83 



distinguished in this way, because they all seem lo form complex 

 compounds with basic mercury salts'). 



From the dissociation constants of amjelic and tiglic acid we can 

 at the very best suspect that in the fii'st acid a hj'drogen atom is 

 situated on the side of the COOH group, in the other one of the 

 methyl groups. 



The contigurations adopted here are supported by the consideration 

 that the most stable acid will be the one in which the relatively 

 positive group is situated as near as possible to the COOH group. 



H— C-COOH HOOC-C— H 



H-C-COOH 



maleic acid 



forms anhydride 



k= 1.2X10-2 

 complex Hg. salt -\- 



H-C COOH 



fumaric acid 



no anhydride 



9.3X10-» 







stable 



CH3-C-H 

 II 

 H-C— COOH 



iso crotonic acid 



3,6X10-5 

 



CH,-C-H 



H— C— CH-, 



H-C-CH3 



I! I II II 



H-C-COOH CH3- C-COOH CH3-C-COOH 



z-crotonic acid angelic acid tiglic acid 



2.0X10-5 



+ 

 stable 



sxio-'"^ 



1X10-5 



stable 



About oleic and elaidic acid there is utter uncertainty, because 

 the dissociation constants are not known ; it can only be suspected 

 that in the more stable elaidic acid the relatively positive carbon 

 chain is likely to lie on the side of the carboxyl group. 



With cyclic cis-trans isomers the importance of cis-trans situated 

 radicles in relation to the ring becomes less as the last widens. 

 [The conception of von Baeyer that the angle between the direc- 

 tions of the affinities of trans-situated radicles decreases as the ring 

 widens, is not incorrect; only von Baeyer deduces this decrease 

 from sterical considei'ations and then it cannot be so very important]; 

 this consideration lessens the certainty of our conclusions about the 

 configuration still more. But now here we meet with the very happy 

 circumstance, that the trans-compounds frequently are asymmetrical 

 and therefore can be resolved into optical antipodes. 



If this argument is annulled, as in the case of the hexahydro- 

 terephtalic acids, which are both symmetrical, or if a resolution into 

 optical antipodes has not been tried, there is no certainty at all. 

 This may be backed l>y the following table: (See following page). 



We see that the formation of aidiydrides, the most important 

 argument with maleic acid, has all but lost its significance in the 

 case of the cyclohexane derivatives, as both 1-2-dicarboxylic acids 

 and neither of the 1-4-acids form an anhydride. 



i) B. 33 1340, 1641, 2692, (1900); 34 1385, 2906 (I9Ü1); 35 2571 (1902); 43 

 568 (1910). 



6* 



