Ladenburg prism formulae

It is true there are still more configurations possible such as the centric formula and three Ladenburg prism formulae projected on to a plane, but it can be shown that these can be regarded as superpositions of the five configurations mentioned above. 

The puzzling behavior of benzene, its unreactivity, and the inference that all six carbon atoms must be linked in the same way could not be described by an open carbon chain (or vertebrate), nor was it satisfactory to write one true "rational" formula for "empirical" C6H6 benzene. Albert Ladenburg s nonplanar prism formula was the best single representation,... 

Ladenburg Formula.— Ladenburg, however, not satisfied with Kekule s formula suggested another known as the prism formula. 

For a time the prism formula VI, proposed in 1869 by Albert Ladenburg of Germany, was considered as a possible structure for benzene, on the grounds that it would yield one monosubstitution product and three isomeric disubstitution products. 

My last example is a long poem (forty-one stanzas) entitled "Disputation (Frei nach Heine)" by Otto Witt, depicting the battles that had been fought during the previous dozen years, mostly in the Berichte, over the formula for benzene, namely between Kekule s hexagon and Ladenburg s prism formula. Witt s extended metaphor is that of a medieval tournament. 

In the second paper he said these are not three formulae but only one in different positions . The projection form IV is really the same as Claus s formula III V is Ladenburg s prism formula , which he later adopted VI is... 

Ladenburg admitted that Baeyer s experiments provided evidence against the prism formula, but still thought that it could apply in some cases. Baeyer later used Kekule s formula for phloroglucinol, saying that he was convinced that the behaviour of benzene in different compounds corresponds sometimes... 

The benzene molecule is a hybrid of Kekule and Dewar structures shown in B and C, Fig. 91. Since the molecule is planar, Ladenburg s prism formula is excluded. The Claus and the centric formulae (see p. 802) can be formed from the Kekule and Dewar structures and are not what are called canonical structures . ... 

Although these criticisms might seem to us to be very serious, to the chemists of the day the hexagonal structure for benzene solved so many problems that it was widely accepted. The reason for the equivalence of the carbon-carbon bonds and for the lack of reactivity remained matters for speculation, but the fundamental concept of the hexagonal ring encountered little opposition. The only serious alternative was the prism formula of Albert Ladenburg (1842-1911), but, while this... 

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