In today’s class, I spoke about the value of retrosynthesis, which allows chemists to view mechanisms and organic reactions from their products to their starting material. Typically, students are not keen on retrosynthesis because: 1). the word is scary, and students are introduced to many other difficult-sounding concepts while learning it, and 2). the process is complex and can overwhelm beginners. These are a few of the main reasons why I have to remind myself, particularly when teaching retrosynthesis, that even though I have had years of practice with this material, my students are just getting their feet wet, so it’s important that I match their pace and meet them where they are.
One of the joys of retrosynthesis is that there is immense value in seeing a reaction from the point of view of the products. As an organic chemist, I often prefer working backward because I can design the synthesis with the goal of making the desired product in as high yield and purity as possible. To help convey this idea to my students, I suggest that they look at retrosynthesis like a story.
My young daughters are currently in love with “Goldilocks and the Three Bears,” so I decided to reference this tale in class. If we were to apply this children’s story to the concept of retrosynthesis, it would be like reading the story from the end to the beginning. In this case, we would see an embarrassed Goldilocks running away from the Bears’ home (the end), and then we would see the Bears getting ready to start their day (the beginning). This analogy fits in nicely with the idea of organic chemists using retrosynthesis to view mechanisms and reactions from the perspective of their end products to their starting material.
In addition, although I know that, traditionally, we can teach retrosynthesis as an isolated topic, I’ve found that there are certain limitations to doing so. This method requires that students know their reactions, conditions, and exceptions, but students don’t always know all of these different elements at once, because they’re constantly learning as they go. This is why I like to use Chapter 13 to review and reinforce topics from earlier chapters of the book, such as synthesis, and tie them back in with retrosynthesis, which is actually how I first learned retrosynthesis back when I was a student.
To help us do so, my students and I worked through a number of in-chapter problems from Chapter 13 together during lecture. For instance, I provided my students with a full rationale for the reactions in Problems 13.8 and 13.13. In the image of my heavily annotated notes below, I have both retrosynthetic and synthetic arrows drawn, which I then supplemented with a discussion of how both pathways can be used to complete the synthetic scheme (i.e. using both retrosynthesis and synthesis to “meet in the middle”), which will help students connect previously learned material with the new.
By helping my students practice the backward movement of retrosynthesis along with the forward movement of synthesis, I’m able to show them why retrosynthesis can be so powerful: it points to the bigger picture in organic chemistry, which is that each reagent has a working part and a key place in the reaction scheme. And the fact that I’m able to bolster my students’ understanding of these complex yet conquerable topics through real-world examples and analogies, as well as through lots of practice problems, demonstrates the power of metaphors for student learning and success, which is just another added plus.
-Kerri Taylor, Columbus State University
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