PHYSICAL PROPERTIES OF FATTY ACIDS 



81 



sorption at 210 m/x has been shown by R. H. Barnes et al.^''^ to be as follows: 

 stearic acid (0 double bonds) 60; oleic acid (1), 180; methyl linoleate (3), 

 2500; methyl linolenate (3), 10,000; and methyl arachidonate (4), 14,500. 

 The comparative absorption curves for these acids are given in Figure 17. 

 Another pronounced effect on absorption in the ultraviolet area of the 

 spectrum is caused by conjugation. The intensity of the absorption is 

 markedly increased, as is demonstrated by the higher values obtained for 



2500 



2400 2300 „ 2200 



WAVE LENGTH. A 



2100 



Fig. 17. The log of molecular extinction coefficients (e) plotted against wave 

 length for methyl arachidonate (1), methyl linolenate (2), methyl linoleate (3), 

 oleic acid (4), and stearic acid (5).^^* 



the two conjugated forms of Cig diethenoid acids studied (9,11- and 10,12- 

 octadecadienoic acids) as compared with ordinary linoleic acid (9,12-octa- 

 decadienoic acid) where the bonds are not conjugated. Similar variations 

 are to be noted between the non-conjugated trienoic acid, linolenic (9,12,15- 

 octadecatrienoic acid), as compared with the conjugated form, elaeostearic 

 acid (9,11,13-octadecatrienoic acid). The maximum absorption for the 

 conjugated diene acids was found to be at 230, for triene acids at 270, and 

 for the tetraene conjugated acid (parinaric) at 308 to 320 m/x. 



The absorption in the Schumann region is intense for the saturated acids; 

 acetic, caprylic, and myristic acids have maxima at 205 m/x and below 



278 R. H. Barnes, 1. 1. Rusoff, E. S. Miller, and G. O. Burr, Ind. Eng. Chern., Anal. Ed., 

 16, 385-386 (1944). 



