Le Bel, Joseph Achille

(b. Pechelbronn, Bas-Rhin, France, 24 January 1847; d. Paris, France, 6 August 1930)

chemistry.

Le Bel was one of those solitary workers who make a single outstanding contribution to science and then retire into semiobscurity for the rest of a long life. His contribution was the statement of the relation of stereochemical structure to optical activity in organic compounds.

He came from a wealthy family that controlled petroleum workings at Pechelbronn, and he himself was active in managing them during the first part of his life. He was educated at the École Polytechnique, and after serving as assistant to Balard, the discoverer of bromine, in 1873 he began to work in the laboratory of Wurtz. At this time van’t Hoff was also working with Wurtz, and he and Le Bel announced the same theory almost simultaneously. Van’t Hoff’s paper appeared in Dutch in September 1874, and Le Bel’s was published in French in November of the same year; however, there is no evidence that either was influenced by the other. Each arrived at his conclusion independently at this time probably because organic chemistry had reached a point at which such a theory had become essential to further progress. The structural theory, which had so well explained many types of isomerism, had failed completely to account for optical isomers.

Between 1848 and 1853 Pasteur had shown the significance of nonsuperposable mirror images in optically active crystals, but this idea had not been extended to molecular structures even after Kekulé had explained the structures of organic compounds in terms of the tetravalence of carbon. In 1874 Le Bel, starting from the views of Pasteur, and van’t Hoff, starting from the more rigid ideas of Kekulé, arrived independently at the theory that when the four substituents around a carbon atom are different—that is, when the carbon compound is asymmetric—molecular mirror images must exist and they must show opposite optical activities. Both Le Bel and van’t Hoff used this idea to explain many cases in which such isomerism did or did not occur. Van’t Hoff subsequently shifted his interest to physical chemistry, in which he made his most important contributions; but Le Bel continued to work as and organic chemist. For a time he divided his work between his industrial activities at Pechelbronn and his chemical studies in Paris, but after 1889 he sold his petroleum interests and retired to carry on his favorite work privately in Paris. He continued to investigate optical activity. In 1891 he believed that he had found evidence for optical isomers in compounds of pentavalent nitrogen; such isomerism was later conclusively established by Pope in England.

Le Bel never held and academic appointment nor did he ever have any students. He served as president of the Société Chimique de France in 1892, and his work received general recognition in England. A conflict with members of the Académie des sciences delayed his membership until 1929, near the end of his life. In his later years he devoted himself chiefly to paleontological and philosophical studies and to botanical work in his extensive garden.

BIBLIOGRAPHY

I. Original Works. Le Bel’s works have been reprinted as Vie et oeuvres de J.–A. Le Bel, Marcel Delépine, ed. (paris, 1949). His theory was explained in “Sur les relations qui existent entre les formules atomiques des corps organiques et le pouvoir rotatorie de leurs dissolutions,”in Bulletin de la Sociéte Chimique de paris,22 (1874), 337-347.

II. Secondary Literature. Aside from the biography by Delėpine listed above, there are short obituaries by W. J. Pope in Journal of the Chemical Society (1930), 2789-2791; and bt E. Wedekind in Zeitchrift für angewandte Chemie,43 (1930). 985-986.

Henry M. Leicester

Le Bel, Joseph-Achille

FRENCH CHEMIST
1847–1930

Joseph-Achille Le Bel, born in Pechelbronn, France, was, with Dutch physical chemist Jacobus Hendricus van't Hoff, the cofounder of modern stereochemistry. They independently established the relation between optical activity and asymmetric carbon compounds.

Le Bel was born into a wealthy family that controlled the petroleum industry in Pechelbronn, Alsace. In 1865 he was sent to the École Polytechnique in Paris to obtain a chemical education and spent most of his time there doing chemical research. After graduation, he worked with the French chemists Antoine Balard and Adolphe Wurtz in Paris, in between intermediate periods of refinery construction at home. Finally in 1889, he sold his shares in the family business and established a private laboratory in Paris where he devoted himself to organic chemistry and, in his later years, paleontology, botany, and philosophy. An independent thinker who never held an academic appointment, Le Bel did manage to achieve general recognition as a chemist and even became president of the French Chemical Society in 1892.

In 1874, at the age of twenty seven, Le Bel presented a brief paper to the Paris Chemical Society that led to his scientific fame, although it may be regarded as his only outstanding contribution to the field of chemistry. By the late 1840s the great chemist and microbiologist Louis Pasteur had separated two sorts of tartrate crystals of the same composition, each crystal shape being the mirror image of the other. These crystals in solution not only rotated the plane of polarized light to a certain angle (optical activity), the rotation also occurred in opposite directions. Pasteur called such pairs of substances optical isomers , and because they showed no difference in chemical properties, they were represented by the same constitutional structural formula in the new chemical structure theory. Le Bel then extended the structure theory, from constitutional structural to configurational representations in three-dimensional space, to account for the difference in optical isomers. He argued that if a tetravalent carbon atom combined with four different groups, as in tartrate, the carbon must be asymmetric in three-dimensional space (i.e., without a symmetry plane or center). Furthermore, for each such asymmetric carbon there were exactly two different structures (stereoisomers), each being the mirror image of the other, just like the crystal shapes of Pasteur. Le Bel's structure theory could not explain optical activity, but it explained and predicted which compounds had stereo-isomers and which did not, an approach that he also extended to nitrogen compounds.

Oddly enough, van't Hoff, with whom Le Bel had worked in Wurtz's laboratory shortly beforehand, independently arrived at the same theory from a different starting point at virtually the same time.

see also Chirality; Pasteur, Louis; van't Hoff, Jacobus.

Joachim Schummer

Bibliography

Leicester, Henry M. (1973). "Le Bel, Joseph Achille." In Dictionary of Scientific Biography, Vol. VIII, ed. Charles C. Gillispie. New York: Scribners.