Contrasting Cases: Below the Surface

April 18, 2019
Teaching & LearningJulia Winter

I waded first into ChemEd research with Nicole Graulich’s review paper about organic chemistry understanding: The Tip the Iceberg in Organic Chemistry Classes: How do Students Deal with the Invisible? (Graulich, 2015). I was writing my very first NSF grant proposal in 2015 and I studied that paper, then submerged myself into the references cited in the paper, and then incorporated this educational research to justify the creation of new learning tools for organic chemistry. The metaphor of the iceberg from the paper was truly apt: research shows that students will focus on surface details (looking at structural differences, memorizing procedures) to get an answer. It’s only when a student grasps the interplay of energy, orbital structure, and dynamic processes (concepts that not directly observable from a chemical drawing) that a deeper understanding occurs.

We are currently at the end of the academic year. After two semesters of general chemistry and two more semesters of organic chemistry, we want our students to be swimming in the deep end! What are some tough problems that can be posed for students to check their understanding? These questions could be on the final exam, but ideally, students would have the opportunity to try out their conceptual deep diving skills prior to the exam. A straightforward method called Contrasting Cases, outlined in another Graulich paper, asks students to describe and discuss the reactivity between two to three similar structures (Graulich and Schween, 2018).

Below is an example of Contrasting Cases for ether-producing Sn2 reactions. The question posed to students would be to rank the reactions in terms of kinetics. Which would be fastest/slowest and explain why? For me (even after 20 years of teaching), this ranking was not readily apparent. I had to think! That’s what we want our students to do, too, correct? (BTW: The answers and explanations to the Contrasting Cases below are at this link. You are not in the shallow end anymore!)

The Graulich group not only gives great examples of these sets of Contrasting Case reactions (and even more in the supplemental material), they also propose a method for implementation in a class or lab discussion section. They called the process Compare – Predict – Observe – Explain, or CPOE cycle.  After listing similarities and differences, students would observe data, either through actual laboratory work or by being given results from a representative lab. They would then use these data to confirm or deny their predictions and give an explanation as to why this occurred.

The Contrasting Case example problems described in the paper serve as good exam reviews for students, especially as part of a group problem-solving session in an active learning curriculum.

Below are my favorite examples from the paper. Dive in!



The Tip of the Iceberg in Organic Chemistry Classes:How do Students deal with the Invisible?
Nicole Graulich
Chemistry Education Research and Practice. 2015, 16, 9–21.
Concept-Oriented Task Design: Making Purposeful Case Comparison in Organic Chemistry
Nicole Graulish and Michael Schween
Journal of Chemical Education 2018 95(3), 376-383.

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