84^ 



only then wlieii it is placed in tlie ortho- or the paraposition in 



regard to a nitro-ftronp. Of the isomerides 



Cl VI Cl I I (.1 CI 



sX(X, X\ /\bi /\l5r / NBr NO.,/ NBr 



XOo 



III 



xo.. 



IV 



NO., 



VI 



Br Br NO.^ 



I, IV and VI only cliloriiic, of II, 111 and V only bromine will be 

 replaced by OCH3. Hence, if we determine the proportion in which 

 chlorine and bromine are split off from the nitration prodnct of 

 ^?-chlorobromobenzene and from that of o-chlorobromobenzene, we 

 get at once the proportion wherein in the first nitration product 

 I and II are present in the second one IV -|- VI on one side. Ill -f- V 

 on the other side. This method has also the considerable advantage 

 that all the isomerides for the construction of the fusion lines 

 now need not be prepared individually and that in the nitration 

 products the various isomerides need not be separated ; this latter 

 attempt in particular would, presnmabh, have failed owing to 

 insuperable obstacles. 



The results obtained are as follows: 



j^itrationproduct of p-ddorobromobenzene contains 45.27o of the 



Cl 



/i\nOo 



compound 



3 



Br 



and 54.87o of the isomeride 1,3,4. 



Cl 



Cl 



jSilr. product of o-chhrohenzene consists of o5.57o of 



Br NOi 



+ 



Br 



NO.^ 



and of 44.57„ of 



Cl Cl 



Br 



+ 

 NO.. NO., 



; or in molecular proportion 1 : 0.80» 



The substitution velocity caused by chlorine and bromine when 

 present together in the benzene nucleus is therefore as 1 : 0.80. 

 When calculating this pro|)ortion from the composition of the nitration 

 product of />-chlorobromobenzenc it must be remembered that in the 

 nitration of chlorobenzene there is formed 30.1° „ of the c-compound, 

 but in that of the broinobenzene 38.3"/o of the same. If we call 

 .7' the ratio of the xelocities caused by chlorine and bromine we have 



30.1 : 38.3.^' = 45.2 : 54.8, 



5(3 



Proceedings Royal Acad. Amsterdam. Vol. XVil 



