1220 
‘t Horr, must really be considered only as a very favourable factor 
with respect to the mentioned possibility of such isomerism; but 
that the chemical difference of the substitutes in this ease may not 
absolutely be regarded as the predominant factor therein. 
Finally the right- and left-hand isomerism must appear possible wi 
all those cases, where, — it matters not whether the substitutes are 
equal or unequal, — the spacial arrangement in the molecule and 
the distribution of the intramolecular forces, will fulfil the special 
conditions of symmetry which can be generally deduced and formu- 
lated for all kinds of spacial systems differing from their mirror- 
images. 
$ 2. The investigations of the last few years have completely 
justified the conclusion, that in the first instance it depends in this 
question upon the spacial arrangement alone. That e.g. the differences 
of mass of the substitutes, are no measure for the lower or higher 
degree of “molecular dissymmetry”, has inter alia resulted from 
FiscHeRr’s experiments’) relating to the propyl-isopropyl-cyano-acetic 
acid, whose optically active components show a fairly high specific 
rotation (about 11°), notwithstanding the equal masses of both the 
hydrocarbon-radicals in their molecules. Furthermore Swarts tried 
to prove firstly that no other carbon-atoms need to be linked directly 
to the unsymmetric atom in such active molecules; but it was only 
recently proved in a final way by Pops, in the case of the Ammoniwm- 
salt of Chloro-jodo-methane-sulfonic acid’). 
And that also the above-mentioned isomerism can occur in cases 
where no symmetrical atoms, surrounded by unequal substituents, are 
present, was proved some years ago by the experiments of Porw, 
Perkin and Warracn *), with respect to the 1-methyl-cycloherylidene- 
4-acetic acid: 
Cc COOH 
Ne “(J Me 
a eee 
However the solubility *) of these and related substances in almost 
1) E. FrscHer and E. Frarau. Ber. d. d. Chem. Ges. 42. 981 (1909). 
*) W. J. Pope and J. Reap. Proceed. Cambridge Phil. Soc. 17 (1914); Trans. 
Chem. Soc. 105. 811 (1914). 
5) Pope, PERKIN and WaArLACH. Trans. Chem. Soc. 95, 1789. (1909): Pope and 
PERKIN, ibid. 99. 1510 (1910). 
+) According to a private communication given by Prof. PoPr to me. 
