Pfeiffer effect

The Pfeiffer effect is an optical phenomenon whereby the presence of an optically active compound influences the optical rotation of a racemic mixture of a second compound.

Racemic mixtures do not rotate plane polarized light, but the equilibrium concentration of the two enantiomers can shift from unity in the presence of a strongly interacting chiral species. Paul Pfeiffer, a student of Alfred Werner and inventor of the salen ligand, reported this phenomenon.^[1] The first example of the effect is credited to Eligio Perucca,^[2] who observed optical rotations in the visible part of the spectrum when crystals of sodium chlorate, which are chiral and colourless, were stained with a racemic dye.^[3] The effect is attributed to the interaction of the optically pure substance with the second coordination sphere of the racemate.

1. ^ Paul Pfeiffer; Kurt Quehl (1932). "Aktivierung von Komplexsalzen in wäßriger Lösung". Chemische Berichte. 65 (4): 560–565. doi:10.1002/cber.19320650410.
2. ^ E. Perucca "New observations and measurements upon optically active crystals (NaClO₃)” Nuovo Cimento 1919, volume 18, pp. 112.
3. ^ Chemical & Engineering News, Vol. 86 No. 33, 18 August 2008, p. 38, Recognizing a Pioneer

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