84 



cis-cyclopropane-dicarboxylic acid 1.2 4 X 10~^ 



trans „ „ 1.2 2.1 X 10-» 



cis-cyclobutane-dicarboxyiic acid 1.2 6.6 X 10— & 



trans „ „ 1.2 2.8 X 10-5 



cis-cyclopentane-dicarboxylic acid 1.2 1.58 X10~^ 



trans „ „ 1-2 1.2 X 10-^ 



cis „ „ 1.3 5.4 XlO-5 



trans „ „ 1.3 I 5.0 X 10-^ 



cis-cyclohexane-dicarboxylic acid 1.2 14.4 X 10^^ 



Anhydride Resolvable 



trans 

 cis 

 trans 

 ? cis 

 ? trans 



1.2 6.2 XIO-^ 



1-3 ^ / not 

 j 3 j (^determined 



1.4 3 X 10-5 

 1.4 4.6 XlO-5, 



+ 



+ 



+ 



+ 

 + 

 + 



+ 



/not investi- 

 ^ gated 



+ 



(not investi- 

 ^ gated 



} sym- 

 ( metrical 



This is the more true of tlie dissociation constants, whereof the 

 differences in ihe case of the cjclopentane-dicarboxylic acids are 

 small already, but leastways such that from the acid with the 

 greater constant an anhydride is known. 



About the cyclohexane-dicarboxylie acids in this respect we grope 

 in the dark. The J-2-acid, which has been resolved into optical antipodes 

 and accordingly is undoubtedly the trans acid, is stronger than the 

 cis acid; both acids easily form an aidiydride. If in this case it 

 should have been unknown which acid is resolvable, we should 

 probably have come to a wrong conclusion. 



With the 1-4-dicarboxylic acids, the classical case of cyclic cis- 

 trans isomerism, there is no certniniy at all; the one with (he highest 

 melting point, which von Bakyer has denominated trans, has the highest 

 dissociation constant and therefore one should perhaps call it the 

 cis acid. As it as little forms an anhydride as the isomer and neither 

 can be resolved into optical antipodes, the only remaining argument 

 in favovir of the current conception is the greater stability ; an 

 argument that should be termed weak, considering the slight solubility 

 and the high melting point. 



Still the case is not entirely hopeless; after having discussed the 



