The Pfeiffer Effect is an optical phenomenon whereby the presence of an optically active compound influences the optical rotation

Optical rotatory dispersion

Optical rotatory dispersion is the variation in the optical rotation of a substance with a change in the wavelength of light. Optical rotatory dispersion can be used to find the absolute configuration of metal complexes....

 of a racemic mixture of a second compound.

Racemic mixtures do not rotate plane polarized light

Optical rotation

Optical rotation is the turning of the plane of linearly polarized light about the direction of motion as the light travels through certain materials. It occurs in solutions of chiral molecules such as sucrose , solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms...

, but the equilibrium concentration of the two enantiomers can shift from unity in the presence of a strongly interacting chiral species. Paul Pfeiffer

Paul Pfeiffer (chemist)

Paul Pfeiffer was an influential German chemist. He received his Ph.D. under Alfred Werner, the "father of coordination chemistry," at the University of Zurich...

, a student of Alfred Werner

Alfred Werner

Alfred Werner was a Swiss chemist who was a student at ETH Zurich and a professor at the University of Zurich. He won the Nobel Prize in Chemistry in 1913 for proposing the octahedral configuration of transition metal complexes. Werner developed the basis for modern coordination chemistry...

 and inventor of the salen ligand

Salen ligand

Salen is the abbreviation for a popular chelating ligand used in coordination chemistry and homogeneous catalysis. The name salen is a contraction for salicylaldehyde and ethylenediamine. The ligand is a bright yellow micaceous solid that is soluble in polar organic solvents.-Nomenclature:The...

, reported this phenomenon. The first example of the effect is credited to Eligio Perucca

Eligio Perucca

Eligio Perucca was an Italian Physics instructor and researcher at the University of Turin in Italy in the early decades of the twentieth century. He later served a professorship at the nearby Polytechnic University of Turin...

, who observed optical rotations in the visible part of the spectrum when crystals of sodium chlorate

Sodium chlorate

Sodium chlorate is a chemical compound with the chemical formula . When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 250 °C to release oxygen and leave sodium chloride...

, which are chiral

Chirality (chemistry)

A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

 and colourless, were stained with a racemic dye.