Friedrich August Kekule

Friedrich August Kekule

Organic chemistry – the chemistry of the carbon compounds – has been established as a definite branch of chemistry within the last hundred years.  Although several other famous chemists before him had been interested in organic chemistry, Friedrich August Kekule played an important role in its development. His principle contributions were concerned with the structures (the molecular architecture) of organic compounds.

At the beginning of the nineteenth century, organic and inorganic chemistry were regarded as two almost unrelated sciences. It was thought that some “vital principle” was concerned in the formation  of the complicated (organic) substances found in animals and plants. And even after two organic compounds (ethyl alcohol and urea) had been prepared artificially from non-living (inorganic) matter, these old ideas were slow to die.

By the middle of the century quite a large number of organic substances had been isolated, and attempts had been made to find the chemical composition of many of them. At first chemists were satisfied when they had found the proportions by weight of the various elements in a compound.Later they tried to work out the number of atoms of the various elements present in each molecule. As there was still some uncertainty over the atomic weights of even the common elements, several different formulae often existed for the same compound. In 1861 Friedrich August Kekule recorded nineteen formulae for acetic acid.

At the time he idea of valency was in its infancy, but Friedrich August Kekule managed to prove that carbon had a valency of four. One atom of carbon combines with four atoms of a monovalent elementlike hydrogen (as in methane) or two atoms of a divalent element like oxygen (as in carbon dioxide). Friedrich August Kekule also explained the formula of ethylene (C2H4) and similar compounds. He showed that if double valency bonds hold the two carbon atoms in ethylene together, the four-valent nature of carbon is preserved.

Of almost equal importance was Friedrich August Kekule’s discovery of the ring formula for benzene (C6H6). For some time he had been puzzling over its structure. Until then it had been assumed that all organic compounds had an open chain of carbon atoms as a backbone. Then, while dozing in his study, he had a vision of chains of carbon atoms twisting and curling like serpents; suddenly one gripped its own tail to make the closed ring. This showed that  carbon atoms did not have to be arranged in open chains. In fact, a ring structure for benzene accounted for several of its properties.

Friedrich August Kekule was born as Darmstadt in Germany in 1829. In 1847 he entered the University of Guissen to study architecture, but under the influence of Justus von Liebig, another native of Darmstadt, Friedrich August Kekule turned his attention to chemistry. After studying in Paris under Jean Baptise Dumas, he became a Professor of Chemistry at Ghent in 1858 and in Bonn in 1865. He died in 1896.