of the Aromatic Nucleus. 



CH 



A 



447 



CH 



CH 



Pyrene, C ]6 H I0 (from Meyer's symbol). 

 Compare with p. 410. 



(3) It is generally admitted that closed chains of more than 

 six atoms do not exist. If this be so, it is difficult to account 

 for the constitution of fluorene on Ladenburg's theory, as it 

 is then necessary to assume the existence of a closed chain of 

 seven carbon atoms. In the formulation of this body from 

 Thomsen's symbol this ring consists of five carbon atoms only. 

 The relationship of fluorene to phenanthrene, through diphe- 

 nylene ketone and diphenic acid, proves it to be a di-ortho- 

 compound. The argument is evident from the following 

 symbols : — 



CH 2 



CH 



:h c c ch 



\A7 



CH 



CH 



CH" 



■CH 



CH' 



CH 



Fluorene, C- 3 H 10 

 (on Ladenburg's symbol). 



Fluorene, C l3 H 

 (on Thomsen's symbol). 



In this connexion I may quote the following passage from 

 Watts' ' Dictionary of Chemistry' (new edition, i. p. 800) :- — 

 " Ortho-compounds readily give rise to products of condensa- 

 tion in which the side chains may be supposed to be joined in 

 the form of a ring ; this tendency is observed to some extent 

 in the para-series but not at all in the meta-series." 



(4) The analogies between the ortho- and para-derivatives 

 of benzene as opposed to the meta- have been cited by 

 Koerner (J. C. S.1876, i. p. 240) and by Lellmann {Ber. xvii. 



2 L 2 



