The new year traditionally brings a time for both reflection and looking forward. For teachers of organic chemistry everywhere, this past year stands out more than most. After years of planning, MCAT-2015 is finally upon us. I previously wrote about the challenges and opportunities this change holds for us and how we, at Middlebury College, were planning to adapt. So as we greet 2015, it seems appropriate to reflect on how the first semester teaching our new organic chemistry curriculum with Joel’s textbook went and to see what lies ahead.
In my previous post, I described how happy I’ve been with my students’ ability to process the relatively complex interplay between kinetics and thermodynamics to understand the outcome of a competing set of chemical reactions. The specific example I gave involved the competition between transesterification and the Claisen condensation reaction, and that got me thinking about how far my students have come since they first started learning organic reactions last semester. In Chapter 7 of my book, students are given an overview of the ten most common elementary steps in organic reaction mechanisms—the same elementary steps that make up transesterification and the Claisen condensation reaction. Nevertheless, I don’t think students should be expected to deal with these kinds of complexities immediately after learning the elementary steps—they are simply not ready. Instead, students need time to digest what they learned in Chapter 7, and they also need significant scaffolding of additional material before being held accountable for these higher level decision making processes—material such as: how to incorporate proton transfer steps reasonably in a mechanism, relative nucleophile strengths, reversibility, and the ideas surrounding kinetic versus thermodynamic control.
What, then, should students be expected to do upon completing Chapter 7? I think it boils down to the following:
A week ago, one of my students sent me this in an email:
“I have a question for you: when an ester and an alkoxide anion are together in a problem, how do we know if a transesterification or a Claisen condensation will take place? Is it just that if the alkoxide anion is the same as the ether group (so a transesterification would reproduce the base)?”
Here is what I wrote back to him:
“Both will occur…they will compete. Transesterification might be faster, but it is reversible. Claisen condensation might be slower, but it is irreversible. So what will happen is the OR groups from the initial ester and from the added base will scramble, and eventually all of the product will be from Claisen condensation.”
In his next email to me, he wrote my three favorite words to hear from a student: “That makes sense!”