Research in organic chemistry education has revealed that students often rely on rote memorization when learning mechanisms. Not much is known about student productive resources for causal reasoning. To investigate incipient stages of student causal reasoning about single mechanistic steps of organic reactions, we developed a theoretical framework for this type of mechanistic reasoning. Inspired by mechanistic approaches from philosophy of science, primarily philosophy of organic chemistry, the framework divides reasoning about mechanisms into structural and energetic accounts as well as static and dynamic approaches to change. In qualitative interviews, undergraduate organic chemistry students were asked to think aloud about the relative activation energies of contrasting cases,i.e.two different reactants undergoing a leaving group departure step. The analysis of students’ reasoning demonstrated the applicability of the framework and expanded the framework by different levels of complexity of relations that students constructed between differences of the molecules and changes that occur in a leaving group departure. We further analyzed how students’ certainty about the relevance of their reasoning for a claim about activation energy corresponded to their static and dynamic approaches to change and how students’ success corresponded to the complexity of relations that they constructed. Our findings support the necessity for clear communication of and stronger emphasis on the fundamental basis of elementary steps in organic chemistry. Implications for teaching the structure of mechanistic reasoning in organic chemistry and for the design of mechanism tasks are discussed.

If an organic chemistry student explains that she represents a mechanistic step because “it's a productive part of the mechanism,” what meaning could the professor teaching the class attribute to this statement, what is actually communicated, and what does it mean for the student? The professor might think that the explanation is based on knowledge of equilibria of alternative steps. The professor might also assume that the student implies information about how one of the alternatives influences the energetics of subsequent steps or how subsequent steps influence the equilibria of the alternatives. Meanwhile, the student might literally mean that the step is represented simply because it leads to the product. Reasoning about energetic influences has much greater explanatory power than teleological reasoning taking the consequence of mechanistic steps as the reason for their prediction. In both cases, however, the same backward-oriented reasoning is applied. Information about subsequent parts in the mechanism is used to make a decision about prior parts. To qualitatively compare the reasoning patterns and the causality employed by students and expected by their professor, we used a mechanistic approach from philosophy of science that mirrors the directionality of a mechanism and its components: activities, entities, and their properties. Our analysis led to the identification of different reasoning patterns involving backward-oriented reasoning. Participants' use of properties gave additional insight into the students' reasoning and their professor's expectations, which supports the necessity for clear expectations in mechanistic reasoning in organic chemistry classrooms. We present a framework that offers a lens to clarify these expectations and discuss implications of the framework for improving student mechanistic reasoning in organic chemistry.

Designing problems and learning activities is a key factor to initiating students’ engagement with the course material and influencing their reasoning processes. Although tasks and problems are a central part of teaching and assessments in the chemistry classroom, they may not engage students in deep reasoning or in a way that is intended through a task. Some problems may cause an algorithmic or a surface approach. Even with designing clever problems, students may not use a larger variety of chemistry ideas and connect them in meaningful ways. Here the idea of scaffolding students’ answering process comes into play. Structuring students’ reasoning process through instructional prompts or structured worksheets supports students in activating and connecting knowledge pieces in a more meaningful way and positively slows down their fast decision-making process. This paper will discuss the importance of asking questions in chemistry teaching and highlights the idea of contrasting cases, drawn from cognitive psychology, as a task design principle. In addition to having contrasting cases as a good problem format, the idea of scaffolding students’ reasoning while solving contrasting cases through the use of instructional prompts that scaffold the reasoning process will be exemplarily showcased for mechanistic reasoning in organic chemistry.