HYDROCARBONS 319 



6. Hydrocarbons 



The hydrocarbons, which reputedly are transformed with difficulty by 

 mild chemical treatment in the laboratory, are equally resistant to biologic 

 transformations. In spite of this, some hydrocarbons do represent com- 

 pounds of physiologic importance. In most cases the parent substances 

 are insoluble in water, blood, or tissue fluids. However, they may be 

 oxidized to alcohols or to acids, whereby they may become partially 

 soluble in aqueous solutions. The chief hydrocarbons which possess 

 biologic importance include both aliphatic and aromatic compounds. 

 The chemical nature and distribution of these compounds are summarized 

 in The Lipids, Vol. I, pages 400 to 404. 



{1) Aliphatic Hydrocarbons 



a. Parafl&n Hydrocarbons and Related Compounds. A chance observa- 

 tion of Chibnall and Channon,^'''''^! ^\^q^ ^j^g phosphatide fraction of cab- 

 bage leaves also contained a large amount of a white crystalline material, 

 which was shown to be a mixture of w-nonacosane and n-nonacosan-15-one 

 (di-n-tetradecylketone), led to the concept that these compounds may be 

 normal metabolic products which arise from fatty acids in the plant. 

 Thus, it was believed that two molecules of fatty acids condense to yield a 

 ketone which, on reduction, would be converted into paraffins as shown 

 below : 



R,-CH2-C00H + RjCOOH > R1CH2COR2 > RiCHjCHs-Rj 



Ketone Hydrocarbon 



R1CH2CHOHR2 > R,CH:CHR2 



Secondary Unsaturated 



alcohol hj^drocarbon 



The Possible Mechanism for the Origin of Hydrocarbons and Ketones in Plants'^i-'^a 



Clenshaw and Smedley-MacLean^^^ made a similar suggestion as regards 

 the origin of the hydrocarbon, n-hentriacontane, from spinach leaves. 



(a) The Presence of Paraffin Hydrocarbons in Plant and Insect Waxes. 

 In recent years, hydrocarbons have been found to have an especially wide 



"0 A. C. Chibnall and H. J. Channon, Biochem. J., 23, 176-184 (1929). 

 121 H. J. Channon and A. C. Chibnall, Biochem. J., 23, 168-175 (1929). 

 1" A. C. Chibnall and S. H. Piper, Biochem. J., 28, 2209-2219 (1984). 

 1" E. Clenshaw and I. Smedley-MacLean, Biochem. J., 23, 107-109 (1929). 



