Atomic compounds, August Kekule

Asymmetrical metal atoms, 293 Atomic compounds, August Kekule s definition, 5... 

From the concept of isomerism we can trace the origins of the structural theory—the idea that a precise arrangement of atoms uniquely defines a substance Ammonium cyanate and urea are different compounds because they have different structures To some degree the structural theory was an idea whose time had come Three scientists stand out however for independently proposing the elements of the structural theory August Kekule Archibald S Couper and Alexander M Butlerov... 

By the mid-1800s, the new science of chemistry was developing rapidly and chemists had begun to probe the forces holding compounds together. In 1858, August Kekule and Archibald Couper independently proposed that, in all its compounds, carbon is tetravalent—it always forms four bonds when it joins other elements to form stable compounds. Furthermore, said Kekule, carbon atoms can bond to one another to form extended chains of linked atoms. 

The chemical structure of benzene remained one of the great mysteries in chemistry for nearly half a century. The compound s formula, C6H6, suggests that it contains three double bonds. A double bond consists of four electrons that hold two atoms in close proximity to each other in a molecule. Yet benzene has none of the chemical properties common to double-bonded substances. The solution to this problem was suggested in 1865 by the German chemist Friedrich August Kekule (1829-1896). Kekule suggested that the six... 

In 1865, August Kekule postulated the ring formula for benzene in a publication entitled Investigations into aromatic compounds , which he summarized in the sentence These facts clearly lead to the conclusion that in all aromatic substances one and the same atomic group or, if one prefers, a common core can be found, which consists of six carbon atoms . 

Benzene (CeHg), the parent compound of the aromatic hydrocarbons, was discovered by Michael Faraday in 1826. Over the next 40 years, chemists were preoccupied with determining its molecular structure. Despite the small number of atoms in the molecule, there are quite a few ways to represent the structure of benzene without violating the tetravalency of carbon. Most of the proposed structures were rejected, however, because they did not explain the known properties of benzene. Finally, in 1865, August Kekule deduced that the benzene molecule could be best represented by a ring structure—a cyclic compound consisting of six carbon atoms ... 

Figure 2.5 Artist s depiction of Friedrich August von Kekule s dream of a snake eating its own taii, a dream that aided von Kekule in soivingthe probiem of the structure for the organic compound benzene, composed of a ring of carbon atoms.

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