COMPOSITION OF NATURAL FATS AND OILS 217 



proposed: the monoacid theory, tluit of "even" distribution, and that of 

 random arrangement. However, Doerschuk and Daubert-^" have recently 

 proposed a new hypothesis, the "partial random theory," Avhich seems to 

 have excellent experimental evidence to support it. 



(fl) Monoacid Theory. This hypothesis predicates that like acids are 

 associated with each other in the triglyceride molecule to give simple tri- 

 glycerides. Although this suggestion is interesting historically inasmuch 

 as it represents the first postulated structure for fats made by ChevreuP^ 

 a century and a quarter ago, Berthelot^^ early disputed it and suggested that 

 fats most probably contain mixed triglycerides. This theory has long 

 since been abandoned by most fat chemists. The inability to isolate more 

 than traces of simple triglycerides from relatively large amounts of na- 

 tural fats cannot be harmonized with the monoacid theory. Moreover, 

 the demonstration of the widespread distribution of mixed triglycerides in 

 the natural fats has proved conclusively that triglycerides other than 

 simple ones can occur. 



(6) Theory of "Even" Distribution. The most widely accepted theory 

 at the present time is the "even" distribution theory of Hilditch.^^ Ac- 

 cording to this hypothesis, there is a tendency for the unsaturated acids to 

 be associated with a large proportion of the saturated acids and thus to 

 have as wide a distribution in the triglyceride molecule as possible. Collin 

 and Hilditch-^^ have named this tendency the "association ratio." This 

 proportion is defined as the ratio of the moles of saturated fatty acids to the 

 moles of unsaturated acids which occur in the mixed triglycerides. In fats 

 in which the amount of saturated fatty acids exceeds 60% of the total, the 

 figure for the association ratio is remarkably constant at between 1.3 and 

 1.4 to 1. 



The general principle of "even" distribution was first pronounced by 

 Bhattacharya and Hilditch,-^^--*^ in 1930, to be applicable to most vegetable 

 fats. It was shown that no appreciable quantities of completely saturated 

 triglycerides appear until the saturated fatty acid fraction makes up 60% 

 or more of the total fatty acid content (expressed on a molar basis) . When 

 the saturated acids vary from 59 to 94% of the total acids, increasing pro- 

 portions of simple triglycerides are present, but the ratio of saturated to 

 unsaturated acids remains practically uniform at 1.4:1, instead of pro- 

 gressively rising as one might expect. Such an "association ratio" cor- 

 responds to a mixture of 3 moles of monounsaturated-disaturated triglyc- 

 erides (GS2U) and 1 mole of monosaturated-diunsaturated compound 

 (GSU2) . These relationships are illustrated in the data assembled in Table 

 17, following, and are plotted in Figure 1 on page 220. 



According to the "even" distribution scheme, when a saturated acid, A, 



2" R. Bhattacharya and T. P. Hilditch, Proc. Roy. Soc. London, A 129, 468-47G (1930). 

 2" R. Bhattacharya and T. P. Hilditch, /. Chem. Soc, 1931, 901-907. 



