Volume 1

Recent advances in organic chemistry / by Alfred W. Stewart.

  • Alfred Walter Stewart
Date:
1927
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Recent advances in organic chemistry / by Alfred W. Stewart. Source: Wellcome Collection.

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    Ladenburg adduced the supposed parallel cases of crotonic and vinyl-acetic acids, which differ in the position of the double bond with reference to the carboxyl group— CH3—CH : CH—CO OH Crotonic acid. CH2 : CH—CH2—COOH Vinyl-acetic acid. He alleged that if the shift of a linkage made no change in benzene, it should be equally without effect in the case of these two substances. But as they actually existed in isomeric forms, the same was to be expected in benzene, if the Kekule theory were correct. Ladenburg was answered by Kekule,1 also by Victor Meyer.2 The latter pointed out that while in benzene the only difference between the two hypothetical isomeric forms was produced by a mere change in the grouping of linkages, the cases of the two acids shown above were further complicated by the fact that a hydrogen had also shifted its position from the end of the chain to the carbon atom next the carboxyl group. Thus the cases of benzene and the unsaturated acids are not really analogous at all. Kekule attacked the Ladenburg view from a different stand¬ point, as follows :—• “ The atoms of the systems which we call molecules must be considered to be continually in motion. This view has often been expressed by physicists and chemists, and I have already discussed it in my handbook. Hitherto no explanation as to the form of this intramolecular motion has been given, as far as I know. Chemistry must, at all events, bring forward the claim that such a mechanical hypothesis accounts for the law of the linking of atoms. A planetary motion seems, therefore, not inadmissible ; the movement must be of such a kind that all the atoms forming the system retain the same relative arrangement—in other words, that they return to a mean position of equilibrium. If we now select from the numerous conceptions which may be formed, that which gives the most complete account of the chemical claims and which coincides most closely with the hypothesis of modern physicists as to the mode of the motion of molecules, the following assumption will appear the most probable. “ The simple atoms of the system approach each other in what may be considered a straight line, and rebound like elastic bodies. What we call valency would then have a mechanical meaning. Valency is the number of contacts experienced by one atom on the part of other atoms in unit time. In the same time that the monad atoms of a diatomic molecule 1 Kekule, Annalen, 1872, 162, 87. 2 V. Meyer, Annalen, 1870, 156, 265; 1871, 159, 24.
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