Tartaric acid anomalous dispersion

The experimental method used to determine the chirality or absolute structure of a molecule or crystal structure involves the use of the anomalous dispersion of X-rays by one or more atoms in the structure. We will now describe this effect and how Bijvoet used it to determine the absolute configuration of (-l-)-tartaric acid from the differences in the intensities of the hkl and iM Bragg reflections. 

To determine the absolute configuration of optically active organic compounds, there are two nonempirical methods. One is the Bijvoet method in the X-ray crystallographic structure analysis, which is based on the anomalous dispersion effect of heavy atoms. - The X-ray Bijvoet method has been extensively applied to various chiral organic compounds since Bijvoet first succeeded in determination of the absolute stereochemistry of tartaric acid in 1951. The second method is a newer one based on the circular dichroism (CD) spectroscopy. Harada and Nakanishi have developed the CD dibenzoate chirality rule, a powerful method for determination of the absolute configuration of glycols, which was later generalized as the CD exciton chirality method. 8 The absolute stereochemistry of various natural products has been determined by application of this nonempirical method. 

In 1951, the Dutch chemists J. M. Bijvoet, A. F. Peerdeman, and A. J. vanBommel, using X-ray crystallography and a new technique known as anomalous dispersion, determined that the sodium rubidium salt of (+)-tartaric acid had the RJi configuration. Because (-l-)-tartaric acid could be synthesized from (—)-glyceraldehyde, (-)-glyceraldehyde had to be the S enantiomer. The assumption, therefore, that (-l-)-glyceraldehyde had the R configuration was correct ... 

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