(Electronic) Circular dichroism

• Reaxys property search code: CDIC exists
• The electronic excitation (UV/Visible) spectrum recorded with polarised light
  • 1960s - onwards. The unequal absorption of left and right polarised light
  • The Cotton effect (Compt. Rend. 1895, 120, 989, 1044).
• The ECD spectra (and Cotton effects) of two enantiomers are mirror images.
  • The sign of the Cotton effect defines the absolute configuration
• In recent times, ECD has supplanted ORD ...
  • It can be more sensitive
  • Easier to interpret (ORD subject to "background effects")
    • (somewhat) easier to associate with local structures/stereogenic centres
• But not foolproof (as we will shortly see!).