Rubidium molecules, absolute configuration

The method, also called heavy atom method, consists in introducing a heavy atom in the molecule. Then X-rays with a wave length close to the X-ray absorption of the heavy atom is introduced. As a result a phase shift is superimposed on the ordinary diffraction pattern and configuration is then deduced. The method was first employed in 1951 by Bijvoet et al. to examine sodium rubidium tartrate who concluded that it is possible to differentiate between the two optically active forms. In other words it was possible to determine the absolute configuration of the enantiomers. Since then the absolute configurations of about two hundred optically active compounds have been elucidated by their correlation with other substances of known configuration. 

In 1951 Bijvoet realized that the breakdown of Friedel s law (I j = Igjtl), which occurs when a crystal disperses X-rays of a wavelength which excites an atom in the crystal ( anomalous dispersion ), could be used to determine the configuration of a molecule absolutely. He then applied this method to sodium rubidium (-f-)-tartrate, using Zr Ka X-rays, and... 

If the crystal-structiu-e analysis is made on a derivative containing a heavy atom, with x-rays of wavelength appropriate to the particular heavy atom (that is, Br or I with CuKa radiation), it is possible to determine the absolute configuration of an enantiomorphous molecule. This method was first demonstrated with the rubidium sodium salt of dexiro-tartaric (l-threaric) acid tetrahydrate by Bijvoet and coworkers in 1951. The results confirmed the configuration of dextro-i vi nc acid originally assigned by... 

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