Benzene Bamberger structure

Fig 8 3 The Bamberger structure (a) for benzene is less reasonable than a combination of two participating Kekule structures (b)... 

Bamberger s formula org chem A structural formula for naphthalene that shows the valencies of the benzene rings pointing toward the centers. bam.bor-garz for-myo-lo ... 

A theoretical understanding of furan and its congeners followed in the wake of the progress with the benzene problem, but for the five-membered heterocyclic compounds Bamberger s centric formula was always the most reasonable one, as Kekule structures could not be written at all. It is not now clear to what extent the heterocycles were really regarded as benzene analogues, but a remark made by Hantzsch, that coumarone is the furfurane of the naphthalene series was certainly percipient. Furan is variously said to be aromatic, superaromatic or not aromatic at all, for the debate continues. 

Later suggestions concerning pyridine followed closely the pattern of the history of benzene structures. Consideration of the conversion of pyrrole to 3-chloropyridine (see p. 88) led Ciamician and Dennstedt " to propose a prism formula. Riedel , from the degradation of acridine to quinoline, and thence to pyridine derivatives, supposed the diagonal structure which he had proposed for acridine (9) to persist in pyridine (10), while Bamberger (see below) suggested a centric structure (11), and a Thiele formula was also considered. 

If Kermack and Robinson srepresentation of benzene (4) restated Thiele s structure in electronic terms, it also re-interpreted Armstrong and Bamberger s ideas which were now transformed into the view that aromatic stability was associated with a sextet of electrons s. Two of nitrogen s five valency electrons were used to link the nitrogen atom to the two adjacent carbon atoms in pyridine, one contributed to the aromatic sextet, and two,... 

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