimposable mirror images
    • For a compound the exhibit optical isomerism it must contain a carbon atom bonded to 4 different groups
    • Chiral carbon

      The asymmetric C atom bonded to 4 different groups
    • What are optical isomers called?
      Enantiomers
      example
    • Enantiomers have the same chemical properties as they have the same functional group
      But they differ in their effect on plane polarised light
    • Effect on plane polarised light
      Optical isomers rotate plane polarised light
      by an equal amount
      but in opposite directions
    • To determine if a compound exhibits optical isomerism
      • draw out the structure
      • label the chiral centre with an asterisk *
      • draw out the chiral carbon showing a tetrahedral arrangement of the 4 groups
      • then draw the mirror image of the first structure you have drawn
    • Tips
      Place largest groups above
      make sure bond is always to carbon
    • Racemic
      A mixture of equal amounts of the two enatiomers
      a racemic mixture will not rotate plane polarised light - not optically active
    • Forming enatiomers in the reaction of but-2-ene with Hbr

      Mechanism : electrophilic addition
    • How does the shape of the intermediate lead to mixture with equal amounts of two enatiomers being formed?
      Carbocation is Trigonal planar-not chiral
      Br- ion is equally likely to attack from above or below the plane
      so a racemic mixture is formed and product is not optically active