3.7 Optical Isomers

• What is stereoisomerism?


  same molecular formula but different arrangement of atoms in a 3D space
• What are optical isomers?

  Enantiomers which is non-superimposable and contains a chiral carbon
• What is a chiral carbon?

  Carbon atom with four different groups attached
• What shape do optical isomers form?

  Tetrahedral (109.5)
• What is plane polarised light?

  Only light oscillating in one plane can pass through
• What will optically active molecules do to plane polarised light?

  Rotate plane polarised light
• Why do optically active molecules rotate plane polarised light?

  Contain a chiral carbon
• What are racemic mixtures (racemates)?

  Two enantiomers that will rotate plane polarised light equally but in different directions.
• How can you distinguish between the two enantiomers in a racemic mixture?

  The difference in physical properties
• When will chiral molecules show optical activity?


  If one isomer is present in greater quantities
• What will be produced in an addition reaction and why?

  Racemate - attacking Nucleophilic or electrophile can attack the planar molecule from above or below with equal probability
• What will be produced in a substitution reaction and why?

  Single enantiomer - attacking species can only attack from one side as long as the reacting chiral molecule was also a single enantiomer
• Why is only one optical isomer used in drug action?

  Different optical isomers may have very different biochemical effects e.g one isomer may be effective the other is toxic