August kekule biography

Friedrich August Kekule von Stradonitz (also August Kekulé) (September 7, – July 13, ) was a German organic chemist. One of the most prominent chemists in Europe from the s until his death, especially in the theoretical realm, he was the principal founder of the theory of chemical structure.

His Name

Kekulé never used his first given name; he was known throughout his life as August Kekulé.

Friedrich august kekule After graduating from secondary school, in he entered the University of Giessen , with the intention of studying architecture. After hearing the lectures of Justus von Liebig he decided to study chemistry. Following his education in Giessen , he took further doctorate fellowships in Paris , in Chur , Switzerland , and in London , where he was decisively influenced by Alexander Williamson. In , he was hired as a full professor at the University of Ghent. In , he was asked to work at the University of Bonn.

After he was ennobled by the Kaiser in , he adopted the name August Kekule von Stradonitz, without the French acute accent over the second "e". The French accent had apparently been added to the name by Kekulé's father during the Napoleonic occupation of Hesse by France, in order to ensure that French speakers pronounced the third syllable.

Early life

Kekulé was born in Darmstadt, the son of a civil servant. After graduating from secondary school, in he entered the University of Giessen, with the intention of studying architecture. After hearing the lectures of Justus von Liebig he decided to study chemistry. Following his education in Giessen, he took postdoctoral fellowships in Paris (), in Chur, Switzerland (), and in London (), where he was decisively influenced by Alexander Williamson.

Kekule von stradonitz friedrich august biography samples 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 , but after attending the lectures of the famous chemist Justus von Liebig he switched to chemistry. Paris during the s 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. 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.

Theory of chemical structure

In Kekulé became Privatdozent at the University of Heidelberg. In he was hired as full professor at the University of Ghent, then in was called to Bonn, where he remained for the rest of his career. Basing his ideas on those of predecessors such as Williamson, Edward Frankland, William Odling, Auguste Laurent, Charles Adolphe Wurtz and others, Kekulé was the principal formulator of the theory of chemical structure ().

This theory proceeds from the idea of atomic valence, especially the tetravalence of carbon (which Kekulé announced late in )^[1] and the ability of carbon atoms to link to each other (announced in a paper published in May )^[2], to the determination of the bonding order of all of the atoms in a molecule. Archibald Scott Couper independently arrived at the idea of self-linking of carbon atoms (his paper appeared in June ), and provided the first molecular formulas where lines symbolize bonds connecting the atoms.

For organic chemists, the theory of structure provided dramatic new clarity of understanding, and a reliable guide to both analytic and especially synthetic work.

Kekule structure of benzene

Kekulé benzene

August kekulé pronunciation

Story behind discovery of benzene structure

Kekulé meaning

As a consequence, the field of organic chemistry developed explosively from this point. Among those who were most active in pursuing early structural investigations were, in addition to Kekulé and Couper, Frankland, Wurtz, Alexander Crum Brown, Emil Erlenmeyer, and Aleksandr Mikhailovich Butlerov

Criticism

Kekulé's idea of assigning certain atoms to certain positions within the molecule, and schematically connecting them using what he called their "Verwandtschaftseinheiten" (affinity units, now called valences or bonds), was based largely on evidence from chemical reactions, rather than on instrumental methods that could peer directly into the molecule, such as X-ray crystallography.

Such physical methods of structural determination had not yet been developed, so chemists of Kekulé's day had to rely almost entirely on so-called "wet" chemistry. Some chemists, notably Adolph Wilhelm Hermann Kolbe, heavily criticized the use of structural formulas that were offered, as he thought, without proof. However, most chemists followed Kekulé's lead in pursuing and developing what some have called "classical" structure theory, which was modified after the discovery of electrons () and the development of quantum mechanics (in the s).

Friedrich august von hayek

Kekule von stradonitz friedrich august biography samples images

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The idea that the number of valences of a given element was invariant was a key component of Kekulé's version of structural chemistry. This generalization suffered from many exceptions, and was subsequently replaced by the suggestion that valences were fixed at certain oxidation states. For example, periodic acid according to Kekuléan structure theory could be represented by the chain structure I-O-O-O-O-H.

By contrast, the modern structure of (meta) periodic acid has all four oxygen atoms surrounding the iodine in a tetrahedral geometry.

Benzene

Kekulé's most famous work was on the structure of benzene. In Kekulé published a paper in French (for he was then still in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds.^[3] The next year he published a much longer paper in German on the same subject.^[4] The empirical formula for benzene had been long known, but its highly unsaturated structure was challenging to determine.

Archibald Scott Couper in and Joseph Loschmidt in suggested possible structures that contained multiple double bonds or multiple rings, but the study of aromatic compounds was in its earliest years, and too little evidence was then available to help chemists decide on any particular structure.

Friedrich august von hayek: Friedrich August Kekulé, later Friedrich August Kekule von Stradonitz (/ ˈ k eɪ k əl eɪ / KAY-kə-lay, [1] German: [ˈfʁiːdʁɪç ˈʔaʊɡʊst ˈkeːkuleː fɔn ʃtʁaˈdoːnɪts]; 7 September – 13 July ), was a German organic chemist.

More evidence was available by , especially regarding the relationships of aromatic isomers. Kekulé argued for his proposed structure by considering the number of isomers observed for derivatives of benzene. For every monoderivative of benzene (C₆H₅X, where X = Cl, OH, CH₃, NH₂, etc.) only one isomer was ever found, implying that all six carbons are equivalent, so that substitution on any carbon gives only a single possible product.

For diderivatives such as the toluidines, C₆H₄(NH₂)(CH₃), three isomers were observed, for which Kekulé proposed structures with the two substituted carbon atoms separated by one, two and three carbon-carbon bonds, later named ortho, meta and para isomers respectively.

The counting of possible isomers for diderivatives was however criticized by Albert Ladenburg, a former student of Kekulé, who argued that Kekulé's structure implied two distinct "ortho" structures, depending on whether the substituted carbons are separated by a single or a double bond. Since ortho derivatives of benzene were never actually found in more than one isomeric form, Kekulé modified his proposal in and suggested that the benzene molecule oscillates between two equivalent structures, in such a way that the single and double bonds continually interchange positions.

^[5] This implies that all six carbon-carbon bonds are equivalent, as each is single half the time and double half the time. A firmer theoretical basis for a similar idea was later proposed in by Linus Pauling, who replaced Kekulé's oscillation by the concept of resonance between quantum-mechanical structures.

The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry after that in the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory.

He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the Ouroboros). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. It is curious that a similar humorous depiction of benzene had appeared in in the Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.^[6] Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well-known through oral transmission even if it had not yet appeared in print.^[7] Others have speculated that Kekulé's story in was a re-parody of the monkey spoof, and was a mere invention rather than a recollection of an event in his life.

Kekulé's speech^[8] in which these anecdotes appeared has been translated into English.^[9] If one takes the anecdote as the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in ^[10] The other anecdote he told in , of a vision of dancing atoms and molecules that led to his theory of structure, happened (he said) while he was riding on the upper deck of a horse-drawn omnibus in London.

Kekule von stradonitz friedrich august biography samples pdf

Kekule originally studied architecture, but later became interested in chemistry. He was an assistant to J. Stenhouse at St. From he was Privadozent Lecturer in Heidelberg, and was a professor at Ghent in and Bonn in He postulated that carbon atoms can combine with one another to form chains of any length and complexity, the valency of carbon is always four, and the study of reaction products can give information about structure.

If true, this probably occurred in the late summer of ^[11]

Honors

In Kekulé was ennobled by Kaiser Wilhelm II of Germany, giving him the right to add "von Stradonitz" to his name, referring to a possession of his patrilineal ancestors in Stradonice, Bohemia. Of the first five Nobel Prizes in Chemistry, his students won three: van 't Hoff in , Fischer in and Baeyer in

See also

 

References