Kekulé () zurück (Abb. 1). Heute wird die Kekuléformel als eine mesomere Grenzform (Abb. 2) aufgefasst, weil alle Bindungen im Benzolmolekül gleich lang. Der deutsche Chemiker August Kekulé von Stradonitz schlug dann eine Ringstruktur für das Benzol vor. Der Legende nach kam Kekulé dieser Einfall im. Kekulé drückte diesen Umstand der Mesomerie durch die zwei Strukturformeln aus, die jeweils nur einen Extrempunkt der Ladungswolke symbolisieren. Aufgrund.
August KekuleKekulé drückte diesen Umstand der Mesomerie durch die zwei Strukturformeln aus, die jeweils nur einen Extrempunkt der Ladungswolke symbolisieren. Aufgrund. Die wohl wichtigste Einzelentdeckung Kekulé war jedoch die Aufklärung der Benzolformel. Das Benzol war seit bekannt (entdeckt von. Kekulé: Benzol und die Geschichte der Struktursymbole. Authors; Authors and affiliations. Hans-Dieter Barke; Günther Harsch.
Kekule Benzol Tartalomjegyzék VideoCHEMISTRY AMAZING FACTS #1: KEKULE'S DREAM (OUROBOROS) vs BENZENE STRUCTURE
Benzene, however, caused a problem as with just 6 hydrogen atoms it was impossible to complete all the bonds formed by the carbon atoms unless there were a lot of very reactive double and triple bonds in the molecule.
Benzene is not very reactive so it was reasoned it could not have triple bonds in its molecules. Once again, according to his later memoirs, he fell into a doze in his Ghent study.
This time he saw chains of carbon atoms wriggling like snakes until one bit its own tail and formed a loop. When he awoke he realised that he had solved the problem.
The six carbon atoms of benzene were arranged in a hexagonal ring with a hydrogen atom attached to each carbon.
First he drew the structure using his sausages but then made other diagrams showing more clearly the hexagonal arrangement.
The structure contains three double bonds which should make benzene pretty reactive. In one of the first uses of X ray crystallography to determine a molecular structure, Kathleen Lonsdale at the Royal Institution proved that the six carbon atoms in the benzene ring were arranged in a planar flat , symmetrical hexagon.
Lonsdale was the first woman to become a Fellow of the Royal Society. In atomic force microscopy was used to make the atoms in benzene rings visible for the first time.
In diagrams of this sort, there is a carbon atom at each corner. You have to count the bonds leaving each carbon to work out how many hydrogens there are attached to it.
In this case, each carbon has three bonds leaving it. Because carbon atoms form four bonds, that means you are a bond missing - and that must be attached to a hydrogen atom.
Because of the three double bonds, you might expect benzene to have reactions like ethene - only more so!
Ethene undergoes addition reactions in which one of the two bonds joining the carbon atoms breaks, and the electrons are used to bond with additional atoms.
Benzene rarely does this. Instead, it usually undergoes substitution reactions in which one of the hydrogen atoms is replaced by something new. This article needs additional citations for verification.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Darmstadt , Grand Duchy of Hesse.
Bonn , German Empire. Random House Webster's Unabridged Dictionary. Organic Chemistry: The Name Game: Modern Coined Terms and Their Origins.
Cambridge University Press. Annalen der Chemie und Pharmacie. Couper Annales de chimie et de physique. Rocke University of Chicago Press.
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 an ancient symbol known as the ouroboros.
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.
If one takes the anecdote as reflecting an accurate memory of a real event, circumstances mentioned in the story suggest that it must have happened early in He told another autobiographical anecdote in the same speech, of an earlier vision of dancing atoms and molecules that led to his theory of structure, published in May This happened, he claimed, while he was riding on the upper deck of a horse-drawn omnibus in London.
If, for example, you hydrogenate ethene you get ethane:. In order to do a fair comparison with benzene a ring structure we're going to compare it with cyclohexene.
When hydrogen is added to this, cyclohexane, C 6 H 12 , is formed. The "CH" groups become CH 2 and the double bond is replaced by a single one.
In the cyclohexane case, for example, there is a carbon atom at each corner, and enough hydrogens to make the total bonds on each carbon atom up to four.
In this case, then, each corner represents CH 2. The hydrogenation equation could be written:. The enthalpy change during this reaction is kJ mol In other words, when 1 mole of cyclohexene reacts, kJ of heat energy is evolved.
The negative sign shows that heat is evolved.