of the Aromatic Nucleus, 



445 



carbon atom. No exception to this rule is at present known 

 (see especially " Dix annees dans Vhistoire d'une theorie" by 

 Van't Hoff). When derived from Ladenburg's symbol, the 

 formulae for conine cannot possess an asymmetric carbon atom. 

 This is evident from the following symbols : — 



CHC,H 



3"7 



C^;C 



C H.C.H- 



From Tkoinsen's symbol. 



From Ladenburg's symbol. 



Moreover Ladenburg's theory would indicate the possible 

 existence of two position isomers derived from a-allyl 

 pyridine. 



The properties of conine, when thus considered, afford 

 direct evidence that pyridine is to be represented on Thomsen's 

 type and not on Ladenburg's. This deduction is confirmed 

 by the fact that Knorr and Antrick's researches {vide supra, 

 p. 414) prove by direct synthesis the existence of ortho-linkage 

 between the nitrogen and the a-, /3-, and y- carbon atoms in the 

 pyridine nucleus of y-oxy-quinaldine, thus : — 



c ch 3 



CH • 



(«) Pyr 



03) Pyr. 



ch c.oh (y)Pyr. 



(The proved ortho-linkages in thick lines.) 



(2) It is commonly stated that Ladenburg's symbol will 

 not account for the conjugated derivatives of benzene. This 

 is not altogether true, although there are difficulties which do 

 not exist in the case of Thomsen's symbol. 



In the case, for example, of naphthalene it is necessary to 

 sever two para-linkages and to set up an ortho-linkage in each 

 aromatic nucleus (II.). The symbol (III.) which Meyer 

 gives is complicated by the improbable supposition that the 

 atoms 3 and 3', 4 and 4', are directly linked together, and by 

 the fact that phenanthrene cannot be similarly represented 

 (vide infra). 



Phil Mag. S. 5. Vol. 28. No. 175. Dec. 1889. 2 L 



