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.
do not optical rotation, 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. The first example of the effect is credited to Eligio Perucca,[E. Perucca "New observations and measurements upon optically active crystals (NaClO3)” Nuovo Cimento 1919, volume 18, pp. 112.] 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 mixture dye.[Chemical & Engineering News, Vol. 86 No. 33, 18 August 2008, p. 38, Recognizing a Pioneer] The effect is attributed to the interaction of the optically pure substance with the second coordination sphere of the racemate.