Mechanistic reasoning: Finding the path

November 28, 2018
Teaching & LearningSarah Wegwerth

“Success is a journey, not a destination. The doing is often more important than the outcome.” -Arthur Ashe

When I joined Alchemie, the Mechanisms app had already been released with the first sixty puzzles. Of course, I immediately fell in love with the product and its design -- I did agree to become a member of the team!

One thing about the app was perplexing: why the task cards, the images that show the reaction pieces at the beginning of the puzzles, were not showing students the overall goal of the mechanism?

As a recent PhD organic chemistry graduate and adjunct professor, I thought “Why not use the reaction scheme as the task card?” Students should know where they are going when they try to reason their way to the product.  Interestingly, many other instructors have shared similar thoughts during demos of Mechanisms. Now, however, I see the how this task card can help students by withholding information.

To develop mechanistic reasoning, the journey through the process is more important than the product itself. That’s why this post begins with the Arthur Ashe quote. It’s a lesson for more than just tennis or organic chemistry!

A recent study from Bhattacharyya group (see reference below) at Missouri State University makes a convincing argument regarding how mechanistic reasoning tasks are assessed. The group investigated if students used different strategies to solve electron-pushing tasks depending on whether the product was given or not. To conduct the study, they held think-aloud interviews with twenty-four students who were in an Organic Chemistry Semester II course. During the interview the participants were given the reactants for one step of a mechanism and were not shown the products of the transformation. They were asked to give the product of that step and show the mechanism for that transformation (Figure A). Later in the interview they were asked the same question, but this time they were also given the overall reaction scheme, that is, showing reactants going to products (Figure B).

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The researchers found that, in general, when the students were not given the product, they at least attempted to use their organic chemistry knowledge to reason their way to an answer. Conversely, as best stated by the authors, “When provided with the overall transformation, however, the students changed their focus to getting to the product. Consequently, they replaced correct answers with incorrect ones when given the reaction products.”

Our goal with the Mechanisms app is to help students build their mechanistic reasoning skills. By not showing the reaction scheme and the product on the task card, we remove the ability for students to use an “ends-means analysis”. Instead, students are encouraged to use their knowledge of organic chemistry to find the reaction pathway. They also do not need to worry about being penalized for a wrong move. They can make a hypothesis at each step, test it, and if it is a common error even get feedback about why that move is wrong and how to fix it.

With Mechanisms there is no pressure to get to the “right” product. Success is achieved in the doing, not the outcome.  Thanks, Arthur!

Reference: TMI (Too much information)! Effects of given information on organic chemistry students’ approaches to solving mechanism tasks. Bhattacharyya, G. and DeCocq, Chemistry Education Research and Practice (RSC Publishing), October 2018. https://pubs.rsc.org/en/Content/ArticleLanding/2018/RP/C8RP00214B#!divAbstract.

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