Why a Mechanistic Organization Improves Understanding in Large Lectures

One of my favorite TV commercials is the AT&T, “Bigger is Better, It’s Not that Complicated” ad that features unscripted responses of elementary school children about why faster, bigger, larger, etc. is better.  Unlike cell coverage, bigger lecture size is not necessarily better. Over the years, I have done a number of things to make a large lecture more manageable, but my switch from a functional group organization to a mechanistic organization made the most noticeable difference.

At Old Dominion University, I teach sections of organic chemistry that average 300 students. There are many challenges to teaching such a large lecture. It is more difficult to communicate with each student, students are less likely to ask questions during lecture, and they often leave lecture without a full understanding of the day’s objectives. Students in a large lecture class are often forced to do more learning on their own because of the limitation of my time. Concerned, I started to use clickers (an interactive response system) in my lecture to monitor student understanding. I discovered students struggled to understand any mechanism longer than 1-2 steps, were not equipped with the skills to approach a new problem, and often “forgot” about topics in previous chapters.

With the functional group approach, I felt as if I was dumping a lot of information on them at once. For example, the alkyl halide chapter includes nomenclature, physical properties, synthesis, and S_N1, S_N2, E1 and E2 mechanisms. No connections are made between each mechanism and the students approached the mechanism as if each one is something new to memorize. Students frantically wrote everything down (without much comprehension), and figured they would memorize the material later. Participation was low and it felt as if everyone was just trying to get through the lecture. When I switched from the functional group organization to a course organized by mechanism, I noticed that more of my students were engaged, understood the reading material, and approached multistep mechanisms with more confidence. Mechanistic organization helps students build critical thinking skills and teaches them how to problem solve. More students are more confident which results in a higher level of student engagement.

The ease at which students can determine the reasonableness of a mechanism is noticeably improved with mechanistic organization. For example, if a reaction is conducted in acidic media, strong bases are not permitted in a mechanism and vice versa. In the S_N1 reaction, (CH₃)₃COH + HBr à (CH₃)₃Br + H₂O, the reaction medium is acidic and the mechanism involves three steps—proton transfer, heterolysis, and coordination.  I found that most students can memorize that HO⁻ is a bad leaving group, but beyond that, they still could not write the mechanism for this reaction correctly.  When a student is asked to think about the reasonableness of the mechanism, as in the mechanistically organized approach, they see that HO⁻ is not a reasonable species in an acidic medium. The mechanistic approach encourages students to develop a chemical intuition.

Another important difference in my course organized by mechanism compared to my previous functional groups course is the increased amount of time, in the former, devoted to foundational skills in the first three chapters and the emphasis on common steps between all reaction mechanisms.  In the fall semester, ODU has three sections of Organic I, but in the spring semester we have only one section of Organic II. We also have a lot of transfer students who took Organic I at other institutions. Organic II is a subject that depends heavily on the knowledge and background of Organic I so I devote my first two lectures to the topics mentioned above—foundational skills and common elementary steps in mechanisms. I need all my students to have the same starting point and understanding of expectations.

Today, I posed a question that the students will not see until later on in Organic II, but they knew the elementary step from Organic I. The majority of students were able to correctly identify the two elementary steps, though it was a mechanism they had never seen before:

Even though my large lecture classes have many challenges, the mechanistic organization helps students by teaching them to think more independently and aiding them in their problem solving approach. Students have the confidence to approach problems that they have never seen before and reason out answers.

In this way, maybe bigger is better because I’m teaching important skills to a large group of students at one time.

– Marie Melzer, Old Dominion University

Marie Melzer teaches a mechanistically organized course at Old Dominion University. She plans to use Joel Karty’s book in the fall (2014). Click here to learn more about Prof. Melzer.