A Mechanistic Organization and Learning Synthesis: Having Cake and Eating It, Too

When I began teaching organic chemistry over twelve years ago, I adopted a traditional textbook organized according to functional group. The concept of organic synthesis was introduced in a short section in Chapter 4, as was retrosynthetic analysis. The intention, I think, was good: with these aspects of synthesis introduced early, students would incorporate new reactions in synthesis as the reactions were encountered in subsequent chapters. The idea was to revisit synthesis repeatedly, which would presumably hone students’ skills in synthesis design. But that’s not what I was witnessing in my own classroom. To the contrary, my students were struggling with synthesis, and it’s no surprise why.

To my students, mechanisms were nowhere to be found in a synthesis, so why should mechanisms matter? As I outlined in a previous blog post (Functional Groups, Mechanisms, and Memorization), this circumventing of reaction mechanisms lead to difficulty mastering reactions in general and left them with no choice but to memorize. And if they were having trouble with reactions in the forward direction, why should they excel in synthesis, which requires students to work with reactions in the reverse direction? The heavy emphasis on synthesis was, ironically, proving to be counterproductive to my students’ mastery of the topic.

The measures I take in my book are designed to help students excel in synthesis in addition to mastering mechanisms. First, the introduction of synthesis is delayed until after students have a solid foundation of reaction mechanisms. Second, the mechanistic organization of my book naturally focuses students on mechanisms, so students are more competent with reactions in the forward direction, including regiochemistry and stereochemistry of reactions. Thus, students are better equipped to work with reactions in the reverse direction. Third, there are two chapters devoted to synthesis, giving students ample time to learn and digest the material.

In the devoted synthesis chapters, moreover, vital topics are covered, including ones that are often taken for granted. For example, students work through the differences between writing a synthesis and drawing a mechanism. In addition, students are taught explicitly about the importance of including the counterion when supplying a reagent. Students also learn to categorize reactions according to whether or not the reaction changes the structure of the carbon backbone. These fundamentals of synthesis design help set students up for success with more intermediate topics covered later, including using protecting groups and identifying the relative positioning of functional groups in a target to determine which carbon-carbon bond formation reactions could be used.

Teaching synthesis under a mechanistic organization, I have seen my students perform better at synthesis design than they did under a functional-group organization. As it pertains to their success, therefore, this is a case of my students “having their cake and eating it, too.”

-Joel Karty

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