88 



and from this the cis conügui-atiori could be deduced for the first 

 mentioned diol. If this method had not come to the rescue, the case 

 would have been almost hopeless, because a resolution into optical 

 antipodes cannot enlighten us: 



OH 



O// 



OH 



OH 



For it is evident that both isomers are asymmetrical and therefore 

 can be resolved into optical antipodes. 



It has been our intention to draw attention to the fact, that as 

 soon as valencies are attacked of atoms which determine the stereo- 

 isomerism, the arrangement of the groups runs a risk of being 

 changed. Of course the phenomenon going b}-^ the name of Walden's 

 inversion ought also to be included here. In many cases the possible 

 isomers are both formed and very often principally the one, which 

 we should not expect. 



This will not occur only with reactions as have been mentioned, 

 by which stereoisomers are formed; in consequence of the formation 

 of stereoisomeric substances, which can distinctly be discerned, the 

 phenomenon was observed here as well as with the inversion of 

 Wai,den. But it stands to reason that it is of a general character 

 and that we may compose the rule: 



During a chemical reaction, by which atoms are added, eliminated or substi= 

 tuted, there is always a chance that the arrangement is changed of the 

 valencies of the atom or of the atoms, at which the reaction takes place. 



It deserves further consideration to establish whether the arrangement 

 around adjacent atoms or around remote atoms is disturbed, when 

 such a change occurs with the valencies of some atom. 



This is not probable fortunately, as it would highly aggravate 

 our task to determine the configuration of compounds, for every 

 relation between optically active substances would fail. Besides the 

 formation of anhydrides of maleic or citraconic acid would be worthless 

 and the differences, that may be observed in the influence of compounds 



