Optical isomerism

• Describe the nomenclature of compounds containing more than one functional group

  If one of the functional groups is:

  • An amine or halogenoalkane, the necessary prefix is added e.g. chloro, amino
  • An alcohol and the other is a nitrile or anything containing a C=O bond, the alcohol group is named using a hydroxy- prefix
  • An alcohol and the other is anything other than an amine or a haloalkane, the -an- is replaced with -en-
• What are the two types of isomerism?

  Structural isomerism and stereoisomerism
• What are the three types of structural isomerism?

  Positional isomerism

  Chain isomerism

  Functional isomerism
• What are the two types of stereoisomerism?

  Geometrical isomerism

  Optical isomerism
• Describe optical isomerism

  -All molecules have a mirror image but often that image is the same molecule, but sometimes the mirror image is a different molecule.

  -Molecules have optical isomers if their mirror images are non-superimposable

  -Molecules containing C with 4 different groups attached to it exhibit optical isomerism

  -This C atom is called a chiral carbon atom
• How do you distinguish between optical isomers?


  One physical method:

  • If plane-polarised light is passed through a liquid containing a chiral molecule, the plane of light will be rotated
  • This can be detected using a polarimeter
  • Two optical isomers will rotate plane-polarised light equally, but in opposite directions
  • A substance which can rotate the light is said to be optically active
• Describe the importance of optical isomers in biochemistry

  In drug making, the drugs must be specific to the enzyme they are reacting with. Enzymes are stereospecific which means they only match with one optical isomer
• Define racemates

  Optical isomers are often found together in a mixture in equal quantities. The opposite effect on the rotation of plane-polarised light will result in no overall rotation. An equimolar mixture of two optical isomers will have no effect on plane polarised light and is not optically active
• What is the product if the chiral substance is produced by an addition reaction?

  A racemate

  • The attacking electrophile or nucleophile can attack the planar molecule from above or below with equal probability