Eobeetson. — Molecular Complexity of Fatty Acids. 459 



characterized by their sparing solubility. On introducing an 

 alkyl group, however, the compounds are rendered much 

 more soluble, and can therefore in most cases be examined 

 (see under " Solubilities," p. 463). 



Of the groups examined, carboxyl exerts, in general, the 

 most influence, always increasing the rate of association of 

 the monocarboxylic acid from which it is derived. The mag- 

 nitude of the change is clearly seen in the case of the isomeric 

 acids — ethylmalonic and methylsuccinic. 



/ Ethylmalonic. 



CH 8 . CH 2 



CH a 



Butyric. 



•CH 2 



CH - 

 20 



C0 9 H 



CH(CO„H), 

 44 



Methylsuccinic. 



CH, • CH • CO,H 



Isobutyric. 



CH 3 ■ CH • C0 2 H 



I 

 CH., • C0 2 H CH 3 



67 ) (10-14) 



In ethyl malonic the two carboxyls are attached to an 

 isocarbon atom, but in methylsuccinic acid one is united to an 

 iso and the other to a carbon united to two atoms of hydro- 

 gen. As would be expected, the association is more rapid in 

 the latter case. In sebacic acid the carboxyls are much fur- 

 ther separated, and the mutual influence of the two groups is 

 thus less noticeable. 



Nonylic. Sebacic. 



H(CHo), • COoH COoH • (CH 2 ) 8 ■ C0 2 H 



(11) 23 



If the a hydrogens are replaced, the mutual effect of the 

 carboxyls is much diminished. This is seen in the case of 

 dibrommethylsuccinic acid, which associates only at the rate 

 of 16 per cent. 



Methylsuccinic. Dibrommethylsuccinic. 



OH. • C0 2 H CBr 2 ■ C0 2 H 



CH, 



CH 

 67 



CO.H 



CH, 



CH • C0 2 H 

 16 



Oxy and Nitroso Acids. — In phenol solution the molecular 

 depressions of hydroxyl compounds tend to increase with 

 rising concentration ; but a hydroxyl group increases the 

 association of an acid. From this it seems probable that 

 there is some mutual influence between the two groups, as a 

 diminution of the rate of association is to be expected. This 

 being so, there is reason to expect that the hydroxyl would 

 have less and less effect the further it is removed from the 

 carboxyl group. 



