87 



the number of isomers, tliat in acetylene derivatives the substituents 

 lie in a line with the carbon atoms of the acetylene skeleton. 



The researches in this field, viz. the catalytic hydrogenation of 

 diphenols with the aid of nickel, show, that a mixture of thecyclo- 

 hexanediols is formed ; a reduction under the influence of platinum 

 or palladium at a low temperature apparently has not been executed yet. 



Now there are general syntheses of these diols, viz. from the non- 

 saturated cyclic hydrocarbons, either by direct oxidation by KMnO^ 

 or via the oxides; we have made use of them to prepare the hydrindene- 

 diols. According to current ideas the cis diol should be formed 

 exclusively by this reaction^): 



H 



Fig. 1. 



Indene oxide was hj'drated as mildly as possible, that is to say 

 at the ordinary temperature in aijueous solution with a very little 

 acetic acid, and still we could isolate a considerable proportion of 

 the trans isomer too. At this hydration likewise a valency of one of 

 the carbon atoms that determine the configuration, is violated and 

 a partial inversion takes place. 



In judging the cis-traiis isomerism in this case, the determination 

 of the acidity is left out for the present, as the methods of investi- 

 gation are not sensitive enough. The forming of an anhydride too 

 cannot yield a good result here, because the bearers of the stereo- 

 isomerism are brought into play, which is not the case with the 

 formation of anhydrides of acids, as of maleic or cumaric acid. 



Here are only left 1. the resolution into optical antipodes, but 

 this will not be easy and has never been successfully accomplished ; 

 2. the formation of complex compounds, which has proved effectual 

 with the sugars, as we came to know by it the contigurations of 

 «- and /?-glucose, of a- and /?-fructose and of a- and /^-galactose. In 

 the case under consideration too the last method has been to the 

 purpose; (he isomer melting at the lower temi)erature namely, 

 increased the conductivity of boric acid, on the other hand the 

 isomer with the higher melting point diminished it in some degree. 



1) Vers!. Kon. Akad. v. Wet 26, 1272 (1918). 



