Friedrich August Kekulé






German chemist Friedrich Kekulé, known for his work and theories in molecular structure, such as the tetravalent structure of carbon.
German chemist Friedrich Kekulé, known for his work and theories in molecular structure, such as the tetravalent structure of carbon.

GERMAN CHEMIST
1829–1896

Friedrich August Kekulé was born on September 7, 1829, in Darmstadt, Hesse (later part of Germany). He showed an early aptitude for both languages and drawing and wanted to be an architect. He began his architecture studies at the University of Geissen in 1847, but after attending the lectures of the famous chemist Justus von Liebig he switched to chemistry. Kekulé had great interest in the theoretical aspects of chemistry, and less in the more practical applications that so interested von Liebig. On von Liebig's advice Kekulé went to Paris in 1851 to further his chemical studies.

Paris during the 1850s was an ideal place for a young scientist, as there was a great deal of interest in that city in theoretical chemistry, particularly in the structure of molecules. Preexisting ideas (such as the dualism of Swedish chemist Jöns J. Berzelius) stressed that molecules formed because of the inherent electrical charges that individual elements possessed (which were sometimes opposing and therefore attractive). Organic molecules were not in keeping with the dualism concept, but some scientists proposed that they could be derived from a number of simple inorganic molecules.

Kekulé returned to Germany in 1852, obtained his doctoral degree at Geissen in that year, and then spent a year working in Switzerland. This was followed by two years in London (1853–1855), where he met the chemist Alexander Williamson. Williamson had extended Charles Gerhardt's "type theories" to explain how ethers could be derived from the water type. Kekulé, with Williamson's encouragement, extended type theory further and introduced a new type—the methane or marsh gas type. This led to the development of the tetravalent model of carbon and the understanding that carbon forms rings and chains.

Kekulé's principal insight was to realize that type theory did not take into account the specific combining power (or valences) of specific atoms. In 1857 Kekulé suggested that carbon was tetravalent, his suggestion based on the specific chemistries of the compounds that carbon formed with elements such as hydrogen (CH 4 ) and chlorine (CCl 4 ). Kekulé extended his ideas in the following year by suggesting that two carbon atoms bonded together in the formation of hydrocarbons such as ethane (C 2 H 6 ). Similarly, additional carbon and hydrogen units could be added, extending the carbon atom chain and forming an ordered series. A similar structural theory was developed independently at around the same time by the Scottish chemist Archibald Scott Couper, working in the laboratory of Adolphe Wurtz in Paris. Publication of Couper's paper was delayed by Wurtz (until Kekulé's had appeared) and the structural theory of organic chemistry is really a culmination of the efforts of Kekulé and Couper.

Kekulé was offered the position of professor of chemistry at the University of Ghent in Belgium in 1858. There his linguistic abilities stood him in good stead, as he had to lecture in French. In 1867 Kekulé was called to the University of Bonn and remained there until his death, on July 13, 1896.

In 1859 Kekulé started to use graphical representations of organic molecules, in part to emphasize the tetravalent nature of carbon atoms and their ability to form chains. He then turned his attention to the structure of benzene (C 6 H 6 ), a compound with unusual properties that could not be explained by any theories of the day.

Kekulé proposed in 1865 that benzene had a structure in which six carbon atoms formed a ring, with alternating single and double bonds. However, the chemistry of benzene was not always consistent with this structural formula. (All of the carbon atoms in a benzene molecule were equal and equivalent in terms of the reactions of benzene.) To overcome this problem, Kekulé suggested in 1872 that there were two forms of benzene, in dynamic equilibrium . Kekulé's dynamical theory proved to be only partially correct. In 1933 Linus Pauling used quantum mechanics to explain more fully the nature of benzene.

On March 11, 1890, on the occasion of the twenty-fifth anniversary of his announcement of his benzene theory, Kekulé gave a speech in Berlin in which he revealed that both his structural theories and the structure of benzene were revealed to him in dreams. Scholars have tended to dismiss his account of his own creative processes and have placed more stock in the early training that Kekulé received in architecture as the key to his inspiration.

JOSEF LOSCHMIDT (1821–1895)

Before Kekulé dreamed of his structure for benzene, Josef Loschmidt proposed the ring structure of the molecule. Unfortunately, Loschmidt did not publish his theory in a widely read scientific journal. As a result, the credit for this revolutionary theory is hotly debated today.

—Valerie Borek

SEE ALSO Berzelius, JÖns Jakob ; Liebig, Justus von ; Organic Chemistry ; Pauling, Linus .

Martin D. Saltzman

Bibliography

Gillis, Jean (1972). "Friedrich August Kekule." In The Dictionary of Scientific Biography, Volume 7. New York: Scribners.

Wotiz, John H. (1993). The Kekule Riddle: A Challenge for Chemists and Psychologists . Clearwater, FL: Cache River Press.



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