Compare tlie action of diffei-eiit siibstitnents in a molecule on a defi- 

 nite bond of that same molecule. If we choose the decomposition 

 velocity of one of the pinacones as unit, the ratio of the velocities 

 of the other pinacones to this unit is then the. measure of the 

 relative labilit}'. 



Thus we obtain for thé decomposition in N/0.01 sodium etiioxide: 



for 4.4.4'.4'. tetramethylpinacone (9)= 0.1 

 4.4'. dimethylpinacone (S) = 0.18 

 4.4'. dimethoxylpinacone (7) = 0.45 

 [pinacone (1) = 1 . ] 

 2.2'.diC14.4'. dimethyl „ (10) =r 2.5 

 4,4'. dibromo „ (b) = 2.4 

 4.4'. dichloro „ (4) = 2.3 



Moreover, owing to tiie nature of the measurements we cannot 

 attach to these (inures more value than to an ap|)ro\iinate deter- 

 mination. 



4. Willi regai-d to the relative i-ednction velocity of the ketones 

 to j)inacones those experiments tell us nothing. In oi-der to get to 

 know something about this we mu.st reduce the dillerent ketones 

 under the same conditions, preferably in such a manner that nothing 

 but the pinacone is formed. 



This now mav be effected by ex[)Osing to liglit a solution of the 

 ketones in ahsohite alcohol when indeed a i-cady transformation into 

 pinacone and aldehyde takes place '). 



As it concerns here the activation of the C'-O-bond it is to be 

 expected that the relative extent of the intliience of the substituents 

 in the benzene nucleus will siiow quite a different order than in 

 the pinacone resolution. We will refer to this in a future com- 

 munication. 



LaJior. (h'(/. Chem. Tt'cJin. Un/'vo's/'fj/. 

 Delft, February 1914. 



1) This was slated long ago by Ciamician and Silber ; we liave pointed out in 

 onr previous communication lliat in this neu'.ral, or at most very fainlly acid 

 medium no transformation of pinacone into hydrole is to be expected and that, 

 therefore, the absence of hydrole in this case is again a proof that tiie reat-li 

 proper does not extend furtlier than to llie lialf pinacone molecnle. 



ion 



