Mechanisms Make Everything Easier

My first teaching responsibility upon coming to Northern Arizona University was our ten-week Organic Chemistry II summer course. Besides never having taught a summer ten-week session, I had never taught organic chemistry from Karty’s text. I was pleasantly surprised to find that Karty’s text was organized by mechanisms, making lecture preparation, and overall flow of the class, much easier. From an instructor’s standpoint, the organization of the second-half of the textbook conveyed a story that both assisted me in teaching the material thoroughly and provided a structure that forced student’s to understand mechanisms rather than memorize them.

Beginning the course with Chapter 17, I slowly unraveled the mechanistic similarities between different strong nucleophiles and polar π-systems, like aldehydes, ketones, imines, and nitriles. Chapter 18 keeps the electrophilic species constant while evaluating reactions with varying weak nucleophiles. Chapters 20 and 21 keep this trend going by alternating between the same strong and weak nucleophiles, but changing the electrophiles to include acid chlorides, anhydrides, esters, carboxylic acids, and amides. As we progressed from one chapter to the next, I constantly reminded the students of the similarities to the mechanisms and product outcomes. This simple staircase approach to introducing reactions in a mechanistic way simplified the organization of the course and lessened student confusion—compared to my experiences with previous texts. It also benefited the students in two ways: the daunting amount of reactions and mechanisms was, in fact, not daunting at all, and we had just covered four chapters of similar material. The latter was a huge morale boost for the students.

I am teaching this course once again, this time a section of nearly 220 students. I am following the same approach I had with the summer course and introducing the information as organized by Karty’s text. Though the class size has grown, Karty’s approach continues to work with these larger sections and the typical semester length allows for a slower pace and further elaboration on the mechanisms. As with the flow of aforementioned chapters, the story conveyed in Karty’s text continues to unfold in further chapters.

Chapter 22 introduces electrophilic aromatic substitution reactions and progresses through Chapter 23, allowing the students to build off the core concepts of aromatic substitution reactions. The only change I make to the texts’s layout is using Chapter 14 (Orbital Interactions 2) to introduce aromaticity and benzene basics before continuing onto simple mono-substituted Friedel-Crafts reactions and di-substituted reactions of nitrations, sulfonations, etc. From here, the transition into Diels-Alder reactions is a logical one, as we describe the reaction, mechanism, and the molecular-orbital theory behind this classic reaction.

While I change some of the chapters around to fit the way I present the tale, Karty includes all the pieces necessary to fill that story with the appropriate details. In second-semester organic chemistry, Chapters 13 and 14 are the only ones that I rearrange to suit the way I teach the course. Having covered Chapter 13 briefly in Organic Chemistry I, it works well dissected and used for a review/introduction to Chapters 17 and 19, while using Chapter 14 works as an introduction to Chapters 22 and 23.

Teaching second-semester organic chemistry should be taught mechanistically and Karty’s text does a fine job of organizing the material to do so. Karty lays out a story that flows well and links the large amount of reactions and concepts by their common mechanisms; making it easier to both teach and learn.

-Cliff Coss, Northern Arizona University

Click here to learn more about Prof. Coss

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