Researches on the molecular asymmetry of natural organic products (1860).

  • Pasteur, Louis, 1822-1895.
Date:
1905
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Licence: In copyright

Credit: Researches on the molecular asymmetry of natural organic products (1860). Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    repeated with the other under the same conditions, and in each case we get identical, but not superposable products ; products which resemble each other like the right and left hands. The same forms, the same faces, the same angles, hemihedry in both cases. The sole dis- similarity is in the inclination to right or left of the hemihedral facets and in the sense of the rotatory power. VII. From these results, as a whole, it is evident that we have to do with two isomeric substances, whose general relations as regards similitude and molecular dissimilarity we know. Now recall the definition of a chemical species which I gave a few minutes ago :—the aggregate of individuals identical in the nature, the proportion, and the arrangement of the elements. All the properties' of substances are functions of these three terms, and the object of all our work is to pass, by investigation of the properties, to the knowledge of these three things. In isomeric bodies, the nature and proportion are the same. The arrangement alone differs. The great interest of isomerism has been to introduce into the science the principle that substances may be, and are, essentially different solely because the arrangement of the atoms is not the same in their chemical molecules. But no isomeric bodies existed whose relations in respect to molecular arrangement could be known. This desideratum was supplied for the first time by the dis- covery of the constitution of paratartaric acid, and of the constitutional relations of the right and left tartaric acids. We know, on the one hand, that the molecular structures of the two tartaric acids are asymmetric, and on the other, that they are rigorously the same, with the sole difference