of the Aromatic Nucleus. 



407 



(Ladenburg.) 



I. Arguments for Para-linkage. 



(1) Anthracene consists of three symmetrically conjugated 

 aromatic nuclei. This view was formerly held, but had to be 

 given up by the supporters of Kekule's theory when Anschutz 

 and Eltzbacher, in achieving the synthesis of anthracene, 

 showed that the central carbon atoms are directly linked to 

 one another (Ber. xvi. p. 623). It is now asserted that 

 anthracene consists merely of two benzene rings united by a 

 paraffinoid residue (CH — CH) IV . Several considerations 

 show that the central nucleus is truly aromatic. In the 

 first place Ramsay has shown that anthracene has, like 

 benzene, naphthalene, and phenanthrene, an abnormally low 

 molecular volume (J. C. S. 1881, p. 64). Hartley has also 

 shown that the absorption of the ultra-violet rays observed in 

 benzene is much increased in the case of anthracene as well 

 as in those of naphthalene and phenanthrene. By means of 

 oxidation the two central methenyl groups become severed 

 and converted into carbonyl groupings. The body so pro- 

 duced is closely related to the quinones and its diketonic 

 constitution has been well ascertained. The carbonyls can 

 be reduced and the methenyls reunited. Such well-marked 

 reactions are characteristic not of paraffinoid but of aromatic 

 bodies. No instance is known in which a " paraffinoid" single 



