FATTY ACIDS 391 



III. Derived Lipids — certain substances derived from compounds in the 

 above groups by hydrolysis. 



1. Fatty acids of various series. 



2. Sterols — mostly alcohols of large molecular weight, soluble in fat 

 solvents. Examples: cholesterol (C27H45OH), and ergosterol 

 (C28H43OH). Collectively the sterols found in plants are often 

 called phytosterols. 



Fatty Acids. — There are two principal groups of fatty acids, the satur- 

 ated and the unsaturated. With very few exceptions the fatty acids found in 

 living organisms contain an even number of carbon atoms. The general 

 formula of fatty acids of the saturated series is C„H2n+iCOOH. The fol- 

 lowing are the principal acids in this series: 



Formic HCOOH or CH2O2 



Acetic CH3COOH or C2H462 



Propionic CH3(CH2)COOH or C3H6O2 



Butyric CH3(CH2)2COOH or C4H8O2 



Caproic CH3(CH2)4COOH or CcHioOs 



Caprylic CH3(CH2)6COOH or CsHieOs 



Capric CH3(CH2)sCOOH or C10H20O2 



Laurie CH3(CH2)ioCOOH or C12H24O2 



Myristic CH3(CH2)i2COOH or C14H2SO2 



Palmitic CH3(CH2)i4COOH or C16H32O2 



Stearic CH3(CH2)i6COOH or C1SH36O2 



Arachidic CH3(CH2)i8COOH or C20H40O2 



The first four homologues in the above series do not commonly occur 

 In fats. Caproic, caprylic, and capric acids occur as glycerides in palm and 

 coconut oils. Laurie acid has been found as a glyceride in laurel, coconut, 

 and palm oils. Palmitic acid Is found as glycerides in bayberry wax, palm 

 oil, and many other plant and animal fats. Stearic acid Is similarly a con- 

 stituent of many plants and animal fats. Arachidic acid is found abundantly 

 as a glyceride In peanut oil. 



The molecules of the unsaturated fatty acids contain one or more pairs 

 of carbon atoms united by a double bond. Molecules of such acids are not 

 entirely "saturated" with hydrogen as they possess the capacity of combining 

 with two additional atoms of hydrogen for each double bond present. The 

 best known of the unsaturated fatty acids is oleic acid which contains one 

 double bond located at the midpoint of the carbon chain. Its formula can 

 therefore be Indicated as follows: CH3(CH2)7CH=CH (CH2)7COOH. 

 Oleic acid is the most abundant of all unsaturated plant fatty acids. 



