Question

Show the relative energy levels of the seven p molecular orbitals of the cycloheptatrienyl system. Tell which of the seven orbitals are filled in the cation, radical, and anion, and account for the aromaticity of the cycloheptatrienyl cation.

Short answer

Energy level diagram of cycloheptatrienyl cation, radical, and anion

Step-by-step solution

Energy level

The seven molecular orbitals are combined to give seven pi molecular orbitals, with a single lowest energy level orbital and degenerate pairs of the higher energy orbitals.

Cycloheptatrienyl cation, radical and anion

In the six pi-electron cations, there are two electrons in ${\mathrm{\psi }}_1$and also two electrons in ${\mathrm{\psi }}_2$and ${\mathrm{\psi }}_3$. Thus, the cation doesn’t have any partially filled orbitals, therefore, cycloheptatrienyl cation is aromatic.

In the remaining two cyclopheptatrienyl radical and cycloheptatrienyl anion, the pi electrons are occupied in the anti-bonding orbital also. So, these two systems are not aromatic compounds.

Energy level diagram of cycloheptatrienyl cation, radical, and anion