18. Aromaticity

Draw a Frost circle for the cyclopropenyl anion and compare it to the Frost circle for the cyclopropenyl cation. What has changed?

Draw a Frost circle for the cyclopentadienyl cation and compare it to the Frost circle for the cyclopentadienyl anion. What has changed?

Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?

(b) 

Using a Frost circle, a student drew the molecular orbital picture shown for the cyclopentadienyl anion, determining it to be antiaromatic. Do you agree with this conclusion? Why or why not?

Following the instructions for drawing the energy levels of the molecular orbitals for the compounds shown in [Figure 8.17], draw the energy levels of the molecular orbitals for the cycloheptatrienyl cation. For each compound, show the distribution of the $\pi$ electrons. Which of the compounds are aromatic?

Following the instructions for drawing the energy levels of the molecular orbitals for the compounds shown in [Figure 8.17], draw the energy levels of the molecular orbitals for the cycloheptatrienyl cation. For each compound, show the distribution of the $\pi$ electrons. Which of the compounds are aromatic?

Following the instructions for drawing the energy levels of the molecular orbitals for the compounds shown in [Figure 8.17], draw the energy levels of the molecular orbitals for the cycloheptatrienyl cation. For each compound, show the distribution of the $\pi$ electrons. Which of the compounds are aromatic?

Draw the inscribed polygon for the following molecule.

The average C―C single bond length is 1.53 Å, and the average C=C double bond length is 1.31 Å. All of the C―C bonds in benzene are the same length (1.42 Å). Explain.

An incomplete Frost diagram for a seven-membered ring is shown. Include the necessary electrons to make it represent an aromatic molecule. Then the draw the structure to which it would correspond.

Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?

(a)

Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?

(c)