Teaching students how to think like a chemist is a challenging, but necessary feature of any organic chemistry course. A seemingly simple question such as, “How will these two compounds react when I mix them?” can stump even the best students. Since it is impossible to memorize every possible reaction combination, students must rely on and apply their knowledge of fundamental concepts. By organizing my course according to mechanism, the students develop a strong foundation of understanding that they can build upon, which makes learning to predict products a much more manageable task.
The first mechanism that students encounter in Karty’s Organic Chemistry: Principles and Mechanisms is the proton transfer reaction (Chapter 6). This ubiquitous reaction doesn’t normally get an entire chapter dedicated to it, but it’s the perfect springboard to get students into the chemist’s mindset. An in-depth treatment of this fundamental transformation provides a simple introduction to curved arrow notation which easily segues into the substitution reactions that follow in later chapters. Proton transfer reactions also clearly demonstrate the relationship between stability, chemical reactivity and free energy changes through a discussion of pKa values. First, students learn how to compare pKa values of different compounds by considering the stability of the conjugate base, applying their knowledge of resonance and inductive effects. Next, they use differences in pKas to estimate the position of equilibrium in proton-transfer reactions. As the course progresses to more complex, multi-step mechanisms, they can continue to use pKa values to make predictions. For example, determining the order of mechanistic steps in an acid-mediated acetal forming reaction can be greatly simplified by using pKa values as a guiding principle.
This is just one example of the benefits of teaching a mechanistically organized organic chemistry course. It allows students to more easily draw connections between the fundamental principles they learn early in the semester to the more complicated problems encountered later in their journey. This scaffold helps students to better understand the bigger picture in a chemical reaction and to think more like a chemist.
-Dr. Anne Szklarski, King’s College
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