Ten Essential Delocalization Learning Outcomes: How Well Are They Achieved?

Delocalization (resonance) is a concept in organic chemistry that influences the chemical reactivity, structure, and physical properties of molecules. However, the concept has proven challenging for students and the related learning outcomes had previously been only vaguely defined. We recently defined ten essential learning outcomes about delocalization that a student should be able to demonstrate by the end of a two-course organic chemistry sequence. The goal of the present study was to investigate to what extent the ten LOs were achieved by students, as well as the connections between the LOs. We analyzed three exam questions related to seven of the ten LOs for the degree of achievement, common errors, and scientific reasoning. We found that students sometimes struggled to identify when delocalization could occur, that some of the LOs built on one another, and that students were more successful in drawing resonance structures when explicitly asked, but less successful when the requirement was implicit or embedded within a mechanism. Our analysis of student reasoning showed that the dominant modes of reasoning were aligned with the related expectations and explanations in the course. When asked to justify the contribution of resonance structures to the resonance hybrid, most answers used a descriptive mode of reasoning; when asked to explain why a given proton was more acidic than another, most answers contained relational and linear causal reasoning. Implications for research and practice are discussed.