PHYSICAL PKOPERTIES OF FATTY ACIDS 83 



verse holds for the higher frequency band. In the case of monoethenoid 

 acids, the cis forms show a strong infrared absorption, as noted earher, at 

 6.0 /x. This corresponds to the characteristic ethylenic band frequency of 

 1.670 cm.~\ while a similar absorption band does not occur with the trans 

 form. 



The Raman spectra of oleic, linoleic, and linolenic acids, as well as of their 

 trans forms, were determined by McCutcheon, Crawford, and Welch ^^; 

 these data are summarized in Table 29. Kohlrausch and his associ- 

 g^l^gg28o,28i have investigated the Raman spectra of several of the saturated 

 acids. 



Table 29 

 Raman Lines Characteristic of Ethyl Esters of Unsaturated Fatty Acids" 



" J. W. McCutcheon, M. F. Crawford, and H. L. Welch, Oil & Soap, 18, 9-11 (1941). 

 Frequency shifts AV are figures at left in each column; relative intensities (scale 0-10) 

 are middle figures in each column ; polarizations are listed separately at right ; p = polar- 

 ized, d = depolarized. 



Earlier studies have established the fact that the ethylenic bond of all 

 substances of the type CHR:CHR' gives rise to a band in the frequency of 

 AV 1650 for cis compounds, while the corresponding band is about AF 10 

 to 20 more for the trans isomer. Such variations are noted between the 

 oleate and the elaidate, as well as between the linoleate and the linolelaidate. 

 It is known also that a Raman line occurs in ethylenic compounds at about 

 AV 3010, which is approximately twice as intense in the cis compound 

 as in the irans compound. The corresponding intensities of the oleate and 

 elaidate at AF 3008-3009 are 6 and 3, respectively; for linoleate and 

 linolelaidate, the intensities are found to be 5 and 2, respectively. From 

 these results, it is evident that the data accumulated earlier on cis and 

 trans ethylenic compounds are applicable to the unsaturated fatty acids. 



2«« K. W. F. Kohlrausch, F. Koppl, and A. Pongratz, Z. pht/sitc. Chem., B21, 242-255 

 (1933). 



28' K. W. F. Kohlrausch, A. Pongratz, and R. Seka, Ber., B66, 1-12 (1933). 



