Question

Bcnzyne contain c1ccccc1 (1) Six-sp \(^{2}\) hybridised \(C\) -atoms (2) Four-sp \(^{2}\) hybridised and two sp-hybridised C-atoms (3) Two-sp \(^{2}\) hybridised and four sp-hybridised C-atoms (4) None of these

Short answer

Six \( sp^2 \) hybridized carbon atoms.

Step-by-step solution

Understand the benzene structure

Benzene is represented by the molecular formula \( \text{C}_6\text{H}_6 \). Its structure consists of a six-carbon ring with alternating double bonds. This aromatic ring is planar and all carbon atoms are \( sp^2 \) hybridized.

Analyze the hybridization

In benzene, each carbon atom forms one \( \text{C-C} \) single bond and one \( \text{C-H} \) bond and participates in one \( \text{C=C} \) double bond. These bonds require \( sp^2 \) hybridization. Therefore, all six carbon atoms are \( sp^2 \) hybridized.

Conclusion

Based on the above analysis, benzene contains six \( sp^2 \) hybridized carbon atoms.

Key concepts

sp2 Hybridization

In chemistry, hybridization describes the mixing of atomic orbitals to form new hybrid orbitals. These hybrid orbitals help in forming covalent bonds. For benzene, each carbon atom undergoes sp2 hybridization. This occurs because each carbon atom needs three equivalent orbitals to form sigma bonds.
sp2 hybridization results in three sp2 hybrid orbitals lying in a plane, 120 degrees apart.
In benzene, every carbon atom forms one C-C sigma bond and one C-H sigma bond through these hybrid orbitals. The unhybridized p orbital at each carbon atom participates in the C=C pi bonds. These pi bonds lead to a ring of electron density above and below the plane, contributing to benzene's stability. This delocalization of electrons explains benzene's characteristic aromaticity.

Aromatic Compounds

Aromatic compounds like benzene have unique stability and special properties. This stability arises from the delocalized pi electrons in the ring structure. For a compound to be aromatic, it needs to satisfy Hückel's rule: having 4n+2 pi electrons, where n is a non-negative integer.
Benzene, with six pi electrons (n=1), meets this requirement. The planar structure and resonance in benzene permit the delocalization of these electrons throughout the ring, leading to a lower energy state and significant stability. Benzene's ring is often represented with a circle inside, symbolizing the delocalized electrons. This resonance gives rise to benzene's characteristic reactions, typically substitutions rather than additions, preserving the aromatic system.

Molecular Structure

The molecular structure of benzene is a perfect hexagon. Each carbon atom in benzene is bonded to two other carbon atoms and one hydrogen atom. This results in a planar, cyclic structure with alternating double bonds, a hallmark of aromatic compounds.
The bond lengths in benzene are equal, about 1.39 Å, which is an intermediate length between single and double bonds. This equal bond length results from the resonance structures where the electrons are shared equally among all six C-C bonds. These observations were confirmed by X-ray diffraction studies.
The hexagonal symmetry and the equivalent bond lengths in benzene contribute to its unique properties, such as its reluctance to participate in reactions that would disrupt this stable structure.