Optical Rotatory Power, [α]_D

• The rotation of polarised light at 589 nm (the sodium D line).
• Reaxys property search code: ORP exists or ORP.ORP between -200 and +200
• First observed by Biot in 1832
• Made famous by Pasteur in 1848
• and the only structural spectroscopic method routinely available for synthetic chemists up to about 1925!
  • Beckmann, 1889 used it to initiate the concept of reaction mechanism
  • Walden in 1896 used it to infer inversion of configuration in Sn2 reactions
  • Meerwein in 1924 used it to infer carbocations as reactive intermediates
• But thought useless for determination of absolute configurations ..
  • Because the sign/value cannot be reliably predicted from simple additivity rules based on functional groups
    • Example: Lowe's 1965 rule for axially dissymmetric molecules
    • 1981: Violation of Lowe's rule
  • The 589nm chromophores tend to be a global property rather than reflecting upon the stereogenic centres

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  Is there a solution?

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