Friedrich August Kekulé von Stradonitz

His Name

Kekulé never used his first given name; he was known throughout his life as August Kekulé. After he was ennobled by the Kaiser in 1895, 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 Justus von Liebig he decided to study chemistry. Following his education in Giessen, he took postdoctoral fellowships in Paris (1851-52), in Chur, Switzerland (1852-53), and in London (1853-55), where he was decisively influenced by Alexander Williamson.

Theory of chemical structure

In 1856 Kekulé became Privatdozent at the University of Heidelberg. In 1858 he was hired as full professor at the University of Ghent, then in 1867 was called to Bonn, where he remained for the rest of his career. Basing his ideas on those of predecessors such as Williamson, Archibald Scott Couper independently arrived at the idea of self-linking of carbon atoms (his paper appeared in June 1858), 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. 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, 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 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 (1897) and the development of quantum mechanics (in the 1920s).

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 Joseph Loschmidt in 1861 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.

More evidence was available by 1865, especially regarding the relationships of aromatic 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 1865 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 1872 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 1928 by 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 1865 that in 1890 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 1886 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 1890 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 1890 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 1862.^[10] The other anecdote he told in 1890, 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. If true, this probably occurred in the late summer of 1855.^[11]

Honors

In 1895 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: Baeyer in 1905.

See also

• Non-Kekulé molecule
• Kekulé Program
• Auguste Laurent

References