The other day, while working through Chapter 21, I left class with a great feeling as a result of having given the following clicker question:
My students were able to rule out choice (a) on their own, given that there’s no reasonable mechanism to arrive at that product with the methyl groups located there. However, they had trouble choosing between (b) and (c). I wasn’t surprised at their struggle because those compounds are the products of two similar mechanisms: (b) is the product of an intramolecular Claisen-type reaction and (c) is the product of an intramolecular aldol addition. Furthermore, each reaction has produced a relatively stable six-membered ring. So if my students had difficulty with this question, why did I leave class with a great feeling? It was because of what happened next.
Ah yes, it is that time of year again; a seven week coast to the Organic Chemistry II finish line. All the elementary steps have been introduced and discussed multiple times and it feels like review from here. Most texts seem to end with reactions like Aldol condensation and Robinson Annulation. A functional group approach to organic chemistry forces these key carbon-carbon bond forming reactions to be at the end of the second semester because they do not create a simple functional group like an alkene, aldehyde, or an amine. This leaves little time for them to be reviewed via retrosynthetic analysis problems in future chapters. How are chemists going to be appropriately trained when all C-C bond forming reactions are forced to be covered last? How are we to make anything interesting without access to them? Joel’s text doesn’t create this problem.
There were two places in Joel’s text that surprised me: where 1,2 versus 1,4 addition to a conjugated diene appeared—Chapter 11—and where direct versus conjugate nucleophilic addition to polar pi bonds appeared—Chapter 17. Both of these chapters introduce basic concepts and then expand all the way to complex applications, much further than a functional-group organized text would go right away. I was worried that this seemingly vast amount of material would be too much for students to handle, but I was wrong.
I’ve noticed over the years that when I put a “name” on something, students tend to panic. We will be doing just fine with SN2 reactions, but when I suddenly name it the Williamson Ether Synthesis, my students become very concerned, as if it’s some completely different concept. Whenever I bring up the Williamson Ether Synthesis later in the course, they don’t know what I’m talking about and suddenly can’t do a straightforward SN2 reaction anymore. Perhaps you have noticed this with other named reactions, too.
A similar thing would happen about midway through second semester when we would start dealing with the reactions of enolates, which was usually given its own chapter in the text. Even though it’s just another nucleophile, students became very concerned with this “new” entity. Students compartmentalized it into its own arena where it looked and acted differently from every other reaction they’d seen before. They thought they had a completely different set of confusing reactions. We had put the enolate on a pedestal. Yet when my department switched to Karty’s text, I suddenly noticed my students no longer really had a problem with enolates. Karty has taken the enolate off of the pedestal.
As a new professor, I had mixed feelings about spring break. On the one hand, I was so ready for a vacation, but on the other, I remembered what it was like as a student that time of year. Your mind is on anything but classes. Not only are you looking forward to a week at the beach (or at least anywhere but campus), but you’re also starting to see summer on the horizon. For organic students who have made it through a semester and a half of a tough subject, it’s easy to understand why many of them “check out.” That’s why I felt a bit apprehensive about scheduling exam two the Friday after my students returned from break. Not only was I asking them to jump right back into organic full swing, but the material we had covered for this second exam was definitely not trivial (not that there is really a “trivial” chapter in organic!).
Exam two covered chapters 17-20 of Principles and Mechanisms, and if you’re familiar with the textbook, you know this is quite a bit of material. However, we got through the exam with few complaints. A few days later, I entered the grades into the grade book and started to suspect that I’d done something wrong. The average for this test was about 5% higher than any of my previous exams throughout the year. While there could be multiple contributing factors for this jump in scores, I can’t help but attribute most of it to the hard work of my students and the success we’ve seen with a mechanistically organized course.
Elon University is located in central North Carolina and we don’t often have severe winter storms. In fact, in my previous 12 years at Elon, not once did we have a cancelled day of classes during our fall or spring semesters. This spring semester, however, four days of classes were lost to winter storms, three of which were on days I teach my Organic 2 class. Based on how I designed my syllabus, I figured I could sacrifice one or two days of class, but certainly not three. I found myself in a position in which I had to make up at least one entire class period worth of material. I decided to accelerate the class somewhat for the next few meetings. To accomplish this, I gave students, ahead of time, several clicker questions that I would normally present for the first time during class. I asked students to solve the problems on their own, after having read assigned sections from the textbook. During class, I didn’t need to use the time they otherwise would use to solve the problem and submit their answers. Furthermore, I cut down on the time spent in class we would typically devote to discussing each of the clicker questions.
In my mind, enolate chemistry is one of the highlights of the second-semester organic chemistry course. Granted, the list of named enolate-based reactions (Aldol, Claisen, Michael, Robinson, etc.) can be daunting to students. Nevertheless, the importance of enolate chemistry in biochemical processes (glycolysis, gluconeogenesis, fatty acid biosynthesis), as well as in the synthesis of compounds of interest to both the pharmaceutical (Tamoxifen, progesterone) and personal-care (jasmone, b-vetivone) industries, has in my experience been manifold in convincing students of the relevance of organic chemistry to their curricular and career plans.
Unfortunately, most texts (and by extension most courses) place enolate chemistry into a one- or two-chapter unit near the end—it’s often one of the last things that students see in the year-long organic chemistry sequence. I have two concerns with this long-standing organization. First, students often see these important reactions at a time of year when both their energy and motivation are low. Second (and worse in my opinion), students see enolate chemistry separated from other mechanistically-related reactions. Year after year, I have seen this combination work against students. Encountering disconnected enolate chemistry when they are fatigued, they rely on memorization rather than mechanism to move through the unit. The net result? Increased anxiety and lower exam scores.