ORGANIC CHEMISTRY 549 



With regard to position (i) position (4) is para, positions 

 (3) and (5) meta, and (2) and (6) ortho. The space formula 

 in which the relative positions of the electrons round the 

 carbon atoms are taken into account is not very clearly explained 

 and is too complicated to be discussed here. The author 

 considers that a static formula for benzene is demanded, but 

 seems to ignore many obvious difficulties of which perhaps the 

 most important is the separation of the ortho-positions. 

 Numerous examples of ring closure with the production of 

 benzenoid derivatives seem to be quite at variance with the 

 suggested structure. Crocker (/. Amer. Chem. Soc, 1922, 44, 

 161 8) has also applied the Lewis-Langmuir theory to the 

 benzene problem. The original conception of the cubical form 

 of the octet cell when applied to the carbon atom is not con- 

 sonant with the facts of optical activity, and there seems a 

 general tendency towards the adoption of the tetrahedral form, 

 the electrons being arranged in pairs in spite of certain theoretical 

 objections. A structure for benzene on the lines of the centric 

 formula would be represented as [xv] 



but this involves a violation of the octet principle as each 

 kernel is surrounded by only seven electrons ; moreover six 

 electrons relatively close together in the centre of the ring 

 without a positive kernel to hold them are unlikely to form a 

 stable arrangement. Accordingly the author suggests that the 

 electrons are repelled to the outside of the ring, each carbon 

 then sharing a pair of these electrons with the carbons on 

 either side [xvi]. Moreover, it is suggested that the free 

 electrons are vibrating in the plane of the ring alternately 



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