Molecular optical activity

Mason, S. F. Molecular Optical Activity and Chiral Discrimination" Cambridge University Press Cambridge, England, 1980. 

See Mason, S. F. Top. Stereochem. 1976, 9, 1 and Mason, S. F. Molecular Optical Activity and the Chiral Discriminations" Cambridge University Press Cambridge, 1982, p. 7, for an excellent discussion on Pasteur s and Laurent s early contributions to stereochemistry. 

S. F. Mason, Molecular Optical Activity and the Chiral Discriminations , Cambridge University Press, Cambridge,... 

Martinez RZ, Santos J, Cancio P, Bermejo D (1993) XXIIth European CARS Workshop, Villigcn, Switzerland, poster P27, and private communication Mason SF (1982) Molecular optical activity and the chiral discriminations. Cambridge University Press, Cambridge... 

The first theoretical model of optical activity was proposed by Drude in 1896. It postulates that charged particles (i.e., electrons), if present in a dissymmetric environment, are constrained to move in a helical path. Optical activity was a physical consequence of the interaction between electromagnetic radiation and the helical electronic field. Early theoretical attempts to combine molecular geometric models, such as the tetrahedral carbon atom, with the physical model of Drude were based on the use of coupled oscillators and molecular polarizabilities to explain optical activity. All subsequent quantum mechanical approaches were, and still are, based on perturbation theory. Most theoretical treatments are really semiclassical because quantum theories require so many simplifications and assumptions that their practical applications are limited to the point that there is still no comprehensive theory that allows for the predetermination of the sign and magnitude of molecular optical activity. 

A chiral substance is defined by the International Union of Pure and Applied Chemistry (lUPAC) as one that interacts differently with left and right circularly polarized light. Two types of molecular optical activity are recognized inherent dissymmetry characterized by large rotational strengths and inherently symmetrical, but asymmetrically perturbed, molecules for which rotational strengths are less by a factor of a thousand or so. 

We have seen (Sec. 4.8) that, like enantiomerism, optical activity results from— and only from—chirality the non-superimposability of certain molecules on their mirror images. Whenever we observe (molecular) optical activity, we know we are dealing with chiral molecules. 

This new inorganic optically active compound has several novel features. Werner s prototype, his "hexol", contained cobalt, a first-row element, and was a cation. F.G. Mann s rhodate, while an anion, contained a second row element. (+) -[Pt(S5)3]2- contains a third-row element. Further, this thioplatinate(IV) shares with the helicene hydrocarbon series the distinction of manifesting molecular optical activity while containing atoms of only two elements. Of course, enantiomorphism is well known in cryst ine binary assemblies (as in ciimabar, HgS, or quartz, Si02) and even in elements (like tellurium). 

In the past 25 years, a new area of Raman spectroscopy has evolved that is also a new form of molecular optical activity [9,11-13]. Called Raman optical activity (ROA), this form of Raman scattering applies only to chiral molecules, molecules whose mirror-image pairs are nonsuperposable. ROA is broadly defined as the difference in Raman scattering for right versus left circularly polarized (CP) radiation, where the change in the CP state of the light is effected for either the incident radiation, the scattered radiation, or both, either in phase or out of phase. The theory of ROA is more complex than the theory... 

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