Question

What does the "circle" represent in the structural formula of benzene?

Short answer

Answer: The circle in the structural formula of benzene signifies the delocalized electrons shared across all six carbon atoms, which result in resonance and stability within the benzene molecule.

Step-by-step solution

Understand benzene's structure

Benzene is an organic compound with the molecular formula C6H6. It is a hexagonal ring of six carbon atoms, with each carbon atom bonded to one hydrogen atom. Its structural formula can be represented in different ways, including the Kekulé structure, which shows alternating single and double carbon-carbon bonds, and the resonance structure, which uses a circle to depict its unique bonding.

Kekulé structure of benzene

Benzene was initially thought to have a structure as proposed by Kekulé, which consists of alternating single and double carbon-carbon bonds. This structure also conveys the idea of resonance – that is, benzene can switch between two different representations with each double bond moving to a new position, resulting in equivalent structures. The actual structure of benzene, however, is an intermediate between these two resonance structures.

Delocalized electrons and resonance

The circle found in the structural formula of benzene represents the delocalization of electrons between the carbon atoms. The six electrons that would be found in three double bonds in a Kekulé structure are actually shared evenly across all six carbon atoms in the ring. These delocalized electrons create a very stable chemical structure, whereby each carbon-carbon bond is between a single and a double bond length. This phenomenon is known as resonance.

Interpret the circle in the benzene structural formula

The circle in the structural formula of benzene signifies the delocalized electrons shared across all six carbon atoms, which result in resonance and stability within the benzene molecule. This representation is a more accurate depiction of benzene's bonding and serves as an essential aspect of understanding its chemical properties.