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Benzene: Introduction to Aromatic Compounds

Structure of Benzene

Even though Michael Faraday had already discovered benzene and Eilhardt Mitscherlich had determined its empirical formula, the structure of benzene remained a riddle. Several possible structures were taken into account. Two of these structures were named after the scientists by whom they were proposed: Dewar benzene (after James Dewar) and Ladenburg benzene (after Albert Ladenburg). Two such other proposals for the benzene structure were benzvalene and 3,3'-bicyclopropenyl. The latter one was actually synthesized by W.E. Billups et al. in 1989.

Tab.1
Proposals of possible benzene structures
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The German chemist August Kekulé von Stradonitz then proposed a monocyclic structure of benzene, containing three cyclically conjugated double bonds. Systematically, this structure would be called 1,3,5-cyclohexatriene. As legend has it, Kekulé came up with the idea of this structure in a dream of snakes. Each of the snakes bit into the tail of another snake. As a result, the snakes depicted a cyclic structure.

Fig.9
Benzene structure illustrated by the so-called Kekulé formula.

Later, the so-called Kekulé formula was generally accepted. In 1861, even four years before Kekulé's proposal, the Austrian teacher Joseph Loschmidt had also published a similar benzene structure.

Fig.10
Kekulé formula.
Fig.11
Loschmidt's suggestion of benzene's structure.
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Exercises

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