73 
As exactly in this case trans diol is formed and a Walden inversion 
cannot otherwise take place but at the atom which determines the 
stereoisomerism, it is very probable that the change of the configuration 
takes place at the a-C-atom. 
A second observation may finally be made about the oxidation 
of cyclopentene and cyclohexene by KMnO,. Thereby, principally at 
least, the cis diols appear to be formed. From this it follows that 
the oxides cannot be the intermediate products, as these would pass 
into trans diols under the circumstances of the experiment. 
Perhaps the favoured production of ‘the cis diols by KMnO, is 
related to the formation of complex compounds of trivalent manganese. 
For on the one side it appeared that oxidation of oxalic acid by 
KMnO, also commences with the formation of these manganese 
compounds, while on the other side it was found that the «-hydroxy- 
acids are very liable to forming complex manganese compounds. In 
these compounds the hydroxyl groups are favourably situated, as 
was shown by the determination of the conductivity of mixtures 
with boric acid. Then we should have to admit here that the possibility 
of the formation of these complex compounds with cis-diols would 
exercise an influence leading to their production. 
However in that case a tendency to further oxidation of the cis 
diols is to be anticipated, just as the w-hydroxy acids are easily 
attached by mangani hydroxide. 
This would then explain the very poor yields not surpassing 20°/, : 
a closer examination however will have to clear up this matter. 
