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.

Identify the following heterocyclic compounds as aromatic or nonaromatic.

Identify the basic and non-basic nitrogen atoms in adenine. Explain why the non-basic nitrogen atom is not easily protonated.

Classify each of the given species as aromatic, antiaromatic, or nonaromatic. For those classified as aromatic or antiaromatic, specify the number of delocalized π electrons in the cyclic system.

Dianions of hydrocarbons are exceedingly rare. For the given reaction:

A hydrocarbon (2,3,4,6-tetramethyl-1,5-dihydropentalene) reacts with 2 equivalents C₃H₇Li to form a dianion with a molecular formula of [C₁₂H₁₄]^2-. Draw the plausible structure of the dianion formed and explain the reason for it forming readily.

Which compounds are likely to be aromatic? Explain why they are aromatic.

Nucleotides are the building blocks of DNA, which is composed of deoxyribose (a sugar) and four heterocyclic bases. These bases are adenine, guanine, cytosine, and thymine. Adenine and guanine are purines while cytosine and thymine are pyrimidines. Can any of these bases form tautomers that exhibit aromaticity?

A chemist has synthesized and aims to study the following compound:

(i) Is the compound aromatic, antiaromatic or nonaromatic?

(ii) Provide a possible reason why this molecule is synthesized with three tert-butyl substituents as opposed to an unsubstituted compound.

Classify each species as aromatic, antiaromatic, or nonaromatic. Provide the number of π electrons in the ring for the aromatic and antiaromatic species.

Classify each species as aromatic, antiaromatic, or nonaromatic. Give the number of π electrons in the ring for the aromatic and antiaromatic species.

The following compound seems like an unlikely candidate for exhibiting optical activity as all its atoms are sp² hybridized and should theoretically lie flat. However, the compound does display chirality and has been found to have an extremely high optical activity. Explain why the compound is optically active and has a high degree of specific rotation.