One thing I was really looking forward to when switching to Karty’s mechanistically organized text was how reactions involving alkenes would be addressed. I expected to see the reactions simply grouped by mechanism; for example, the electrophilic addition reaction mechanisms would be grouped together, as would the pericyclic reaction mechanisms and so on. Instead, I was thrilled to discover much greater nuance in the book’s organization and mechanistic approach. Not only are the chapters specific to certain mechanisms, but they also each focus on a particular intermediate step or product of that mechanism. I no longer have to sort out the mechanisms and intermediates for the sake of my students like I used to.
In all the functional group-based textbooks that I’ve dealt with in the past, there is always a chapter titled, “Reactions of Alkenes”. This chapter is a hodgepodge of every conceivable alkene addition reaction. Everything, and by that I mean, hydration (acid, mercury and boron catalyzed), halogenation, epoxidation, epoxide ring opening, hydrogenation, hydrohalogenation (acid and free radical), dihydroxylation and even oxidative cleavage, gets lumped into one way-too-dense chapter. The reactions are grouped according to functional group transformation, and while the mechanism is illustrated, the similarities between the different types of mechanisms are not addressed. This leads students to believe that each unique reaction has its own unique mechanism. To help the students find the similarities between the various reaction mechanisms, I would reorganize the chapter based on the mechanism involved or the intermediate formed. At first, this seemed to help a little bit. But from talking to my students and looking at their quiz scores, they were still very overwhelmed and discouraged.
Switching to Karty’s Organic Chemistry, I found that someone else had had the same idea and gone through the trouble of writing an entire textbook for me! Alkenes don’t need to be a barrage of seemingly unrelated, nonsensical mechanisms! Chapter 11 of the text deals exclusively with electrophilic addition reactions involving carbocation reaction intermediates while chapter 12 is solely devoted to electrophilic addition reactions with three-membered ring intermediates or products. This organization made it so much easier for students to find similarities between reagents and predict the reaction mechanism and product. Toward the end of each of the chapters, I stopped providing the mechanism on the PowerPoint slides during the lecture. Instead, I would put a reaction on the board and have the students predict the products and draw a reaction mechanism based on similarities to other reactions they had seen. What amazed me was that they were actually able to do it! They were able to predict the correct product and reaction mechanism even though they had never seen that specific reagent before. This never would have happened in previous quarters teaching from the functional group-based textbook.
Teaching from a textbook where the reactions of alkenes have been divided according to mechanism has been amazing. It has made my life as an instructor much easier. I no longer have to try to reorganize the chapter to get the concepts to flow and make sense. As a result, life has also been much easier for the students. They now approach the subject matter with confidence and exam averages are much higher than before. Overall, it’s been a huge improvement to the course!
-Jennifer Griffith, Western Washington University
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2 thoughts on “Life is Hard Enough. Why Teach Alkenes By Function?”
Just a pure curiosity, do you test your students on the mcpba epoxide mechanism? I teach a non-majors course and I tend to leave that one off tests since lining up all the arrows is a bit complicated. I love the mechanism though, I’m always tempted to stick it on there.
I briefly go over the mechanism in class, but I do not include it on exams. It is a bit tricky for them to keep all the arrows straight!