216 THE INCOME OF ENERGY 



H H 



\ / \ / 



c = c c = c 



/ \ / X 



-C C- H-C C-H 



^ // \ // 



C - C C - C 



/ \ / \ 



TT TT 



BENZENE NUCLEUS 



OR RING BENZENE 



The benzene ring is not easily opened, but deriva- 

 tives of benzene may be readily obtained by replacing 

 hydrogen atoms. Thus, in aniline or amido-benzene, 

 C 6 H 5 .NH 2 , one hydrogen atom is replaced by amide 

 radical ; in carbolic acid, or phenol, C 6 H 5 .OH, by 

 hydroxyl ; in toluene or methyl benzene, C 6 H 6 .CH 3 , 

 by the radical CH 8 . The carbon atom in methyl 

 benzene is not a part of the benzene ring, but is 

 chained to the side of the ring. The hydrogen atoms 

 in the side-chain differ in their affinities from those 

 attached to the ring ; the hydrogen in the ring may 

 be replaced by groups (e.g. N0 2 ) which will not readily 

 replace the hydrogen of the side-chain. This is a 

 matter of special interest in relation to the specific 

 action of poisons, ferments, etc. By substituting 

 hydroxyl for the hydrogen of the side-chain, benzyl 

 alcohol, C 6 H 6 .CH 2 .OH, is formed. By introducing 

 carboxyl, benzoic acid, C 6 H 6 .CO.OH, is obtained. It 

 has been shown above that benzoic acid and glyco- 

 coll are united in the kidney to form hippuric acid. 

 Glycocoll is amido-acetic acid, CH 2 (NH 2 ).CO.OH. It 



