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Arenes and Aromaticity Questions
Qu 1 Use the following list of compounds to answer the questions below:

Select the compound that is best described as: 

(a) A neutral, 4 p-electron, anti-aromatic system.

(b) A 6 p-electron, aromatic system.

(c) An aromatic system because n=2 in the Huckel 4n+2 rule.

(d) A non-aromatic, conjugated 6 p-electron system

(e) A non conjugated hydrocarbon.

(f) Non-aromatic as drawn, but if H- were removed would give an aromatic cation.

(g) Non-aromatic as drawn, but has an important resonance structure that is aromatic.

(h) Non-aromatic as drawn but has an aromatic conjugate base.

Qu 2: Consider the pKa data for the following aromatic N containing systems:

Henderson-Hasselbach equation:      pKa = pH + log ([A-]/[HA])

Based on the scheme provided,

(a) Which species is the strongest acid ?

(b) At pH=4.2, what is the relative ratio of pyridine to its conjugate acid ?

(c) Which is the better base:  pyridine or aniline, and why ?

(d) Why is pyrrole is a weaker base than pyridine?

Qu 3: Rate the resonance energies (in comparison to one another) of each of the following:

Qu 4: Rate the relative stability of the following carbocations (in comparison to one another):

Qu 5: Use the following data to answer the questions below:

(a) Calculate the resonance energy of anthracene, 

(b) Anthracene is known to react with maleic anhydride in a Diels-Alder reaction. Predict which of the products shown  is obtained. Why ? 

Answers ?

organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary