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Johannes Martin Bijvoet
Johannes Martin Bijvoet (23 January 1892, Amsterdam – 4 March 1980, Winterswijk) was a Dutch chemist and crystallographer at the van 't Hoff Laboratory at the University of Utrecht. He is famous for devising a method of establishing the absolute configuration of molecules.
Additional recommended knowledge
The concept of tetrahedrally bound carbon in organic compounds stems back to the work by van 't Hoff and Le Bel in 1874. At this time, it was impossible to assign the absolute configuration of a molecule by means other than referring to the projection formula established by Fischer, who had used glyceraldehyde as the prototype and assigned randomly its absolute configuration.
In 1949 Bijvoet outlined his principle, which relies on the anomalous dispersion of X-ray radiation. Instead of the normally observed elastic scattering of X-rays when they hit an atom, which generates a scattered wave of the same energy but with a shift in phase, X-ray radiation near the absorption edge of an atom creates a partial ionisation process. Some new X-ray radiation is generated from the inner electron shells of the atoms. The X-ray radiation already being scattered is interfered with by the new radiation, both amplitude and phase being altered. These additional contributions to the scattering may be written as a real part Δf' and an imaginary one, Δf". Whereas the real part is either positive or negative, the imaginary is always positive, resulting in an addition to the phase angle.
In 1951, using an X-ray tube with a zirconium target, Bijvoet and his coworkers Peerdeman and van Bommel achieved the first experimental determination of the absolute configuration of sodium rubidium tartrate. In this compound, rubidium atoms were the ones close to the absorption edge. In their later publication in Nature, entitled Determination of the absolute configuration of optically active compounds by means of X-rays, the authors conclude that
"The result is that Emil Fisher's convention, which assigned the configuration of FIG. 2 to the dextrorotatory acid appears to answer the reality."
The determination of absolute configuration is nowadays achieved using "soft" X-ray radiation, most often generated with a copper target. Despite being often the ultimate proof, other techniques such as 2D-NMR and circular dichroism spectroscopy are often used as faster alternatives.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Johannes_Martin_Bijvoet". A list of authors is available in Wikipedia.|