The Origin of Optical Activity

These same compounds also illustrate a second important principle  

A method based on the measurement of optical rotation at many different wavelengths, called optical rotatory dispersion, has been used to correlate configurations of chiral molecules. A discussion of the technique of optical rotatory dispersion, however, is beyond the scope of this text. 

Shown below is the configuration of (H-)-carvone. (+)-Carvone is the principal component of caraway seed oil and is responsible for its characteristic odor. (—)-Carvone, its enantiomer, is the main component of spearmint oil and gives it its characteristic odor. The fact that the car-vone enantiomers do not smell the same suggests that the receptor sites in the nose for these compounds are chiral, and that only the correct enantiomer binds well to its particular site (just as a hand requires a glove of the correct chirality for a proper fit). Give the correct (R) and (S) designations for (+)- and (—)-carvone. 

Molecules that are not chiral cause no difference in velocity of the two circularly-polarized beams hence there is no rotahon of the plane of polarized hght described by their vector sum. Achiral molecules, therefore, are not ophcahy active. 

There is net rotation if (f )-2-butanol is present predominantly or exclusively, (c) 

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Until recently, the phenomenon of chirality has been better known as optical isomerism, and configurational isomers that are enantiomers were referred to as optical antipodes. The reasons for this are mainly historical. It was discovered early in the nineteenth century that many compounds, whether solid, liquid, or gas, have the property of rotating the plane of polarization of polarized light and can be said to be optically active. A satisfactory explanation of the origin of optical activity came much later and developed in its modern form from the classic researches of Louis Pasteur, and from the concept of the three-dimensional carbon atom expressed independently by J. H. van t Hoff and J. A. Le Bel.2... 

Peter Schuster Commentary On The Origin of Optical Activity 109... 

Optical activity arises from a dissymmetric stmcture of matter. Before we discuss the origin of optical activity in detail, we recall the equations of nature of light. 

Kavasmaneck P R. (1978) Asymmetric adsorption by quartz a model for the origin of optical activity, Diss.Thesis, Stanford Univ., 246 pp., Diss. Abstr. Int. B. 36 (9) 4508-4509 Chem. Abstr. 1976,84,146534. 

Klabunovs i E.I. and Thiematm W. (2000) The role of quartz in the origin of optical activity on Earth, Origins Life Evol. Biosphere 30, 431-434. 

Harada K. (1977) The recent studies on the origin of optical activity. Kagaku no Ryoki, 31, 1-11. 

Harada K. (1980) The origin of optical active compounds and their SYolution, Kagaku Sosetsu, 30, 145-153. 

Klabunovskii E.I. and Thiemann W. (2000) The role of quartz in the origin of optical activity on Earth, Origin Life Evol. Biosphere 30, 431-434. Bonner W.A. (1996) The quest for chirality. Physical origin of homochirality in life, Amer. Inst. Phys. Conf, Santa Monica CA, Febr. 1995, Proceedings, Cline D.B. (ed.). Press Woodbury, N.Y., p. 17-49. Avalos M., Babiano R., Cintas P., Jimenez J.L. and Palacios J.C. (2000) Chiral autocatalysis where stereochemistry meets the origin of life, Chem. Commun. 887-892. 

The origin of optical activity in molecules often reduces to the question of how the molecule acquires the electronic properties expected of a chiral object when it is formed from an achiral object. Most often an achiral molecule becomes chiral by chemical substitution. In coordination compounds, chirality commonly arises by the assembly of achiral units. So it is natural to develop ideas on the origins of chiral spectroscopic properties from the interactions of chirally disposed, but intrinsically achiral, units. Where this approach, an example of the independent systems model, can be used, it has obvious economic benefits. Exceptions will occur with strongly interacting subunits, e.g., twisted metal-metal-bonded systems, and in these cases the system must be treated as a whole—as an intrinsically chiral chromophore. ... 

The origin of optical activity in metal chelates is not well understood. Circular dichroism spectra, together with other physical methods, should give detailed stereochemical and conformational information which might provide a basis for theoretical advancements. 

Exceptions to the lack of use of QFT in chemistry include the work on the origins of optical activity (Barron 1982). 

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