Characterizing Student Reasoning with Multiple Representations of Molecular Structure.

Organic chemistry relies on a range of symbolic representations to convey molecular structure and behavior. While each representation has specific advantages, the multitude of representations introduced is a well-documented obstacle for many students, furthered by a lack of instructional support in using the appropriate representation(s) for a given context. The contextual use of representations requires knowledge of their affordances and limitations, which is a key area of student representational reasoning that we sought to investigate. Through video-based, semistructured interviews that incorporated student annotations, we explored how 28 organic chemistry students perceive and reason about the affordances and limitations of six commonly used molecular representations: condensed structures, Lewis structures, skeletal structures, wedge-dash diagrams, Newman projections, and chair conformations. We found that most students could identify affordances but struggled to recognize limitations, with proficiency varying widely across participants. Students often relied on heuristics-based reasoning, which was productive when grounded in structural evidence and multicomponent reasoning. Those demonstrating stronger reasoning made more accurate claims, identified affordances across more conceptual categories, and articulated more relevant affordances and limitations. These findings highlight the tight interconnectedness of reasoning, conceptual understanding, and representational competence and underscore the need for instructional interventions that explicitly scaffold representational reasoning.