of the Aromatic Nucleus. 



411 



derivatives. This objection was legitimate and perhaps 

 necessary, so long as our chemical formulae were 

 only convenient modes of representing atomicinter- 

 actions. We are told that instead of para-link- 

 ages there are linkages directed from the carbon 

 atoms towards the centre of the molecule, thus : — 



Not a shadow of experimental evidence is brought forward 

 to show that the valencies are of such a nature. It is difficult 

 to conceive what function such valencies have. If valency 

 means the direction along which the attractive force between 

 two atoms can be exerted, rather than a vague notion of 

 prongs sticking out from the atoms, it is hardly legitimate to 

 suppose that a carbon atom can attract or be attracted bv an 

 empty point in space. We shall not discuss the relation of 

 such a view to the " theory of open affinities," which is not 

 only in conflict with the facts of isomerism generally, but was 

 disproved by work on the isomers of propylene. It has 

 been stated that these valencies, being directed towards the 

 centre, are in a sense protected. If this is the case, and the 

 para-carbon atoms are not directly combined, it will be found 

 difficult to represent the constitution of pyrene, unless the 

 fundamental basis of modern organic chemistry — the tetra- 

 valency of the carbon atom — be given up. The formula 

 would consist of two distinct parts. These parts should 

 exist as molecular entities (0 2 and C 14 H 10 ), thus : — 



Such a supposition is not only 

 unwarranted, but opposed to all 

 that we know of pyrene. If the 

 symbol merely represents, as is 

 sometimes said, the idea that a 

 given carbon atom is directly 

 united with each of the other five, 

 it is not easy to see how its sup- 

 porters can explain the occur- 

 rence of more than one isomeric 

 di-derivative, except by the con- 

 sideration of the positions in space 

 of the atoms. What advantage 

 it would then have over that of 

 Claus I will leave to be pointed out by those who pro- 

 pounded it. 



(3) Thomsen states in his paper {Ber. xix. p. 2944) that 

 the most stable bonds in benzene are those uniting para- 

 carbon atoms, and that additive compounds are produced by 

 the severance of one or more alternate peripheral bonds. 

 A. K. Miller has shown that such a view is inconsistent with 



CH 



CH 



