CONSTITUTION OF BENZENE 93 



benzene leads to the same product ; this may be expressed 

 symbolically as 



H a = H,= H c = H, (i) 



In the second place it appears that in benzoic acid there 

 are still two hydrogen atoms whose substitution leads to 

 the same result. 



Let us take e. g. the oxyacid, C G (COOH) a (OH) 6 H c _ 7 , and 

 convert the corresponding bromtoluene, C (CH 3 ) a Br 6 H c _ /? 

 into nitrobromtoluene, C G (CH 3 ) a Br 6 (NO 2 ) H 3 ; this may be 

 converted by reduction into an amidotoluene, C 6 (CH 3 ) a H b 

 (NH 2 ) H 3 , and the latter by diazotizing and treatment with 

 bromine, into C 6 (CH 3 ) a H 6 Br H 3 , which is identical with the 

 original substance. Accordingly in benzoic acid, C 6 (COOH) a 

 H 6 _/, one hydrogen atom is in a position identical with 6, 

 consequently either 



H & = H c , H & = H d , H 6 = H e , or H 6 = H/. 



The first two possibilities, however, disappear, since the 

 corresponding oxy acids that have the OH in 6, c, and d 

 respectively are different, so there remain only the 

 possibilities 



H b = H e and H 6 = H, .... (2) 



In the third place there is, besides H & , still a pair of 

 similar H atoms in benzoic acid, as appears from the fact 

 that the oxybenzoic acid in question, C 6 (COOH) a (OH) & H c _ /5 

 gives a bromobenzoic acid, C ti (COOH) ft Br 6 H c _/, which leads 

 to two isomeric nitrobromobenzoic acids, C (COOH) a Br 6 

 (NO 2 ) H 3 , whose reduction gives the same amidobenzoic 

 acid, C, (COOH) a H 6 (NO 2 ) H 3 . Thus (as again H c = H d is 

 excluded on account of the difference between the corre- 

 sponding oxybenzoic acids) either 



H c = H e , H c = H /? H, = H e , H, = H/, or R e = H 7 (3) 



If (2) and (3) are combined, remembering that equivalence 

 of b, c, and d is excluded, so that e.g. the combination 



H, = H, and H c = H e 



