In 1865, August Kekule a German chemist proposed the structure of Benzene in a French paper. He suggested a hexagonal carbon ring with alternating single and double bonds between the carbon atoms. He later revised his theory in 1872, proposing that Benzene rapidly alternates between 2 structures, with single and double bonds changing positions.
Benzene's structure consists of a regular hexagon of 6 bonded carbon atoms, each with a hydrogen-bonded outside of the ring. The carbons are bonded to each other by a normal sigma bond but also by delocalised electrons above and below the ring. Because these electrons are delocalised the bond lengths in benzene are equal. This gives benzene unusual chemical properties as well as greater stability over its isomers, e.g. cyclohexene.
Benzene is a carcinogen. This is because it can be oxidised in the body to benzene oxide and this can interact with DNA in cells, leading to mutations which could alter important cellular processes. Moreover, Benzene is also an important and widely used industrial chemical involved in the manufacturing of varnishes, paints and gasoline; it is found in crude oil, which is an unrefined petroleum product.