Chapter 14, Problem 14.36P

Interpretation Introduction

Interpretation:

The $\text{π}$ MO energy diagram for $\left[\text{10}\right]\text{annulene}$ is to be drawn similar to those in Figures 14-19 and 14-21. The orbitals are to be filled up with the appropriate number of $\text{π}$ electrons. Whether $\left[\text{10}\right]\text{annulene}$ is aromatic or antiaromatic is to be determined.

Concept introduction:

The relative energies of fully conjugated, cyclic $\text{π}$ MOs can be derived using Frost method. The steps involved Frost method are as follows:

• The polygon representing the line structure of cyclic compound is drawn by pointing one of the vertices directly downward.
• The horizontal dashed line is drawn through the center of polygon.
• A short horizontal solid line is drawn at each vertices and the $\text{π}$ electrons are distributed among them, indicates the energies of $\text{π}$ MOs.
• The distribution of $\text{π}$ electrons started from the lowest energy $\text{π}$ MO and continued to highest energy $\text{π}$ MO.
• According to the Hund’s rule each MO is occupied by two electrons with opposite spin before moving to higher energy MO.

The short solid lines below the central dashed line represent the bonding $\text{π}$ MOs, those above the central dashed line represents the antibonding $\text{π}$ MOs and those right on the central dashed line are represents the nonbonding $\text{π}$ MOs. If the bonding $\text{π}$ MOs are completely filled, each with two electrons while the antibonding and nonbonding $\text{π}$ MOs are empty then the molecule is said to be an aromatic.