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Kekulé, Friedrich August

carbon theory organic atoms

[kay kuhlay] (1829–96) German organic chemist; founder of structural organic chemistry, and proposer of ring structure for benzenoid compounds.

Kekulé began his student career in architecture at Giessen, but he heard give evidence in a murder trial and was attracted to his chemistry lectures. Later he studied in Paris and London. He claimed that the key idea of organic molecular structure came to him in a daydream, on the upper deck of a London bus. His theory (1858) adopted idea of valence; that each type of atom can combine with some fixed number of other atoms or groups. Kekulé proposed that this ‘valence’ for carbon atoms is four. He also proposed that carbon atoms could be linked together to form stable chains, which was a new and vital idea.

It only needed the further idea, gradually developed by many chemists, that these structural formulae based on carbon chains represented molecular reality, for organic chemical theory to make the largest step in its history: for these structure diagrams, as the formulae became, could be deduced from the chemical and physical properties of the compound. From the diagram, in turn, new properties could be predicted; and so these molecular structures became the fruitful focus of every organic chemist’s thinking. In the hands of especially, experimental work on this basis pushed ahead. The ideas of structural theory became well known through Kekulé’s lectures in Ghent (from 1858) and then at Bonn (from 1867) and from his textbook (1859).

Kekulé contributed little as an experimentalist, but his second gift to theory did much to form a basis for the new organic chemical industry making dyes and drugs from coal tar products. This was his proposal of 1865, that the six-carbon nucleus of benzene consisted of not a chain but a closed ring of carbon atoms. In benzene each carbon atom carries a hydrogen atom, but one or more of these can be replaced by other atoms or groups to give a vast range of compounds (see diagram). As with his structure theory, Kekulé was anticipated by in the idea of a cyclic molecule, but the latter’s illness ensured Kekulé’s superior place in developing the theory and securing his reputation.

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