Structure of Simpler Organic Compounds. 137 



which thus acquires great stability. The formula would 

 be then represented as follows : 



A 



The actual constitution of benzene has been the subject of 

 a large number of controversies, which need not be dis- 

 cussed in this place, and various alternative formulas have 

 been suggested. With the adoption, however, of the first 

 formula, which, by omitting the symbol for carbon, may 

 be written 



H 



the relationship of the various benzene derivatives to one 

 another may be sufficiently well indicated. For the theory 

 of the constitution and the considerations relating to the 

 dynamics of the formula reference must be made to text- 

 books on organic chemistry. 



It now remains to substantiate the above formula. 



It will be observed that it is quite symmetrical, and 

 that every hydrogen atom is of equal value. From this it 

 should follow that not more than one mono-substitution 

 product of benzene is possible when a hydrogen atom is re- 

 placed by another group. In actual practice this had been 

 found to be the case ; there is, for example, only one mono- 

 brom benzene, C 6 H 5 Br, known, and only one mononitro- 

 derivative, C 6 H 5 (N0 2 ). It is found, thus, that the assump- 

 tion of the equal value of all hydrogen atoms is correct. 



