(e) "Earlier in the 19th century, Jean-Baptiste Biot, a French physicist, discovered that [natural] tartaric acid was optically active. That is, when Biot shined polarized light (which moves out in only one direction, say vertically or horizontally, rather than [in] all directions[, as in natural light]) through tartaric acid crystals in a solution, they rotated the light clockwise or counterclockwise. But no one knew how the crystals did it. When studying the paratartaric acid [in the overheated wine; see (d) above], Pasteur found that it produced two kinds of crystals — one like those found in tartaric acid and another that was the mirror opposite. The crystals were handed, or what the Greeks call chiral (kheir [which is Greek spelling]) for hand. And they were not optically active, like the [natural] tartaric acid. Pasteur concluded that the mirror-image crystals, together as a 50/50 mix in the solution, canceled out each other's ability to rotate polarized light. And without even knowing how a molecule was built, just eight months after receiving his doctorate, he said that their molecular structure was chiral, too. Chemistry changed forever."
(i) Joseph M Hornback, Organic Chemistry. 2nd ed. Brooks/Cole, 2005, at page 238
https://books.google.com/books?i ... tweezer&f=false
("The first experiments of importance to this area were reported in 1915 by the French physicist JB Biot, who discovered that certain organic compounds, such as turpentine, sugar camphor, and tartaric acid, were optically active: that is, solutions of these compounds rotated the plane of polarization of plane-polarized light. Of course, the chemists of this period had no idea of what caused a compound to be optically active because atomic theory was just being developed and the concepts of valence and stereochemistry would not be discovered until far in the future. The next major contribution was made in 1848 by the great scientist Louis Pasteur. During the fermentation of wine, large quantities of (+)-tartaric acid precipitate in the barrels. Pasteur was studying a salt of this acid when he discovered that it has a very interesting property[: chirality] * * * Using a tweezer and a magnifying glass [some say a microscope] (and considerable patience), Pasteur was able to separate these crystals of [paratartrate]. He found one [pile] to be completely identical to the salt of (+)-tartaric acid that he had studied previously. The other had identical physical and chemical properties except that it rotated plane-polarized light in the opposite direction. Pasteur had accomplished the first resolution of a racemic organic compound!")
(ii) Peter J Ramberg, Chemical Structure, Spatial Arrangement; The early history of stereochemistry, 1874–1914. Routledge, 2017, page number not shown
https://books.google.com/books?i ... larized&f=false
("The most important of these salts for our purposes were the sodium-ammonium salts of tartaric and paratartaric acid. * * * In 1844, the German chemist Elihard Mitscherlich had noticed that these two salts [sodium-ammonium salts of tartaric and paratartaric acid] exhibited identical external crystalline forms. In fact, the two ammonium sodium salts were virtually identical except for their behavior towards polarized light. A solution of tartrate rotated polarized light, while a solution of the paratartrate had no effect. This proved puzzling, because the influence on polarized light was not reflected a difference in crystal forms. * * * he [Pasteur] perceived a crucial difference, overlooked by Mitscherlich, in the crystals of the sodium-ammonium tartrate and paratartrate. The crystals of tartrate and paratrate, Pasteur noticed, were hemihedral and asymmetric crystals that were non-superimposable mirror images of one another")
(iii) hemihedral?
(A) -hedral (adjective combining form): "having (such) a surface or (such or so many) surfaces"
https://www.merriam-webster.com/dictionary/-hedral
(B) Laurence D Barron, Molecular Light Scattering and Optical Activity. Cambridge University Press, 2004, at page 26
https://books.google.com/books?i ... ohedral&f=false
("Direct evidence that the structure of optically active materials is in some way chiral followed from the observation by Hauy in 1801 that the apparent hexagonal symmetry of quartz crystals was in fact reduced by the presence of small facets on alternate corners of the crystal. These hemihedral facets destroy the centre and planes of symmetry of the basic holohedral hexagonal crystal * * * as in Fig 1.11. The two forms of quartz which Biot had found to provide opposite senses of optic rotation were subsequently identified by Herschel (1822) as the two hemihedral forms of quartz. * * * Pasteur extends the concept of chirality from the realm of the structure of optically active crystals [quartz] to that of the individual molecules which provide optically fluid or solutions. He worked with tartaric acid * * * The crystal forms of tartaric acid and most of its salts are hemihedral, whereas those of paratartaric acid and most of its salts are holohedral")
* It is critical that one views Fig 1.11.
* Krešimir Molčanov and Vladimir Stilinović, Chemical Crystallography before X-ray Diffraction. Angewandte Chemie International Edition 53: 638-652 (2014)
https://www.researchgate.net/fig ... levorotatory-sodium
("Figure 7: Crystals of a) dextrorotatory sodium ammonium tartrate, b) levorotatory sodium ammonium tartrate, and c) optically inactive sodium ammonium racemate. While (a) and (b) are hemihedral and enantiomorphic to each other, (c) is holohedral)
The importance is that crystals of paratartrate do not have hemihedral facet, though the overall shape of crystals (of hemihedral and holohedral crystals) are dissimilar.
(C) Robert Glaser, Symmetry, Spectroscopy, and Crystallography; The structural nexus. Wiley, 2015, at pages50- 51
https://books.google.com/books?i ... ography&f=false
("Pasteur observed that one of the crystal facets was longer (hemihedral face h) than the others. This gave the sodium ammonium (+)-tartrate and paratartrate crystals an asymmetric appearance (like those of quartz) since the h-hemihedral faces (see left-handed 56 and right-handed 57). Moreover, he noted a correlation between the right-hand disposition of the elongated face and the maintenance of this asymmetry when the (+)-tartrate double salt crystals were dissolved to afford a dextrorotatory solution")
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发表于 6-21-2017 16:08:49
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