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CHEM 216 Aromaticity

The Allegory of Zwischenstufe

In the early 1900s, chemists learned that, in some molecules, electrons are shared across multiple atoms and bonds. At the time, the German chemist Arndt referred to molecules with these delocalized electrons as “Zwischenstufe” (meaning hybrid structure)[1]. Today, we call them “resonance contributors”.[2] One limitation in using Lewis dot notation to depict resonance is that a single drawing does not adequately represent molecules with delocalized electrons. In this case, we use multiple Lewis structures with a double-headed arrow as shown below. Here, neither structure represents the actual aromatic molecule, which is a hybrid of the two.

This visual helps us understand the concept of resonance contributors in aromatic compounds. However, this is only one of many potential visualizations. An allegory is another way to envision difficult to understand concepts; it is a story that uses metaphor as a way to teach a principle. For example, Aesop’s fable of the Tortoise and Hare conveys the principle, “slow and steady wins the race” which teaches us to persevere in the face of adversity. As such, it uses common and identifiable characters and actions to help us understand a much more complex concept. Your objective is to write an allegorical story to teach a new organic chemistry student about electron delocalization in aromatic compounds. The story should aim to help the student understand and interpret drawings of resonance contributors, their limitations, and how the contributors relate to the actual form of the aromatic compound they represent.

Items to keep in mind:

  • This should be a story between 500–700 words.
  • All aromatic molecules can be described as having resonance, but not all molecules that have resonance are aromatic. Be sure to teach through your story what it means when a molecule is “aromatic”.
  • Although your primary goal is to teach the idea that no single resonance contributor represents the actual molecule, your allegorical story should also teach about the implications of resonance on molecular structure, chemical reactivity and the physical properties of aromatic compounds.
  • Readers of your story will play the role of a freshman student who is new to organic chemistry and who is trying to understand resonance for the first time. Therefore, you should think carefully about the use of metaphor, whether your metaphor accurately portrays the resonance phenomenon in aromatic compounds, and whether it will help the student to more easily understand it.
  • Because you are taking on the role of a teacher, carefully edit and proofread your essay to maintain credibility as an authority on aromaticity.
  • External references are not required, but if they are used they should be cited using MLA format.

[1] Arndt, F.; Scholz, E.; Nachtwey, P. Chem. Ber. 1924, 57, 1903-1911.

[2] Pauling, L.; Wheland, G.W. J. Chem. Phys. 1933, 1, 362-374.

Rubric

How did the author demonstrate his/her credibility as a teacher? Is the writing clear, direct, and concise? Is the story easy to follow? Are the transitions from one point of the story to the next smooth or abrupt? Is the grammar and spelling correct? Be specific—if these criteria aren’t met, in what ways can they be?

In what ways is the story written for an appropriate audience (freshman student)? How does its use of metaphor help students to understand more easily the resonance phenomenon in aromatic compounds? In what ways can it be more accessible?

Does the story conform to the all requirements of the assignment? Including: 1) length (500-700 words); 2) uses allegory to explain aromaticity; 3) addresses freshman audience; 4) establishes credibility through clear content and style; 5) MLA format for any external references? Be specific and thorough in your response.

In what ways does the story successfully teach what it means when a molecule is aromatic? Is the discussion of aromaticity clear, accurate, and complete? What relevant information from prior learning about aromaticity was included? What else should they include? How specifically might the story be improved? Be specific in your response.

In what ways does the story effectively use allegory to teach about the implications of resonance on molecular structure, chemical reactivity and the physical properties of aromatic compounds? How specifically might it be more effective?