In my experience, when students are writing a reaction mechanism, the most common error is to form a strong base under acidic conditions or vice versa. I stress the importance of paying attention to reaction conditions in lecture, but the “function group” based textbook previously used at Western Washington University did not contain a section dedicated to explaining this concept. Looking back, the old text did not even include a section about how to write a mechanism or correctly use “curved arrow” notation. This is my first quarter teaching from Karty’s organic chemistry text, and I was pleased to find that there is a section dedicated to writing a reasonable reaction mechanism that addresses this common student error.
Chapter 8.6a explains the importance of taking reaction conditions into consideration when writing a mechanism. It gives examples of incorrect mechanisms and then shows the student how to fix the mechanism to match the conditions given. It then includes multiple in-text problems for the students to practice writing a mechanism under either acidic or basic conditions. I knew this section of the text would be instrumental in reducing errors on exam questions about familiar reaction mechanism, but I wasn’t expecting how helpful it would be for students working through unfamiliar reactions.
Recently, I had a student who was a biological anthropology major come to office hours and she wanted to work through problems 8.37 and 8.38 with me. These problems asked the student to draw a mechanism for the racemization of the alpha carbon under acidic and basic conditions.
At this point in the quarter, my students had worked though many proton transfer reactions, but I had not specifically covered this reaction. Previously, with the book organized by functional group, alpha carbon substitutions are not taught until the end of the third quarter. So, I was expecting the student to struggle through this problem. She started working though the base-catalyzed racemization. At one point she wanted to introduce a hydronium ion to protonate the enolate. She stopped herself and said, “Wait, that doesn’t make any sense, I’m using base.” She correctly finished the mechanism and then looked at me for confirmation. I was blown away! Not only had she correctly transferred protons but she had stopped herself from committing the most common student error. I told her that I was impressed, and that previous first quarter organic chemistry students would typically struggle with completing that problem. It became clear to me then that including this concept in the textbook had led me students to a better understanding of reaction mechanisms and predicting the mechanism of unknown reactions.
I am more convinced than ever that by switching to Karty’s Organic Chemistry: Principles and Mechanisms, our students are actually learning organic chemistry and not just memorizing it.
-Written by Jennifer Griffith, Western Washington University