Predicting the Products of an SN1/SN2/E1/E2 Competition

When I teach nucleophilic substitution and elimination reactions, I find that students typically have very little trouble drawing each mechanism and predicting the products, so long as they are specifically told which reaction. But many students find one aspect very challenging: predicting the winner of an SN1/SN2/E1/E2 competition. In my first few years of teaching, I dreaded giving and grading my second exam, the exam that covered this reaction competition. Many good students would receive a very low grade, thus creating poor class morale for the rest of the semester. The SN1/SN2/E1/E2-competition exam was the exam where many pre-health students decided that their fate was sealed. In the years since then I have turned things around considerably. What did I learn? And what did I change?

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The Chapter Every Organic Textbook Should Have

This unique chapter is the game changer for how students perceive organic reactions. Whenever I discuss Joel’s textbook with colleagues, this chapter is the first aspect of the book that I mention.

Chapter 7, “An Overview of the Most Common Elementary Steps,” briefly surveys ten steps:

  • Proton transfer
  • SN2
  • Bond formation (coordination)
  • Bond breaking (heterolysis)
  • E2
  • Addition of a nucleophile to a polar pi bond
  • Elimination to form a polar pi bond
  • Addition of an electrophile to a nonpolar pi bond
  • Elimination of an electrophile to form a nonpolar pi bond
  • Carbocation rearrangements

This survey covers the elementary steps that students will see in a reaction mechanism until they study pericyclic reactions and reactions involving free radicals.

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Why Mechanisms? [Video]


Why did Elon professor Joel Karty decide to author a textbook organized by mechanisms? Prof. Karty talks about how his frustration with teaching from a traditional, functional-group organized textbook spurred him to reorganize his course and to write his book.

What does it mean to be mechanistically organized book? What advantages does a mechanistic organization offer? Watch Joel’s other videos to find out.

On Nomenclature

In my first few years as a professor, I taught nomenclature in the way it was organized in the textbook I was using at the time—i.e., according to functional group. Each time my class began a new functional group chapter, I would teach aspects of nomenclature associated with that functional group. Indeed, I found this to be a very tidy way of organizing nomenclature because the rules of nomenclature themselves are based on functional groups. But despite spending a substantial amount of time in class on the topic—about 2–3 lecture periods in total throughout the year—my students were underperforming on their exams. Today, teaching the entire course under a mechanistic organization, I deal with nomenclature very differently. In my textbook, nomenclature is fully separated from the main chapters that deal with actual chemistry (structure, stability, reactions, etc.) and is organized according to nomenclature rules, not functional groups. My students are assigned to learn most of that material on their own; I spend just a portion of one lecture period on it. As a result, I am finding that my students perform much better on nomenclature on their exams. The take-home lesson is that “tidy” does not always mean “best.”

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Nomenclature As An Independent Topic

When I first saw nomenclature presented as four independent chapters, instead of as small sections within functional group chapters, I reacted negatively. Who wants to teach multiple topics in nomenclature in one class period?  Shouldn’t students be exposed to the material over time, developing their skills incrementally, similar to what occurs in a language class?  And don’t students deserve those “easy” problems about nomenclature at the beginning of each exam?

However, when I taught the course using Joel’s early draft of the textbook, I found that knocking out nomenclature quickly and in large chunks works well for students.  Naming compounds is, after all, an algorithmic process that follows rules.  As you go from naming compounds with one functional group to those with a different functional group, the only significant changes in the name are the prefixes and suffixes.

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Molecular Modeling Kits

For many students, the three-dimensional nature of organic chemistry raises the difficulty of the course to a new level. This difficulty stems from the fact that the three dimensionality of a molecule is depicted on a two-dimensional surface using any of a variety of representations. Accepted representations include dash-wedge notation, sawhorse projections, Newman projections, Fischer projections, Haworth projections, and chair representations. Even some of the most basic problems in organic chemistry may require a student to convert a two-dimensional representation of a molecule into three dimensions, carry out a particular manipulation of the molecule, and then return the molecule back to a two-dimensional representation in order to provide an answer. Some students can carry out these tasks in their head with no trouble, but I have found over the years that the large majority of students cannot. So then, how do we help these students?

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