48 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



unsaturated, we then get the series of the okfine hydrocarbons 

 of the general formula CJl^n' ^-S- •~ 



Ethylene, CjH^, 

 Propylene, CjIIg, 

 Butylene, C^Hg, etc. 



The initial member of this series should of course k 

 methylene CHj, but all efforts to prepare it result in tk 

 formation of ethylene or dimethylene. 



A further elimination of hydrogen results in the series 

 C^Hg^ _2, the initial member of which is acetylene, C2H2. 



" The next great series resulting from Kekule's generalisa- 

 tion are the ring hydrocarbons, of which the best knom 

 member is benzene. Kekul6 represented benzene by tk 

 following formula : — 



CH 



HC 



CH 

 CH 



CH 



The proof of the ring formation in benzene is a very 

 beautiful instance of the method of determimng what m 

 known as the constitutional formula of an organic compound. 

 Inasmuch as the structure of benzene as indicated by Kekule s 

 formula is a symmetrical one, it should foUow that whichever 

 of the hydrogen atoms is replaced by chlorme the same 

 monochlorbenzene should result. As a matter of fact, how- 

 ever, monocMorbenzene is prepared; only one monochlor- 

 benzene has ever been obtained. It has indeed been possible 

 by a series of reactions, too complex to be here considered, 

 systematically to replace one atom of hydrogen after another 

 in benzene, and, as has been stated, whichever atom is re- 

 placed only one monochlorbenzene results. 



A formula such as Kekul6's formula for benzene, which 



