An introduction to chemical crystallography / by P. Groth, Authorised translation by Hugh Marshall.

  • Groth, P. (Paul), 1843-1927.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to chemical crystallography / by P. Groth, Authorised translation by Hugh Marshall. Source: Wellcome Collection.

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    rotation caused by the molecules (i.e., by the mode of inter¬ penetration of the point-systems in the crystal), and, on the other hand, with the crystal rotation, which is combined with the other when, to the enantiomorphism of the mode of inter¬ penetration of the point-systems, there is added an enantio¬ morphism inherent in these themselves. As a matter of fact, this appears generally to be the case ; and when the mole¬ cular rotation, as obtained either by direct measurement on the amorphous (fused) substance itself, or by calculation from the rotatory power of the solution, is compared with the rotation observed on the crystals, it is found that the latter effect is derived principally from the crystal rotation. According to the investigations of H. Traube,1 the rotatory power of matico camphor, C12H.20O, referred to unit density, is, for i mm., in the amorphous state, -0-29°; and in the crystallised state, - 2-07. The corresponding values for cinchonine antimonyl tf-tartrate, 2(C19H22N20, SbC4H407), 5H20, are : +4-14° and+ 9-79°; for zinc hydrogen malate, Zn(HC4H405)2,2H20, the values are: - 0-55° and - 3-02°. In the case of rubidium ^-tartrate the crystals are laevo-rotatory, aD = - 10-24°, while the molecular rotation of the amorphous substance is +0-69°. Since the latter possesses the opposite sign, the actual crystal rotation in this case amounts to - 10-93°. Similarly, the rotatory power of sucrose, Q2H22O11, is, according to Pocklington,2 much stronger in the crystallised state than in the amorphous state. On the other hand, the rotatory power both of patchouli camphor, C15H260, and of laurel camphor, C10H16O, has been found to have about the same value as the molecular rotation, and therefore appears to result essentially from the latter. In accordance with the view developed for optically active substances, the crystal structure of a racemic carbon compound is to be viewed thus : Since the “ asymmetric carbon atoms,” which are surrounded by the other atoms in an enantiomorphous arrangement, must consequently possess different orientations, they necessarily form an 1 Zeits. f, Kryst. 1894, 22, 50 ; 1899, 31, 624. 2 Phil. Mag. 1901 [6], 2, 361 ; Zeits. f Kryst. 37, 292.