255- 



COOH 



I 

 'CHOH 



CHOH 

 -CHOH 



COOH 



although a little modification of what was said above will be neces- 

 sary here, because the middle one of the three carbon-atoms is in a 

 somewhat peculiar position relative to both the others. For although 

 the carbon-atom in the midst of the molecule is not asymmetrical, 

 it has, however, an influence on the number of possible isomerides, as 

 a second inactive and non-resolvable isomeride may occur here, which 

 also is inactive "by internal compensation", but which differs from 

 the first by the interchange in space of the substitutes H and OH: 

 COOH COOH 



CHOH CHOH 



HCOH and HOCH 

 CHOH CHOH 



COOH COOH 



Of course, we shall therefore have, as in the cases of the meso-tar- 



Werner in the case of tetra-ethylenediamine-p-amino-nitro-dicobalti-bromide: 

 (Eine) 2 Co^ ^Co (Etne) 2 Br^. 



Indeed, besides the d-, 1-, and rac. compound, an inactive, non-resolvable 

 isomeride could be obtained; cf . : Ber. d. d. Chem. Ges., 46, 3674, (1913). 



Another case, in which, however, an enormously great molecular rotation was 

 observed, perhaps the greatest hitherto found, is that of tetra-ethylenediamine- 

 n-amino-peroxo-cobalti-cobalte-nitrate and its derivatives: 



III ^x^2^-\ IV 



(Eine) 2 Co ^ Co (Eine\ 



Although four optically active isomerides and two racemic compounds, according 

 to the molecular structure of the substance, may be expected, only two active and 

 one racemic form have been found. For the corresponding tetrabromide, the molecular 

 rotation was observed: [M]D = 68550. If the second cobaltum-atom be reduced 

 from tetra- valency to a trivalent atom, the rotatory power is considerably 

 diminished, and we have the same case as mentioned above, because the structure 

 of the molecule is now a symmetrical one. Cf. : A. Werner, Ber. d. d. chem. 

 Ges., 47, 1961, (1914). 



