Hydrocarbons, like benzene, are organic compounds consisting of only carbon and hydrogen. Most hydrocarbons that occur naturally on Earth can be found in crude oil which is a result of large amounts of ancient organic matter decomposing under the surface of the Earth over millions of years. This organic matter, consisting of dead plants and animals, was buried over time and released large amounts of both carbon and hydrogen as it decayed. This provided the chemical building blocks that later rearranged themselves into crude oil and the array of hydrocarbons it contains today.
Benzene, the simplest of the hydrocarbons, is an organic chemical compound consisting of six carbon atoms and six hydrogen atoms. Each set of six carbon atoms are arranged in a ring with one hydrogen atom bonded to each carbon atom outside the carbon ring. This basic structure, identified in 1865 by German scientist, Friedrich August Kekulé, is the primary building block of all hydrocarbons and is known to chemists as the benzene ring.
Because aromatic hydrocarbons don’t quickly react with other compounds or easily break apart, they are considered extremely stable. For the most part, their stability is a result of the nature of the covalent bonds between neighboring carbon atoms and each carbon atoms’ bond with its corresponding hydrogen atom. An aromatic hydrocarbon, like benzene, is characterized by this ring-like structure and usually considered to consist of a pattern of alternating single and double bonds. However, to truly understand the stability of the benzene ring, a closer examination of those bonds is necessary.
The bond between neighboring carbon atoms in a benzene ring is known as a pi bond, meaning that parallel p-orbitals of any two neighboring carbon atoms in a benzene ring overlap side-to-side, creating a perpendicular plane to their nuclei. What makes the pi bonds of a benzene ring even more stable is that all six carbon atoms share delocalized pi electrons. These delocalized electrons strengthen the entire ring of carbon atoms.
Each individual carbon atom in a benzene ring is also sigma bonded to a single hydrogen atom. Sigma bonds are the strongest possible covalent bonds and are created by a direct overlap between s-orbitals or a single lobe of p-orbitals.
The stability of these bonds in benzene and other hydrocarbons is what makes them so useful in industrial chemical production.