Aromatic hydrocarbons have a cyclic structure.The first representative of this series - the benzene (C6H6).The formula that reflects the structure of matter was first proposed by the chemist Kekule in 1865.According to the stories of the scientist, he had long pondered the mystery of benzene.One night he had a snake bites its own tail.On the morning of the structural formula of benzene has been drawn up.It was a ring of 6 carbon atoms.Three of them were at the double bond.
structure of benzene
carbon in aromatic hydrocarbons form a regular hexagon.Sometimes when writing reaction equations represent its elongated in the vertical direction.This group of atoms has a special name - the benzene ring.Confirmation of cyclic structure of benzene is its receipt of three molecules of acetylene - unsaturated hydrocarbons with a triple bond.Aromatic hydrocarbons are unsaturated and also exhibit some of the properties that are typical of alkenes.For this reason, in the benzene ring three dashes extending parallel faces, note the presence of a double bond.This formula of benzene does not fully reflect the state of the carbon atoms in the molecule.
Benzene: A formula that reflects the true structure
In reality, the relationship between the carbon equivalent in the ring together.Among them was unable to allocate single and double.This feature is explained by the electronic structure of benzene, which is located in the nucleus of the carbon in the sp2-hybridisation, coupled with its neighbors in the ring and three conventional hydrogen single bonds.In this case a hexagon, which are in the same plane 6 carbon atoms and 6 - hydrogen.Only the electron clouds of the fourth p-electrons is not involved in the hybridization, arranged differently.Their shape resembles a dumbbell, the center falls on the plane of the ring.A thickened portion located above and below.In this case, on a benzene ring, and below it are two electron densities encountered in overlapping clouds of p-electrons.There is a general chemical bond to a carbon in the ring.
Properties benzene ring
Due total electron density reduces the distance between the carbon in the ring.They are equal to 0.14 nm.If in the nucleus of benzene there were single and double bonds, it would be two indicators: 0.134 and 0.154 nm.True benzene structural formula should not contain single and double bonds.Therefore, aromatic hydrocarbons is referred to unsaturated organic compounds only formally.In composition they resemble alkenes, but may come in a substitution reaction, which is characteristic of saturated hydrocarbons.The aromatic nucleus of benzene has considerable resistance to oxidants.All these features suggest a special type of ring connection - not a double and a single.
How to portray the formula of benzene?
The correct formula of the benzene with three double bonds as in Kekule, but in the form of a hexagon with a circle inside.It symbolizes total membership 6 electrons.
finds confirmation in the symmetry of the structure and properties of matter.Benzene ring is stable, has significant energy coupling.The properties of the first representative of aromatic hydrocarbons occur in its homologues.Each of them can be represented as a derivative in which the replacement of hydrogen on different hydrocarbon radicals.
