Optical Rotatory Dispersion. Circular Dichroism

Optical rotations usually are measured at just one wavelength, namely 589.3 nm, simply because sodium-vapor lamps provide an especially convenient source of monochromatic light. Measurements at other wavelengths are less easily made without specialized instruments, with which relatively few laboratories are currently equipped. Nevertheless, much information has been obtained about structure, conformation, and configuration of organic compounds from measurements of optical rotation as a function of wavelength (i.e., optical rotatory dispersion). 

This means that the molar extinction coefficients of the two enantiomers (e, and er) are unequal in circularly polarized light. These differences in absorption (e, and er) can be measured as a function of wavelength, and the curves obtained are called circular dichroism curves. They have positive or negative signs (Cotton effect) just as for optical rotatory dispersion curves. 

Most of the research on optical rotatory dispersion to date has been with optically active ketones because the carbonyl chromophore conveniently has a weak absorption band in the 300 nm region. Compounds with chromophores that absorb light strongly in the ultraviolet usually are unsatisfactory for rotatory dispersion measurements because insufficient incident light is transmitted to permit measurement of optical rotation. Weak absorption bands below about 210 nm have not been exploited because of experimental difficulties in making the necessary measurements. 

Many rotatory dispersion curves have been obtained for optically active ketones derived from steroids and triterpenes, which are monocyclic, bicyclic, and open-chain compounds. Enough data have been accumulated so that the various shapes and magnitudes of the curves are recognized as characteristic of particular structural features. A good illustration is provided by the rotatory 

Rotatory dispersion curves often are helpful in establishing configurations thus the relative configurations of compounds 18 and 20a must be the same because, if they were not, the two curves would resemble mirror images of one another. Therefore, if the absolute configuration of 18 corresponds to the formula shown, then compound 20a has the configuration shown and not 20b. 

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Electronic Spectra, Optical Rotatory Dispersion-Circular Dichroism... 

Other methods have also been used, including optical rotatory dispersion, circular dichroism (CD), and asymmetric synthesis (see p. 147). 

The inherent difficulty in analyzing enantiomers arises from the well-known fact that apart from their chiroptical characteristics, optical isomers have identical physical and chemical properties in an achiral environment (assuming ideal conditions). Therefore, methods of distinguishing enantiomers must rely on either their chiroptical properties (optical rotation, optical rotatory dispersion, circular dichroism), or must employ a chiral environment via diastereomer formation or interaction. Recently, it has become increasingly clear that such diastereomeric relationships may already exist in nonracemic mixtures of enantiomers via self-association in the absence of a chiral auxiliary (see Section 3.1.4.7.). 

Optical Rotatory Dispersion, Circular Dichroism, and Magnetic Circular Dichroism , R. B. Homer, in Physical Methods in Heterocyclic Chemistry , ed. A. R. Katritzky, Academic Press, New York, 1971, vol. 3, pp. 397-423. 

Optical rotatory dispersion, circular dichroism, and infrared spectra of... 

ORD/CD optical rotatory dispersion/circular dichroism ordered network controlled,... 

Other methods have also been used for determining absolute configuration in a variety of molecules, including optical rotatory dispersion, circular dichroism, " and asymmetric synthesis (see p. 166). Optical rotatory dispersion (ORD) is a measurement of specific rotation, [a], as a function of wavelength. The change of specific rotation [a] or molar rotation [[Pg.160]

Electronic Spectra and Optical Rotatory Dispersion (Circular Dichroism) 191... 

Stan s some one hundred articles dealt with the synthesis, structure, stereochemistry, and biological properties of coordination compounds, including the anticancer activity of platinum complexes optical rotatory dispersion circular dichroism the Pfeiffer Effect in metal complexes inorganic nomenclature and the application of computer techniques to chemical and information problems. A prominent educator, he edited three books on inorganic and coordination chemistry. 

OPTICAL ROTATORY DISPERSION, CIRCULAR DICHROISM, AND THE PFEIFFER EFFECT IN COORDINATION COMPOUNDS... 

Perrin JH and Hart PA (1970) Small molecule-macromolecule interactions as studied by optical rotatory dispersion-circular dichroism. Journal of Pharmaceutical Science 59 431-448. 

Green, N. M., and M. D. Melamed Optical Rotatory Dispersion, Circular Dichroism and Far-Ultraviolet Spectra of Avidin and Streptavidin. J. Biochem. 100, 614-621 (1966). 

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