Organically Gaining Synthetic Expertise

I started teaching Karty’s textbook in my first full-time teaching position, and I am not looking back. At the end of each semester as I review my course plan and think about what worked that semester and what didn’t, I always notice new ways in which this textbook design is smart, student-centered, and ultimately makes my job easier. The way the textbook addresses synthesis problems is just the latest example. Karty devotes two chapters at strategic points in the book to teaching synthesis, but this is really just the start of how his design is perfect for this topic.

As an organic chemistry professor, one of the end goals that I set for my students is that they will be able to propose a multi-step total synthesis for a moderately complex molecule. This skill is one many organic professors strive for because it allows our students to showcase a broad understanding of a variety of reactions. To be proficient in this skill, students have to know a large number of organic transformations, and more importantly, they need to recognize the advantages and limitations for each. For example, if our goal is to synthesize a primary alcohol, we have to know that oxymercuration/reduction or acid catalyzed hydration are poor choices (these lead to secondary or tertiary alcohols), while hydroboration/ oxidation is a likely tool that will be used.

In my courses, I often reach Karty’s first organic synthesis chapter (Chapter 13) towards the start of the second semester (Organic II), so I largely ignore the concept of a multi-step synthesis until that point. For my students, this pace actually works out perfectly because when they return from winter break we get to take time reviewing their first semester reactions while putting them into the context of useful tools towards building molecules. This initial taste of synthesis also helps to reinforce the importance of the content the students are learning. They realize that the reactions they are seeing are not just there to fill pages of a textbook, but instead can be used in meaningful applications.

Teaching synthesis at the mid-point in organic chemistry can have some challenges. The biggest issue is that students have really only begun to learn the practical reactions that are useful in a multi-step synthesis. This limits the examples we can provide to reinforce the concept. However, with Karty’s text, students do get exposed to some of the more “interesting” transformations earlier. For example, in chapter 10 students see alpha alkylations and halogenations, practical applications of an SN2 reaction. This topic often shows up in the middle of Organic II if you follow a functional group approach. I find that by that first synthesis chapter there is actually a breadth of material to work with to begin building an understanding of complex syntheses. Rather than an introduction in functional groups one at a time, typically confined to one or two chapters, students see these functional groups in different settings at various points of the semesters. This helps to bridge the relationships between functional groups and students start to think of groups not just as a starting material or a product, but also as a useful intermediate.

Later in the semester, once the students have really built up their “organic toolbox,” we get to revisit the concept of synthesis again as a separate chapter and learn additional strategies to apply synthesis in practice. Karty’s approach to introducing synthesis through these two chapters is unique and I have found that this is an excellent approach to ease my students into the topic. I see a growing appreciation for the reactions the students are learning as we move through the semester. They enjoy the “break” of the synthesis chapters where the amount of “new” content is low. Instead of absorbing new reactions, they get to practice what they’ve learned already.

I think for most students, developing a multi-step synthesis will always be one of the toughest parts of an organic class. However, with cleverly timed introductions to this skill and reinforcement throughout multiple chapters as in Joel’s book, our students often surprise themselves with their synthetic expertise.

-Jamie Ludwig, Rider University

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The Mechanism Did It!

I finally finished the book last night. In the two years since we adopted Karty, I have taught the first-semester course three times. However, due to the oddities of academic scheduling, this spring was my first time teaching our second-semester course with the text. So, metaphorically speaking, I finally got my chance to find out how the book ends; I got to see how the text works for second-semester curriculum.

Unlike an Agatha Christie mystery novel, the ending—though enjoyable—was not filled with intrigue and suspense. Of course, any instructor who comes within twenty meters of Karty’s text knows immediately that the reaction mechanism is the central, and perhaps only, protagonist. I recently had a very illuminating conversation with a small group of students who described their own discovery of this literary analogy.

These students had taken the first-semester course with me a year ago, but elected to take biochemistry before returning to organic. This trajectory is, in fact, not at all discouraged by our new curriculum. I was eager to hear their views about getting back into the organic chemistry mindset after an eight-month break. I got comments like:  “It came back pretty quickly” and “Going over the new mechanisms helped you to remember everything you learned before” and “Everything still made sense with how reactions worked…I didn’t have to review really.” These comments would have been nice to hear from any students, but were even better from students who had taken such a long break from organic. I was pleased but not surprised. With less to memorize, there is less to forget.

For our last class today, we went through E. J. Corey’s 1969 total synthesis of Prostaglandin F2a. It was like a Greatest Hits compilation for organic synthesis. Substitution, oxidation, reduction, Diels-Alder, Wittig, carbonyl addition, hydrolysis, protecting groups, and more. Students smiled as they met familiar old friends and more recent ones. A few even cheered for the Wittig—a class favorite. It all made sense to them because they had carefully followed Karty’s main character though each chapter.

Yes, the mechanism did it alright. A great ending to the story. Sure, there is more than one mechanism in organic chemistry. Many in fact. From the student’s point of view though, once you know mechanisms, you know organic chemistry. The rest just seems natural.

-Rick Bunt, Middlebury College

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My Surprising Favorite Second-Semester Chapter

My favorite chapter of second-semester organic chemistry is perhaps more surprising to me than anyone else, considering all the great mechanisms and reactions that fill the second-half of Karty’s textbook. My enjoyment of Chapter 16 (“Structure Determination 2: Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry”) is most likely due to my own experiences analyzing complex NMR data of carbohydrates, lipids, and peptides. Affectionately known as the “NMR Chapter,” Chapter 16 is briefly covered in the final week of our first-semester organic chemistry course, but is further expanded on and put to use in the first week of the second-semester.

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All Downhill After the Aldol

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.

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Favorite First-Semester Chapter: Chapter 9

My favorite chapter to teach in first-semester organic chemistry has to be Chapter 9 (“Nucleophilic Substitution and Elimination Reactions 1”) from Karty’s text. The introductions of S­N2/E2 and SN1/E1 reactions begin in Chapters 7 and 8, respectively, but Chapter 9 puts these reactions to the test and suggests to the students that reactions do not always work as planned. Competition reactions occur in nearly every real-world synthesis and the competitions between simple substitutions and eliminations are the students’ first exposure to the challenges of being a synthetic chemist.

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Building on their Knowledge: From Atoms to Multi-Step Synthesis to Curing Sick Puppies

Karty’s mechanistic approach to organic chemistry provides the content organization to facilitate student success. In a functional group approach students are more likely to apply an incorrect mechanism to solve a synthetic problem. This is because classification by functional group does not provide an organizational level that allows students to classify reactivity. Organization by functional group relies more on remembering molecular structure than on analyzing the structure for key reactive areas. Thus, a mechanistic organization is given a higher mark on Bloom’s taxonomy of learning and leads to a deeper level of student understanding. A mechanistic organization also conditions students to immediately apply previously mastered concepts in order to solve more complex problems. Homing in on functional group rather than rationalizing reactivity greatly diminishes the variety of problems a student can solve.

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My Most Productive Start of the Semester Ever

The first time I taught out of Joel’s text, I had no idea where I was going to put the semester break. I enjoyed how well each chapter flowed into the next, but that left me wondering where to put a five-week break. I was used to a traditional ordering of subject which resulted in the first semester ending with alkynes, and the second semester starting with oxidation and reduction reagents. With Karty, I planned to start my second semester with a review of Chapter 7, “An Overview of the Most Common Elementary Steps.” As Nathan Duncan wrote about in his post “An Easy Transition into the Second Semester,” Chapter 7 is a great way to refresh students’ memories and set the stage for the new material, since it allows us to revisit the heart of the text and the course. But refresh student’s memories from where into what?

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