4 Robinson, The Conjugation of Partial Valencies 



primary conjugation of its partial valencies, and the same is 

 true of ethyl-/3-aminocrotonate in reacting- with methyl iodide.* 





*■> + - , 2. 



• -+ 



/ 



1 



CH 3 — C CH • CO O Et 



Br-CH 2 -CH = CH-CH„-Br NHJCH 



It is important to notice that in the series : — initial compounds, 

 intermediate additive complex, final products, all the altera- 

 tions of valency are progressive. Take, for instance, the bond 

 connecting the two central carbon atoms of butadiene. In 

 the additive complex this becomes a sesqui-valency and a 

 double bond in the product, and a similar gradual change 

 will be found to be true of all the valency rearrangements 

 whether involving making or breaking of unions or the 

 transformation of single into double bonds and vice versa* 

 Therefore, by assuming the possibility of great subdivision 

 of valency, all these reactions could be represented as being 

 almost continuous and with many intermediate phases. 



The recognition of primary conjugation is rendered 

 difficult when fission follows addition although analogies are 

 usually available to assist in the determination. Thus there 

 can be little doubt, in the author's view, that the facile reac- 

 tions of aromatic phenols and amines are due to primary 

 conjugations involving the latent valencies of the oxygen or 

 nitrogen in association with the unsaturated carbon atoms of 

 the nucleus. (Cf. G. M. Robinson and R. Robinson, Trans.. 

 Chem. Soc, 191 7, 111, 964.) 



In " secondary " conjugation addition does not wholly 

 occur to the ends of the system and the existence of the condi- 

 tion is usually recognised by an orienting effect. This will 

 perhaps best be made clear bv means of an example, the 

 addition of hydrobromic acid to allyl bromide. (- = V.-HvH)-- 



* This is an unpublished observation made in collaboration with P. W. 

 Denny and for further examples of this type of addition to a conjugated 

 system Cf. — Decker, Ber. , 1905, 38, 2893; Hamilton and Robinson, trans. 

 Chem. Soc, 1916, 109, 1029; Robinson, ibid., 1039; G. M. Robinson and R. 

 Robinson, ibid., 1917, 111, 958. 



