253 



the purpose of giving full evidence that not the presence or absence 

 an asymmetric carbon-atom in the < hrmical m<>l. . ul s, but 

 rath' T the special circumstance according to which the atom 1st i< 

 configuration of the molecule as a whole has only axial symmetry or 

 not, is a predominant one for answering the question whether tin- 

 molecule may be considered as resolvable into optically a<ti\< 

 components or not. As a full proof that even the existence of no 

 carbon-atom whatever is necessary for this, we will mention here 

 Werner's dodecdmine-hexol-tetra-cobalti-bromide : l ) 



'HO 



Co(NH 3 ) t 



Co 



HO 



in which the complex: 



Co 



Br m 



evidently plays the same role 



as the tri-ethylenediamine-mo\ecu\e does in the /teo-salts mentioned 

 previously. The molecular rotatory power of the active components 

 of this substance amounts to a value of about 47600 ; its rotation- 

 dispersion is, moreover, remarkably abnormal. 



25. In this respect some other examples are of interest, which 

 are related to cases where double bonds between carbon-atoms form 

 part of the peculiarities of the molecules, or where a single carbon- 

 atom is common to two different rings. 



A case of this kind was already mentioned by Van 't Hoff, 

 namely in carbon-derivatives of the following kind: 



A \ / A 



)C = C = C< 



B/ \B 



Indeed, a closer examination of the stereometrical model of this 

 molecule will clearly show, that it is completely asymmetrical: 



Therefore its configuration must be different from its mirror- 

 image, although no true asymmetric carbon-atoms are present here. 

 Of the special case that a carbon-atom is the connection between 

 two rings, examples have been given already on page 249. 



i) A. Werner, Ber. d. d. Chem. Ges. 47. 3087. (1914). 



