( -^BH ) 



the qumility of the isomers, when inli-odiiciiiu Z inlo ('JI^V, wonUl 

 be expressed l>v products as p(i' cte. as shown hy the subjoined 

 scheme : 



X V' ^ 



„./\r „„./\v 



P'l 

 <1\ /'I ''\/^'' '''' 



In this it lias been supposed tliat on introdneing a second group 

 into a monosubstitnted l)enzene derivative all the three possible 

 isomers are formed, which in |>raclice will most likely be the case 

 even if the ([uantity of one of these should be so small as to be 

 generallv overlooked. In fact, in a number of cases where at first 

 only two subslituents had been found, such as in the nitration of 

 nitrobenzene, a careful inxestigation also revealed the ju-esence of a 



third one. 



The quantitative investigation as to the relative (juanlities of the 

 isomers which are formed in the nitration of substances C,H,XY 

 now^ showed that those (piantities generally diller very considerably 

 from the i)rodncts pq' etc. so that a serious diversion of the directing 

 influence on the third substitnent must be admitted. This diversion 

 was found to depend not only on the nature of the substitnents but 

 also on theii' place in the molecule as proved i>y the following 



example. 



In the nitration of chloroben/ene at tr para-, ortho- and meta- 

 nitrochlorobenzene are formed in the following (piantities: 

 (1 ., CO.,II 



/\ In that of benzoic acid /\ 



! the mtrobenzoic acids in i 



\/ ■■ the following proportion: \/ 



G9.9 '-^ 



If CO.,H and CI did not modify each other's directing influence, nitro- 

 derivatives obtained in the nitration of ortho- and metachlorobenzoic 

 acid would be formed in the (|uantities indicated in the subjoined 

 schema : 



CO.JI ^'OjH 



Cl 1 C9.9 X 1 8.5 / \ 29.8 X 18..i 



and 



G9.9X80.2\ /29.S/'80.2 \ y '^^ 



of the other i)ossible isomers only very insigniticant quantities. These 

 were in fact so trifling that they were not found. Of the two isomers 

 to be expected in both cases, the relative quantity ought to be just 

 as large as that wdiich is formed in the nitration of chlorobenzene 

 itself. Instead of this was found: 



