10 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



from the name. Thus, the 12-carbon acid commonly kno^^•n as lauric 

 acid (CH3(CH2)ioCOOH) is called by the Geneva system dodecanoic, since 

 it is derived from the hydrocarbon dodecane (CH3(CH2)ioCH3). 



The system for naming the imsatiirated acids is simple when once under- 

 stood. In all cases, the same rule holds as for the saturated acids, namely 

 that they are named after the corresponding hydrocarbon. It should be 

 recalled that in the case of the unsaturated hydrocarbons with one double 

 bond the suffix ane is replaced by ene. Thus hutenoic acid has the formula 

 CHsCHrCHCOOH (or CHaiCHCHoCOOH) and is to be regarded as a 

 derivative of the corresponding biitene. Since the position of the double 

 bond is also of importance in characterizing the compound, this must be 

 designated if the exact substance is to be defined. According to the 

 Geneva system, the successive carbon atoms are numbered, starting with 

 the carboxyl carbon as "1." Thus, CHgCHiCHCOOH would be 2- 

 butenoic acid, while CH2 : CHCHoCOOH would be referred to as 3-butenoic 

 acid. Oleic acid is thus systematically designated as 9-octadecenoic acid, 

 although some authors prefer to use the designation A^-'^-octadecenoic acid, 

 or simply A^-octadecenoic acid. In the latter case only the number of the 

 carbon atom in the unsaturated bond nearest the carboxyl group is indi- 

 cated. Another earlier practice for the designation of double bonds by 

 the Greek letters a, /3, y, etc., is entirely impractical for the long-chain fatty 

 acids with which one is concerned in natural fats. 



The procedure for the polyethenoid acids (those with more than one 

 unsaturated linkage) should also be understood, since a number of such 

 acids are of a far greater importance than would be indicated bj'' their 

 quantitative distribution. Acids with two double bonds have the suffix 

 dienoic replacing the terminal e on the saturated hydrocarbon. Similarly, 

 the suffixes irienoic, tefraenoic, and pentaenoic refer to acids with three, 

 four, or five double bonds, respectively. Linoleic acid (CH3(CH2)4CH:- 

 CHCH2CH :CH(CH2)7COOH) is referred to as 9,12-octadecadienoic acid or 

 as A^'^^'^-'i^ (or A^'i2)-octadecadienoic acid. Linolenic acid (CH3CH2CH:- 

 CHCH2CH : CHCH2CH : CH(CHo)vCOOH) is called 9,12,15-octadeca- 

 trienoic acid (or A^'^°''"''''^'^®-octadecatrienoic acid or more simply A^-'^-'^- 

 octadecatrienoic acid). 



(2) Saturated Fatty Acids 



The empirical formulas for all fatty acids in this group agree with the 

 type formula, C„H2„02. In the case of natural fats, n is, in almost every 

 case, an even number. However, this is not invariably true, as a number 

 of odd-carbon acids occur in the case of the iso acids in wool fat.^ In line 

 with this is the interesting observation of Weitkamp, Smiljanic, and 



» A. W. Weitkamp, /. Am. Chem. Soc, 67, 447-454 (1945). 



