76 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



Long et al.-^^ studied the moiiomolecular films produced by stearic and 

 oleic acids as well as by their mono-, di-, and triglycerides. The correspond- 

 ing areas occupied per molecule were as follows: stearic, 22.5 X 10~^^sq. 

 cm.; oleic, 52; triolein, 127; and tristearin, 72. These are in close 

 harmony with the measurements of Adam and of Langmuir. 



b. Polymolecular Films. Polymolecular films have been prepared by 

 transferring the nionomolecular film on water to a glass or metallic surface 

 by a procedure described by Blodgett.-®^ A highly polished metallic sur- 

 face or foils of transparent Resoglaz have been used successfully. Even 

 or odd numbers of layers can be deposited, of any desired thickness. 

 Different polymorphic forms of the same substance can also be incorporated 

 on such films. The arrangement of the atoms can be determined by ob- 

 taining x-ray diffraction patterns-^^ or electron diffraction patterns of the 

 polymorphic films. '^^'^ 



The subject of films, particularly monomolecular ones, is discussed in the 

 monograph of Adam^®^ while Harkins-^® has reviewed the subject from 

 the thermodynamic standpoint. 



(5) Spectral Behavior of Fatty Acids 



a. Introduction. One of the most useful methods for establishing the 

 structure of the unsaturated fatty acids is absorption spectroscopy. An- 

 other related procedure which has yielded information of considerable 

 importance not obtainable by other means is the Raman spectrum. The 

 application of absorption spectra to the identification of many compounds 

 of biological interest has been one of the features in the development of 

 biochemistiy during the past decade. 



To date, spectroscopy has been of little value in the identification or 

 quantitative estimation of the saturated fatty acids. However, it has 

 played an important role in establishing the configuration of a number of the 

 unsaturated acids. Absorption spectra have been very useful in indicating 

 the position of double bonds and determining their number. The absorp- 

 tion of specific wave lengths is governed by certain characteristic groupings 

 of the molecule, which possess the same electronic, vibrational, or rotational 

 properties as are associated with energy of a given frequency. 



261 J. S. Long, W. W. Ivittelberger, L. K. Scott, and W. S. Egge, Ind. Eng. Chem., 21, 

 950-955 (1929). 



262 K. B. Blodgett, J. Am. Chem. Soc, 57, 1007-1022 (1935). 



263 L. H. Germer, "Arrangement of Molecules in Unimolecular and Multimolecular 

 Layers," in Recent Advances in Surface Chemistry and Chemical Physics, F. R. Moulton, 

 ed., Am. Assoc. Advancement Sci., Pub. No. 7, Science Press, Lancaster, Pa., 1939, 

 pp. 47-53. 



264 L. H. Germer and K. H. Storks, /. Chem. Phys., 6, 280-293 (1938). 



266 N. K. Adam, The Physics and Chemistry of Surfaces, 3rd ed., Oxford Univ. Press, 

 London, 1941. 



266 W. D. Harkins, Chem. Revs., 29, 385-417 (1941). 



