Student conceptualizations and predictions of substitution and elimination reactions: what are they seeing on the page?

Abstract

The current study aims to contribute to the literature on how organic chemistry students weigh various factors when predicting products of substitution and elimination reactions. This study focuses specifically on these mechanism types, as they are often the first instances where students must consider the “how” and the “why” of how reactions occur. Previous literature highlights that such reasoning can be challenging. To better support our students, it is essential to understand how they conceptualize these mechanisms. Here, we present results from an investigation into how students compare bimolecular and unimolecular substitution and elimination reactions (S_N1, S_N2, E1, E2). Students completed tasks involving case comparisons and “predict-the-product” exercises. Through the analysis of nine semi-structured interviews using coordination class theory, we found that (1) students placed a greater emphasis on the importance of the starting substrate in the outcome of a reaction, and (2) focused less on the function of the nucleophile or base in each reaction. Using coordination class theory, we identified visual features and knowledge elements that students coordinated, allowing us to create “resource graphs” that represented students’ conceptualizations. These graphs helped visualize the trajectories of students’ predictions by illustrating how they balanced multiple factors. We discuss implications for supporting students in distinguishing among reaction mechanisms.