Chiroptical methods for determining absolute configurations

• Two fundamental differences from crystallography:
  • Performed in solution rather than solid state (solvation)
  • Conformationally (dynamically) averaged measurements
• Four main methods:
  1. Optical rotatory power (1,104,737 substances)
  2. Optical rotatory dispersion (17,555)
  3. Electronic circular dichroism (63,231)
  4. Vibrational circular dichroism (?, low)
     • Vibrational (Raman) optical activity (?, low, mostly biological)

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  What proportion are correlated with absolute configurations?

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• How to interpret the CO spectrum?
  • Is asymmetry/disymmetry global or local?
  • Chromophore is not easily subjected to additive rules!
  • Chromophore varies in its delocalisation (global vs local)