Ultraviolet–visible spectroscopy (UV–vis) can distinguish between

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

s by showing a distinct

Cotton effect The Cotton effect in physics, is the characteristic change in optical rotatory dispersion and/or circular dichroism in the vicinity of an absorption band of a substance. In a wavelength region where the light is absorbed, the absolute magnitude o ...

for each isomer. UV–vis spectroscopy sees only

chromophore A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...

s, so other molecules must be prepared for analysis by chemical addition of a chromophore such as anthracene. Two methods are reported: the octant rule and the exciton chirality method. The octant rule was introduced in 1961 by William Moffitt,

R. B. Woodward Robert Burns Woodward (April 10, 1917 – July 8, 1979) was an American organic chemist. He is considered by many to be the most preeminent synthetic organic chemist of the twentieth century, having made many key contributions to the subject, ...

, A. Moscowitz,

William Klyne William Klyne (March 23, 1913, in Enfield, Middlesex – November 13, 1977) was an organic chemist known for his work in steroids and stereochemistry — a field in which he was a "pioneer", and in which Ernest Eliel and Norman Allinger Nor ...

and

Carl Djerassi Carl Djerassi (October 29, 1923 – January 30, 2015) was an Austrian-born Bulgarian-American pharmaceutical chemist, novelist, playwright and co-founder of Djerassi Resident Artists Program with Diane Middlebrook, Diane Wood Middlebrook. He is b ...

.''A Simple Computer-Aided Three-Dimensional Molecular Modeling for the Octant Rule'' Yinan Kang , Fu-An Kang J. Chem. Educ., 2011, 88 (4), p 420 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 of an enantiomer.

References

{{DEFAULTSORT:Ultraviolet-visible spectroscopy of stereoisomers Spectroscopy

See also

References