18. Aromaticity

Draw a Frost circle for the cyclopropenyl anion and compare it to the Frost circle for the cyclopropenyl cation (Figure 23.22). What has changed?

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Draw a Frost circle for the cyclopentadienyl cation and compare it to the Frost circle for the cyclopentadienyl anion (Figure 23.22). What has changed?

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

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(••) 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?

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Following the instructions for drawing the energy levels of the molecular orbitals for the compounds <IMAGE>, draw the energy levels of the molecular orbitals for the cyclopropenyl cation. For each compound, show the distribution of the p electrons. Which of the compounds are aromatic?

Draw the inscribed polygon for the following molecule.