Ladenburg benzene formula

This structure accounts for the fact that benzene has only one monosubstitution product and three isomeric disubstitution products. However, Ladenburg s formula is not able to solve the problem of there being only one 1,2-dimethyl-benzene. According to this formula, there would be two possible isomers for this compound ... 

Bicyclo[2.2.0]hexadienes and prismanes are valence isomers of benzenes. These compiounds actually have the structures that were proposed for benzenes in the nineteenth century. Prismanes have the Ladenburg formula, and bicyclo[2.2.0]-hexadienes have the Dewar formula. Because of this bicyclo[2.2.0]hexadiene is often called Dewar benzene. On page 32 it was mentioned that Dewar formulas are canonical forms (though not very important) of benzenes. Yet, they also exist as separate compounds in which the positions of the nuclei are different from those of benzenes. 

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,... 

Exercise 1-6 The German chemist Ladenburg, in 1868, suggested the prismatic formula 17 for benzene ... 

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. 

In the course of the study of the structure of benzene, several structural formulas have been proposed for it. Well known structures are Kekule s cyclohexatriene, Ladenburg s prismane, Thiele s partial bond structure, and Dewar s bicyclohexadiene. Later, Huckel proposed benzvalene as another structure of benzene. Since Kekule s structure was gradually accepted as the structure of benzene, other structures are only of historical importance. 

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. 

Ladenburg, partly in collaboration with Friedel, published researches on inorganic (silicon chloroform, silicon-oxalic acid Si2H204, silicon oxychloride, etc.), and organic (aliphatic and aromatic) compounds of silicon. He established the formula Su2(C2H5)g for tin triethyP discovered by Cahours (see p. 511), and prepared other organic tin compounds. He proved that mesity-lene is symmetrical trimethylbenzene. His work on the structure of benzene is considered elsewhere (p. 802). 

Ladenburg criticised Kekule s formula on the ground that two different ortho-compounds should be obtainable. He showed that only three disubstitution products and only one pentachlorobenzene exist. In an elaborate experimental investigation he proved that all six hydrogen atoms in benzene are equivalent. In his first paper in 1869 he proved that all the carbon atoms are joined by single linkages, giving three formulae (see p. 803). 

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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