80 



II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



The absorption of the fatty acids in the ultraviolet results both from the 

 effect of the carboxyl group and from the unsaturated linkages. That 

 which can be ascribed to the effect of the carboxyl is apparent only at wave 

 lengths of approximately 200 m/x or shorter, whereas that due to the double 

 bonds shows various maxima in the area between 200 and 350 m^. The 



?.5 



2L0 



1.5 



WAVE LENGTH, mjU. 

 340 320 300 280 260 240 



220 210 



C 10 



05 



0.0 



O-0.5 



-1.5 



-20 



-25 



26 28 



WAVE NUMBER X 10'^ (cm.-l) 



Fig. 16. The ultraviolet absorption spectra of saturated and 

 unsaturated fatty acids. "^ 



absorption curves of a number of saturated and unsaturated acids are in- 

 cluded in Figure IG. 



Several features of the absorption curves seem to be quite consistent. 

 Maximum absorption of the t7-ans isomer as compared with the cis isomer in 

 general is shifted about 2.5 to 5 m/x (25 to 50 A.) toward the visible spec- 

 trum. 



An increase in the number of double bonds increases the absorption, 

 particularly in the shorter wave lengths. The relative intensity of ab- 



