Chirality and optical isomerism

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  • Created by: Anon
  • Created on: 10-03-15 15:13
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  • Chirality and optical isomerism
    • Optical isomerism
      • Optical isomerism occurs if a molecule has a chiral centre
        • A chiral centre had 4 different groups/ atoms attached to the same atom
        • Optical isomers are non-superimposable mirror images
        • Chiral centres are often represented by *
      • Optical isomerism is a type of stereoisomerism
        • The isomers have the same structural formula, but a different arrangement in space
        • Another type of isomerism is E/Z
        • For E/Z isomerism you need a C=C, because a double bond lacks rotation
        • An E/Z isomer must also have at least 2 different groups on each carbon atom
      • When representing optical isomers in the exam, they should be mirror images of each other
    • Optical isomerism in phamaceutica-ls
      • Drugs are usually reasonably large molecules, so it follows that the chance of them having a chiral centre is high, which can cause problems
      • Problems of optical isomerism
        • One isomer may be biologically inactive and so a double dose is needed
        • One isomer may have harmful side effects
        • Optical isomers are very, very expensive to separate
      • Solutions for optical isomerism
        • Chiral pool synthesis. Meaning you have an optically pure starting material
        • A naturally occuring enzyme could be used to synthesise the drug (if there is one)
        • As a last resort you could separate the isomers by chromatography
          • But this is very expensive
          • It is quite difficult to separate isomers that are so chemically similar
  • Solutions for optical isomerism
    • Chiral pool synthesis. Meaning you have an optically pure starting material
    • A naturally occuring enzyme could be used to synthesise the drug (if there is one)
    • As a last resort you could separate the isomers by chromatography
      • But this is very expensive
      • It is quite difficult to separate isomers that are so chemically similar

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