2 Robinson, The Conjugation of Partial Valencies 



and the loop, it is supposed, can be opened up in stages with 

 the result that two partial valencies of opposite sign are 

 produced. This condition of affairs may be expressed by the 

 symbol : — 



— N" 



The chlorination of methane may be given as a simple illus- 

 tration of the representation of a reaction in accordance with 

 the above postulates : — 



{A). Reaction between two activated molecules. 



CH 8 CI 



+ I 

 CI 



CH, CI 



CH,""C1 



H 



+ 



CI 



H 



CI 



CH," CI 



H 



CI 



(B). Reaction between an activated molecule and a neutral 

 molecule. 



+ 



CH, ""CI 



+ 



H 



...CI 



CH. 



H 



: + 



CI 



.CI 



CH 3 

 H ... 



Cl 





CH 3 



-ci 





— > 



+ 





CI 





H 



Cl 



In passing it may be remarked that the role of a catalyst must 

 very often be to produce activated molecules by the formation 

 and subsequent decomposition of additive complexes. Thus 

 in catalytic hydrogenation the hydrogen may be able to form 

 a loose addition compound with nickel or palladium by the 

 aid of a degree of dissociation so small that reaction with a 

 substance containing an ethylene linkage cannot be effected. 

 This compound on decomposition, however, may be assumed 

 to liberate a strongly polarised hydrogen molecule, which is 

 highly reactive and is capable of direct union with unsaturated 

 •substances. 



Hi i i i H 



H 



H 



H 



H 



H 



H 



(Catalyst 

 surface) 



