Memorization Not a Choice: Mechanisms Matter

I have always approached my organic sequence as a mechanism-driven course. Every reaction that we discussed in class started with a mechanism to show how it wasn’t really anything new, but an extension of the types of behaviors we had learned to describe and anticipate. I avoided texts that listed reaction after reaction as completely new equations in huge lists, and tried to find texts with the best descriptions of mechanisms I could. Even so, I often felt that I was fighting the textbook, trying to impose my worldview onto a structure that didn’t really support it.

When I first read Joel Karty’s text, I knew it fit what I was trying to do. I loved how Chapter 6, proton transfer reactions, was organized and presented as not just the acid/base chapter but as the starting point for mechanisms. Chapter 7 introduced the other simple mechanistic steps in one amazing sequence. The first time I read Chapter 7 I was so excited—there it was, everything I’d been trying to do, put in clear prose. Here was a text that I wouldn’t have to fight, something that took what I was working towards and went further. Mechanisms are set up as the heart and soul of the course, with everything else flowing from these steps and chapters. That being said, I was terrified to actually put it into practice.

Chapter 7 covers all the simple mechanistic steps, including topics that I had never introduced in the first semester, like nucleophilic addition and nucleophilic elimination. It seemed like a lot of information to introduce all at once. But reorganizing one’s approach to organic chemistry doesn’t just mean changing how the topics are taught, it also means changing when the topics are taught. If mechanisms really mattered to me more than memorization of reactions, I needed to move past the organization by functional group. I had a hard time imagining how that would work in my classroom, since I had always followed the same progression of topics, building on molecular complexity from alkyl halides to alcohols to alkenes and so on. With Joel’s approach, all functional groups are used in mechanistic steps and problems right away. There are no artificial limits, where the problems include only alkyl halides or only alcohols. We dive into diverse systems right away, showing how they all follow the same predictable simple mechanistic steps. Would my students follow so early in the semester, or be overwhelmed?

It worked and better than I had imagined it could. The students didn’t realize they were learning topics ‘out of sequence,’ nor did they feel that they were being introduced to too much at once. I had always thought of carbonyl chemistry as an advanced topic because of when it would appear in my sequence with other texts (starting around February). February was typically when many of my students would start to struggle with remembering all the information, just as we approached the topic where all the ideas we’d studied started to come together. Despite my best efforts, there were always students who blindly memorized and here it would start to fall apart.

Using Joel’s text, my students were much less likely to try to memorize everything. They had no choice but to learn the mechanism. With that foundation, the reagents and functional group transformation was much easier for them. Not only did they do well with all the steps in Chapter 7, when carbonyl chemistry first appears along with every simple mechanistic step, they did much better throughout the spring when the number of reagents we’d learned became large and somewhat intimidating. This year, the class average on the ACS’s standardized final exam was five percentile points higher than my previous five-year average. With a foundation of mechanistic understanding, my students simply performed better.

This semester I have given more time to Chapters 6 and 7, treating them like the fundamental groundwork they are. I worried last year about how late I would be teaching SN1/SN2 and E1/E2 (Chapter 8), but it turns out that Chapter 8 is a breeze if they really understand Chapter 7. I know that every minute I spend with Chapter 7 is time well-spent and ultimately time saved for later in the semester and the spring. If they understand the mechanism everything else is just variations on those themes.

-Michelle Boucher, Utica College

Click here to learn more about Prof. Boucher

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