Optical isomerism

• Optical isomerism

  A form of stereoisomerism where atoms/groups are arranged differently around a chiral carbon
• Chiral carbon

  Has 4 different groups attached to it
• Racemic

  A mixture containing equal amounts of each enantiomer
• A racemic mixture is optically inactive because the rotations cancel
• Stereospecific

  A reaction which will only work with one stereoisomer because of the involvement of an active site
• Isomers of chiral compounds are known as enantiomers
• A racemic mixture is often used in dry manufacture because it's difficult and expensive to separate the two isomers
• Optical isomers react acidified hydrogen cyanide

  They form a racemic mixture and the mechanism involved is nucleophilic addition e.g. Ethanal reacting with HCN

  • The CN has a negative charge and a pair of electrons that goes to the carbon with the double bonded oxygen
  • One bond from the double bonded oxygen goes to the oxygen to make it negative
  • The pair of electrons from oxygen goes to the hydrogen
  • And it forms 2-hydroxypropanitile
• How to distinguish between a racemic mixture Vs one of the enantiomers

  You would use plane polarised light, the single enantiomer would rotate light but a racemic wouldn't rotate light
• Give a meaning for the term racemic mixture

  A equal amount of each enantiomers