Playing Musical Chairs with Spectroscopy

As a Synthetic Organic Chemist by trade, I use NMR spectroscopy heavily for analysis and structure identification. When designing a course in organic chemistry, it comes as no surprise that I want my students to be comfortable mining information from an NMR spectrum and using it to solve problems. A mechanistically organized course lends itself well to teaching spectroscopy early, both for organizational and conceptual reasons.

Utilizing NMR analysis early and often in the laboratory serves as a valuable complement to coursework because it empowers students to evaluate some of the theories they are learning in a practical setting. Placing spectroscopy early in the course syllabus makes a lot of sense for the lecture as well. A discussion of the factors that affect the chemical shift of a proton is an excellent application to see the importance and influence of topics in structure and bonding (like electronegativity, hybridization, and functional groups). While the semester often begins with topics that review what students have learned in general chemistry, spectroscopy challenges them early in the course. It even stimulates conversations with advanced students who might otherwise be bored. Unknown identification through spectroscopy provides a puzzle that is unlike many of the problems students have been exposed to thus far, setting the tone for critical analysis of data throughout the semester.

Unfortunately, traditional textbooks hold off on spectroscopic analysis until midway through the book. When I have used texts that are organized by functional group, they often spread the topic out even further by incorporating spectroscopic information specific to a functional group in later chapters. If I wanted to teach NMR at the beginning of the course, I had to consolidate everything into supplemental handouts and warn students that they may not be able to do certain problems in the book that required knowledge of reagents. This led to frustration on the part of the students; they were hungry for more practice problems but were unable to sort through the book’s confusing arrangement.

The mechanistic approach employed in Joel’s book serves as a much more effective resource for my students and gives me the freedom to relocate the NMR and IR spectroscopy chapters to the first three weeks of the course.  Because the organization does not depend on functional groups, these topics are more self-contained and can stand alone at any point in the course. There are plenty of practice problems in the book that I feel comfortable assigning and students can use others as resources if desired.

Beyond simply an organizational advantage, I found several aspects of Joel’s discussion of NMR that were very helpful. The Study Guide and Solutions Manual is particularly useful for unknown identification because it not only contains the correct structure, but it also includes a step-by-step description of a good approach to solving these problems and the rationale for peak assignments. For a confused student, this is the next best thing to working through problems in my office.

Additionally, the chapter discusses both the fundamental process that produces an NMR spectrum and analysis of the data.  I find many textbooks lacking information about the former and students try to get by with memorizing patterns and chemical shifts without knowing what these peaks truly represent. In a sense, they treat the spectrum as somehow separate from the compound it represents and are overwhelmed with too many possible structural arrangements. The connections that form with an understanding of the underlying concepts of NMR allow students to more clearly recognize similarities between a structure and its spectrum rather than starting each problem with a blank slate.

In my experience, the earlier my students are exposed to NMR, the better. They do not need to have an understanding of mechanisms or reactions to approach NMR problems, but a solid grasp of spectroscopy helps inform some of the bigger concepts they learn throughout the year. I have found that the mechanistic approach to organic chemistry empowers students to look at spectroscopy problems in a holistic way, rather than artificially categorizing the topic into functional groups. As a result, students can utilize NMR data as evidence for success in the laboratory and as a tool to reason through synthetic problems throughout the course. This communicates the strong tie between the mechanistic predictions we discuss in class with the experimental results obtained in real-world situations.

-Laura Wysocki, Wabash College

Click here to learn more about Prof. Wysocki.

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