Surprises from Chapter 10

Organizing a course like organic chemistry with dense material and volumes of content to cover can be incredibly daunting. At times, it seems impossible to find a balance between giving fundamental concepts the attention they require and building up the toolbox of reactions for students to use at a reasonable pace. Like many professors, I have always maintained that learning organic chemistry must be based in the connections drawn among reactions to create a larger roadmap rather than in sheer memorization. For me, those connections have a strong basis in mechanisms, which means spending a significant amount of time learning the timeless questions of organic chemistry, like what is a strong base, where do you draw the line for a good vs. a poor nucleophile, how do you know if something is “stable,” and how can you recognize an electrophilic site?

With Joel Karty’s mechanistically-organized book, I have found the opportunity to explore these questions thoroughly. Memorization of reagents wasn’t even possible until the tenth week of the semester in the context of applied SN2/SN1/E2/E1 reactions. When we reached this point, I realized a few surprising things. I had budgeted four class periods to cover all those reactions, but when it came to preparing materials, I found that I didn’t have many new things to say. The reactions that students traditionally struggle with, and eventually methodically memorize, were simply the same mechanism we had been talking about for a week and a half, but under specific conditions. At times, I was even worried students would get bored with yet another example of this obviously useful SN2 mechanism. However, with a strong mechanistic foundation, group work became more productive, parallels with other reactions could be quickly identified, and students worked through new applications more independently. In my experience using a textbook organized by functional group, the number of reactions introduced in Chapter 10 would have been overwhelming. With the mechanistic organization, students were able to incorporate “new” reactions in stride because there wasn’t much new about them—they were already familiar with the mechanism.

Another surprise came when I was grading quizzes and exams for the SN1/SN2/E1/E2 chapters. Usually, when students don’t know the answer to a question, I see the chemistry equivalent of gibberish. Arrows that don’t make sense, carbons with five bonds, made-up reagents (sometimes including “magic”), and bonds spontaneously cleaving. This year, when students got questions incorrect, most of the time their answers could be explained: they misidentified the electrophilic site, forgot to consider acid-base reactions, invoked an unstable intermediate, or drew a minor product instead of the major product. These are welcome mistakes because they lead to critical learning opportunities and conversations about how reactions progress and why certain reagents are required in a situation. This is in stark contrast to previous years, when I frequently encountered the dead-end response that the student just didn’t remember the answer.

In fact, my biggest unexpected frustration using a mechanistic approach is that students want to draw the arrows for almost EVERYTHING. In the interest of time management on exams, I have had to encourage several students to practice writing just the reagents and products in a synthesis sequence. This has met with some resistance because, after all, they depend on the arrows to remind them what the product should be. I never thought I would be in a position to encourage a little bit of memorization, but I am thrilled that my students are approaching problem-solving in organic chemistry with an eye for the fundamentals.

As we move forward through Chapters 11 and 12 in the course, I still have the feeling that we’re not introducing many earth-shattering new concepts. Now when we have a new reaction to consider, we take the time to think about stereospecificity, regioselectivity, and its relationship to previous topics. With a firm base in mechanisms, we are able to ask interesting questions about new situations instead of having the breathless feeling of racing through new material to reach a certain point at the end of the semester. And the results of the dreaded Exam 3, which deals with with SN1/SN2/E1/E2 reactions? The class average was the highest I have seen in my four years of teaching Organic Chemistry I.

-Laura Wysocki, Wabash College

Click here to learn more about Prof. Wysocki.

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