255 



which melts at 41 C., and was separated by Marckwald and 

 Meth 1 ) by means of the acid cinchonine-sa.\ts. 



Some remarks may be made in this connection on the isom 

 which, according to some investigators, would occur in ethylene- 

 compounds of a constitution like: 



In general such ethylene-compounds are supposed to be symmetrical 

 with respect to the plane passing through both the double-bound 

 carbon-atoms and all substitutes X, Y. Z, etc. ; the study of a great 

 number of ^Ay/^wd-derivatives seems really to have confirmed 

 this view. 



However Erlenmeyer Jr. pointed out, that in the cases 

 mentioned above, and especially in that of the isomeric, cinnamic, allo- 

 cinnamic, and iso-cinnamic acids z ), an isomerism should be possible, 

 which occasionally should create the possibility of resolving the 

 compound into optically active isomerides. It may be that a special 

 nature of the substitutes X, Y, and Z can be the cause of such an 

 exception of the rule that ethylene-derivatives have generally a 

 plan-symmetrical configuration. In any case, the problem athough 

 of high interest with respect to our views of the stereometrical arran- 

 gement of the atoms in carbon-derivatives in general, has not yet been 

 settled ; and it is to be hoped that a new and exhaustive investigation 

 of this evidently very difficult matter will be started within the 

 immediate future, which will definitely show whether we have to 

 give up our present views about the symmetry of such ethylene- 

 derivatives. 



1) W. Marckwald and R. Meth, Ber. d. d. Chem. Ges. 89. 1175. (1906)* 



2) E. Erlenmeyer Jr. Ber. d. d. Chem. Ges. 86. 2340. (1903); 88. 2562, 3496. 

 (1905); 89. 788, 1570. (1906); E. Erlenmeyer Jr., C. Barkow, and O. Herz, 

 Ber. d. d. Chem. Ges. 40. 653. (1907); E. Erlenmeyer Jr. and A. Arnold, Ann. 

 der Chemie 387. 329. (1904). C/. also: C. Liebermann and B. Halvorsen, 

 Ber. d. d. Chem. Ges. 86. 176. (1903); W. Marckwald and R. Meth, Ber. d. d. 

 nu-m. Ges. 89. 1176. 1966, 2598. (1906); E. Biilmann, Ber. d. d. Chem. Ges. 

 42. 182, 1443. (1909); 48.568. (1910); 44.3152. (1911); E. Erlenmeyer Jr. and 

 G. Hilgendorff, Biochem. Zeits. 74. 137. (1916); 77. 55. (1916). 



