Benzene C6H6 is an organic compound with a planar hexagonal ring structure, where each carbon atom is bonded to two other carbon atoms and one hydrogen atom. The electronic structure and molecular geometry of benzene can be understood using concepts from molecular orbital theory, valence bond theory, and quantum chemical calculations.Electronic Structure:Benzene has a conjugated system of alternating single and double bonds between the carbon atoms, which can also be represented as a resonance hybrid of two Kekulé structures. In reality, the electrons in the double bonds are delocalized over the entire ring, creating a stable aromatic system. This delocalization can be described by molecular orbital theory, where the six -electrons occupy three bonding molecular orbitals MOs that are formed by the linear combination of the 2p orbitals on each carbon atom.Molecular Geometry:The molecular geometry of benzene is planar and hexagonal. Each carbon atom is sp2 hybridized, forming three sigma bonds with bond angles of approximately 120 degrees. The remaining unhybridized 2p orbital on each carbon atom is perpendicular to the plane of the ring and participates in the delocalized -bonding system.Quantum Chemical Calculations:To determine the electronic structure and molecular geometry of benzene using quantum chemical calculations, one can employ methods such as Hartree-Fock HF or Density Functional Theory DFT . These methods solve the Schrödinger equation for the molecule, providing information about the molecular orbitals, electron densities, and energy levels.1. Choose a suitable basis set, which is a mathematical representation of the atomic orbitals used in the calculations.2. Perform a geometry optimization to find the lowest energy conformation of the molecule. This will provide the equilibrium bond lengths and angles, confirming the planar hexagonal structure of benzene.3. Calculate the molecular orbitals and their corresponding energies using the chosen method HF or DFT . This will provide information about the delocalized -bonding system and the distribution of electrons in the molecule.4. Analyze the results to understand the electronic structure and molecular geometry of benzene. Visualization tools can be used to display the molecular orbitals, electron densities, and other properties of interest.In summary, benzene has a planar hexagonal molecular geometry with a delocalized -bonding system. Quantum chemical calculations, such as Hartree-Fock or Density Functional Theory, can be used to determine the electronic structure and molecular geometry of benzene by solving the Schrödinger equation and analyzing the resulting molecular orbitals and electron densities.