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Benzene Ring

Benzene belongs to the family of aromatic compounds with a ring structure. It is the simplest aromatic hydrocarbon consisting of six carbon atoms bonded with alternative single and double bonds. Each of the carbon atoms is singly bonded to a hydrogen atom. The six conjugate carbon atoms and p-orbital delocalization due to sp2 hybridization give rise to a resonance structure [1-4].

Benzene is a colorless liquid with a distinct odor. Its boiling point is 80.1 ˚C. English scientist Michael Faraday discovered it in 1825 from the oily residue left by producing illuminating gas. German organic chemist Friedrich August Kekulé published a paper on its structure in 1865.

Characteristics [1-3]

  • A planar molecule with six carbon atoms arranged in a hexagon
  • Each carbon atom shares a single bond with a hydrogen atom, giving rise to the chemical formula C6H6
  • Carbon atoms alternatively share single and double bonds and hence, have a bond length somewhere between single and double bonds
  • Delocalized pi electrons are present above and below the plane of the ring
  • Benzene cannot participate in addition reaction since adding compounds would break the ring, and benzene would lose its stability

Structure

Benzene has a molecular formula, C6H6, whose structure is shown below. There are three ways to illustrate its structure [1-3].

As shown in illustration (1) below, benzene has six carbon atoms arranged in a ring. Single and double bonds alternately separate the carbon atoms. This kind of atomic arrangement is known as a conjugated structure. Each carbon atom is singly bonded with a hydrogen atom. This structure is also known as the Lewis dot structure of benzene.

Another way of representing benzene is the illustration (2). Here, we see a hexagon with each edge representing one carbon atom. The three double bonds are also shown. However, the hydrogen atoms are not shown.

Illustration (3) represents a hexagon with a circle inside. The circle represents the delocalized pi electrons. The structural formula of benzene is often represented by this structure.

Benzene Ring

Bond Length and Bond Angle

The C-C bond length in benzene is 1.39 Å, and each bond angle is 120 ˚. The bond length value is between the C-C single bond (1.47 Å) and the C≡C triple bond (1.34 Å). The pi electron delocalization makes the bond count as one and a half bond between the carbon atoms. Moreover, experiments have shown that benzene’s bond length is between single and double bond values [1].

FAQs

Q.1. How many degrees of unsaturation is a benzene ring?

Ans. There are four degrees of unsaturation in a benzene ring.

Q.2. How did Kekulé discover the structure of benzene?

Ans. Kekulé pictured benzene’s ring structure after dreaming of a snake eating its tail.

References

  1. Chem.libretexts.org
  2. Ionscience.com
  3. Study.com
  4. Chem.ucla.edu

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