Many professors agree that a strong foundation of acid-base chemistry is vital for students to understand the great majority of organic reactions they will face, and I firmly agree. Certainly, the importance of acid-base chemistry is reflected by the fact that organic textbooks typically discuss acids, bases, and proton transfer reactions early. Despite these early discussions, I have heard from numerous professors over the years about their frustrations with students not making the connections between acid-base chemistry and learning organic reactions. Why the continued frustrations, and what is the fix?
Two reasons come to mind as to why students can have trouble making these important connections. First, some books have excessively high expectations on a student’s ability to carry forward content from general chemistry. These books have one or two chapters that quickly review a multitude of general chemistry topics, including a relatively short presentation of acid-base chemistry. This is quite destructive for students because it does not provide a strong-enough foundation (read more here).
A number of textbooks, on the other hand, do have a robust treatment of acid-base chemistry in a dedicated chapter. But these books generally don’t show the explicit applications to new organic reactions and mechanisms until several chapters later, and students have difficulty making these connections on their own. I witnessed this first hand, unfortunately, in my first few years of teaching, when I was using a traditional, functional-group-organized book that had a dedicated acid-base chapter. My students seemed to come away from that chapter feeling that acid-base chemistry had no bearing on material that was to come.
My students today don’t have this problem. When they begin learning new elementary steps in Chapter 7, which falls on the heels of the acid-base chapter (Chapter 6), they immediately see the connections to the concepts from acid-base chemistry. This is facilitated primarily by two sections in Chapter 7: Section 7.1, “Mechanisms as Predictive Tools: The Proton Transfer Step Revisited,” and Section 7.8, “The Driving Force for Chemical Reactions.”
Early in Chapter 6, students learn how to use curved arrow notation as a descriptive tool to account for the formation and breaking of bonds. In Section 7.1, students revisit the curved arrow notation for a proton transfer reaction, this time focusing on why curved arrows are drawn with a particular directionality (i.e., from an electron-rich site to an electron-poor site). Students then apply that idea toward nine new elementary steps introduced in the next several sections of the chapter, so that this important idea is heavily reinforced and helpful connections are made right away.
Section 7.8 uses acid-base chemistry to emphasize and reinforce another crucial concept: charge stability. Charge stability is covered in-depth toward the end of Chapter 6 to explain relative acid and base strengths. A short while later in Section 7.8, students learn how charge stability is used to understand and make predictions about which side of a reaction is favored. Again, students see the applications to new organic reactions soon after first learning the concept in the context of acid-base chemistry.
This strategy has worked very well for me and my students over the years, establishing a seamless transition from acid-base chemistry to new organic elementary steps to more complex mechanisms. It gives students much-needed momentum as they delve into some of the more challenging aspects of the course. And it is, I’m convinced, one of the major reasons why my students have shown such tremendous improvement since I made the switch from a functional group organization to a mechanistic organization almost a decade ago.
-Joel Karty
