Aromatic Heterocycles Practice Problems

Identify whether the following molecule is aromatic or not. If the molecule is aromatic, determine the value for n in Hückel's rule. If not, explain your answer using the rules of aromaticity.

Which of these compounds loses its aromaticity when protonated?

(i) The following two structures are isoelectronic. Explain.
(ii) What is the difference between the two structures?

Classify each of the following compounds as nonaromatic, antiaromatic, or aromatic. Provide a brief explanation for your answer.

Classify each of the following compounds as nonaromatic, antiaromatic, or aromatic. Provide a brief explanation for your answer.

Which of these heterocyclic compounds are aromatic? Explain your answer briefly.

The compounds listed below are not aromatic compounds. Provide the reaction needed to transform them into aromatic compounds.

Use resonance forms to illustrate the distribution of charge on the pyrrole derivative structure shown below.

Classify each of the following compounds as nonaromatic, antiaromatic, or aromatic. Provide a brief explanation for your answer.

The structure of p-triphenyl is illustrated below.

(i) Is it acceptable to classify p-triphenyl as a fused polynuclear aromatic hydrocarbon?

(ii) Count the number of pi electrons in p-triphenyl. How does this number compare to naphthalene's?

Shown below is the structure of p-triphenyl.

(i) If the heat of hydrogenation for p-triphenyl is 630 kJ/mol, and the heat of hydrogenation for an isolated alkene is 120 kJ/mol, determine the resonance energy of p-triphenyl.
(ii) Compare the resonance energy of p-triphenyl with that of three benzene rings and with that of naphthalene. Explain the difference in the resonance energies of p-triphenyl and naphthalene.
(The resonance energy of benzene and naphthalene is 150 kJ/mol and 252 kJ/mol, respectively.)

The compounds listed below are not aromatic compounds. Provide the reaction needed to transform them into aromatic compounds.

Identify the following heterocyclic compounds as aromatic or nonaromatic.