Formula of benzene: which of the variations is correct?

Aromatic hydrocarbons have a cyclic structure. The first representative of this series is benzene (C ₆ H ₆ ). A formula reflecting the structure of matter was first proposed by the chemist Kekule in 1865. According to the scientist, he pondered the riddle of benzene for a long time. One night he dreamed of a snake biting his tail. In the morning, the structural formula of benzene was already compiled. It was a ring of 6 carbon atoms. Three of them were with a double connection.

The structure of benzene

Carbon in the composition of aromatic hydrocarbons forms a regular hexagon. Sometimes when recording the reaction equations, it is drawn out in a vertical direction. This group of atoms has received a special name - a benzene nucleus. A confirmation of the cyclic structure of benzene is its production from three molecules of acetylene - an unsaturated hydrocarbon with a triple bond. Aromatic hydrocarbons are also unsaturated and exhibit some properties characteristic of alkenes. For this reason, in the benzene ring, three dashes running parallel to the faces indicate the presence of a double bond. This formula of benzene does not fully reflect the state of carbon atoms in the molecule.

Benzene: a formula that reflects the true structure

In reality, the bonds between the carbon in the ring are equivalent to each other. Among them, it was not possible to single out single and double. This feature is explained by the electronic structure of benzene, in which the carbon in the nucleus is in the sp ² -hybridized state, is connected to the neighbors along the ring and hydrogen by three ordinary single bonds. In this case, a hexagon appears in which 6 carbon atoms and 6 hydrogen atoms are in one plane. Only the electron clouds of the fourth p-electrons not participating in the hybridization are arranged differently. Their shape resembles dumbbells, the center falls on the plane of the ring. And the thickened parts are on top and bottom. In this case, above the benzene nucleus and below it, there are two electron densities that appeared when overlapping clouds of p-electrons. There is a general chemical bond for carbon in the ring.

Properties of the benzene ring

Due to the total electron density, the distances between the carbon in the ring are reduced. They are equal to 0.14 nm. If there were single and double bonds in the benzene core, there would be two indicators: 0.134 and 0.154 nm. The true structural formula of benzene should not contain simple and double bonds. Therefore, aromatic hydrocarbons are classified as unsaturated organic compounds only formally. In composition, they resemble alkenes, but they can enter substitution reactions, which is typical for the ultimate hydrocarbons. The aromatic core of benzene has considerable resistance to oxidants. All these features allow us to consider the ring a special type of connection - not double and not single.

How to represent the formula of benzene?

Correct is the formula of benzene not with three double bonds, as in Kekul, but in the form of a hexagon with a circle inside. It symbolizes the common affiliation of the six electrons.

The symmetry of the structure is also confirmed in the properties of matter. The benzene ring is stable, has a significant conjugation energy. The properties of the first representative of aromatic hydrocarbons are manifested in his homologues. Each of them can be represented as a derivative in which hydrogen is substituted for various hydrocarbon radicals.