Ultraviolet-visible spectroscopy of stereoisomers
Ultraviolet-visible spectroscopy
Ultraviolet-visible spectroscopy
Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent ranges...

 (UV-vis) can distinguish between enantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

s by showing a distinct Cotton effect
Cotton effect
The Cotton effect is the characteristic change in optical rotatory dispersion and/or circular dichroism in the vicinity of an absorption band of a substance....

 for each isomer. UV-vis spectroscopy sees only chromophore
A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...

s, so other molecules must be prepared for analysis by chemical addition of a chromophore such as anthracene
Anthracene is a solid polycyclic aromatic hydrocarbon consisting of three fused benzene rings. It is a component of coal-tar. Anthracene is used in the production of the red dye alizarin and other dyes...

. Two methods are reported: the octant rule and the exciton chirality method.
The octant rule was introduced in 1961 by William Moffitt
William Moffitt
William E. Moffitt was a British quantum chemist. He died after a heart attack following a squash match. He had been thought to be one of Britain’s most gifted academics.-Early life:...

, R. B. Woodward, A. Moscowitz, W. Klyne and Carl Djerassi
Carl Djerassi
Carl Djerassi is an Austrian-American chemist, novelist, and playwright best known for his contribution to the development of the first oral contraceptive pill . Djerassi is emeritus professor of chemistry at Stanford University.He participated in the invention in 1951, together with Mexican Luis E...

 . This empirical rule allows the prediction of the sign of the Cotton effect by analysing relative orientation of substituents in three dimensions and in this way the absolute configuration
Absolute configuration
An absolute configuration in stereochemistry is the spatial arrangement of the atoms of a chiral molecular entity and its stereochemical description e.g. R or S....

of an enantiomer.
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