Cyclooctatetraene dianion, C8H8 2-, is an organic ion with the structure shown. Considering only the p bonds and not the s bonds, cyclooctatetraene dianion can be described by the following energy diagrams of its p molecular orbitals:
(d) Based on your MO energy diagram, is the dianion paramagnetic or diamagnetic?

Key Concepts

Molecular Orbitals (MOs)

Molecular orbitals are formed by the combination of atomic orbitals when atoms bond together. In the case of cyclooctatetraene dianion, the p orbitals combine to form bonding and antibonding molecular orbitals. The arrangement and occupancy of these MOs determine the electronic properties of the molecule, including its magnetic behavior.

Paramagnetism vs. Diamagnetism

Paramagnetism occurs in species that have unpaired electrons, leading to a net magnetic moment that can align with an external magnetic field. In contrast, diamagnetism is exhibited by species with all electrons paired, resulting in no net magnetic moment. The presence of unpaired electrons in the molecular orbitals of cyclooctatetraene dianion will dictate whether it is paramagnetic or diamagnetic.

Electron Configuration in MOs

The electron configuration in molecular orbitals is crucial for determining the magnetic properties of a molecule. Electrons fill the molecular orbitals starting from the lowest energy level, following the Pauli exclusion principle and Hund's rule. By analyzing the filling of the p molecular orbitals in cyclooctatetraene dianion, one can ascertain whether there are unpaired electrons, which would indicate paramagnetism.