In organic chemistry, I find that arrows are critical to teach organic content in a mechanistic perspective because they tell the story of all organic transformations. I try to impress upon my students that the arrows in mechanisms can provide a clear indication of how to move electrons.

Mechanistically, students struggle with knowing the difference between moving electrons in the pi framework and the sigma framework. To combat the struggle, I teach resonance in the early part of fall semester. Our class is in a “flipped setting” comprised of clicker questions, problem-solving activities, and assigned worksheets. Through this constant practice, students gain clarity by looking at the bonds that are being broken and formed. Especially when a charge is present, the use of curved arrows helps students look at where the charge is moved within the reaction.

In Karty’s mechanistically organized text, students are exposed to resonance hybrids and resonance contributors in a methodic route, which I haven’t seen fully done in other textbooks. As a teacher, I feel that there is no value gained when a student plainly provides the answer. After teaching this course for four years, I see the necessity of students’ awareness of how to create the resonance hybrids and resonance contributors. In assigned worksheets, students are asked to complete and answer several questions, ranging from moderate to high levels of difficulty. For example, in the sequential question below, I ask students to do the following:

  • Draw all reasonable resonance structures of the following molecule. Please remember to add in all electron pairs, when needed.pic 1
  • Based on the reasonable resonance structures from the previous question, circle the structures that are the most significant resonance contributors to the resonance hybrid. What features make these circled structures the most significant resonance contributors?
  • Draw the resonance hybrid of the molecule that is discussed/shown.

The intention is for my students to see the full picture of resonance…both the electron movement and the resonance contribution. Along the same lines, students have a tough time comprehending tautomerization (Figure 1). Students understand how to identify the keto and the enol. However, they are confused about how the two are related. Further, they get blown away when the resonance is combined.

pic 2

Figure 1. Tautomerization

I try to use examples, such as Reactions 1 and 2, to help students see the entire picture about how resonance and tautomerization are not two different subtopics, but rather, are two intertwined concepts.

pic 3

Reaction 1. Resonance of Positive Charge – Electron Movement in Pi Framework

In Reaction 1, I spotlight the strongest contributor and the subsequently lesser contributors. Curved arrows are used to show electron movement, along with bond stability, as the reasoning behind the strongest resonance contributor. However, I try to challenge my students by not teaching them surface-level content. I try to combine basic mechanistic movements to help solidify the content.

Kerri_Post2_Proton movement_NEW


Reaction 2. Proton Transfer – Electron Movement in Sigma Framework

In Reaction 2, I spotlight how resonance is related to tautomerization. Because of resonance, the charge can be better stabilized when it moves from the carbon atom to the oxygen atom, thereby showing the importance of proton transfer and the restoration of stability in the structure.

Overall, Karty’s textbook, through its mechanistic organization, does a great job of reinforcing this material for my students. Karty uses the fluidity of his writing to tell stories about organic chemistry topics that highlight the important links between each of them. Not only does this method help my students understand the true significance of certain topics, such as tautomerization, which can be glossed over in other textbooks, but it also helps my students view the various concepts in our classroom as having concrete connections to one another, which is essential for them to fully learn and understand all this exciting material!

-Kerri Taylor, Columbus State University

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