Exploring Student Thinking about Addition Reactions

Abstract

Organic chemistry is a required course sequence for many STEM students, however research indicates that organic chemistry reaction mechanisms are especially challenging for students due to a mixture of underlying conceptual difficulties, the process-oriented thinking inherent to the discipline, and the representations commonly used to depict mechanisms. While student reasoning about many of the reaction types covered in the organic chemistry curriculum have been studied previously, there is minimal research focused specifically on how students think about the mechanisms of addition reactions. This study addresses that gap by probing first semester organic chemistry students' thinking using think-aloud interviews as they worked through two different addition reactions. To elicit a range of thinking, students worked through the mechanisms using either paper and pencil or an app that dynamically represents the molecules. Overall, students were able to identify the steps of the two addition reactions but did not always successfully apply chemical thinking during the mechanistic steps. Specifically, both groups of students struggled with the concepts related to carbocation stability, frequently misapplying stabilization via substitution and demonstrating difficulty in identifying the potential for resonance stabilization. Our results suggest that instructors should emphasize the conceptual grounding directing mechanistic steps, in particular when determining carbocation stability.

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

“…One of the main representational issues reported in the literature is the alternate conception that resonance structures are alternating or in equilibrium. [2][3][4][5]8 The exam analysis could not show any indication on whether the students conceptualized that resonance structures are not real or alternating.…”

“…The answers in Question 3 that contained a reference to delocalization were mostly successful, which was also seen in a previous study. 5 However, for Question 8 half of the answers mentioning resonance were successful.…”

“…Previous work has shown that students did not frequently consider the delocalization of electrons within a mechanism. 4,5,42 LO1 (Identify) is a fundamental skill for the other LOs to be achieved in later organic problems where delocalization may not be explicitly required. Therefore, being able to determine where delocalization applies is important for learners.…”

“…The answers that invoked delocalization (Question 4: 7%, Question 6: 10%) typically had the correct answer (Question 4: 95%, Question 6: 90%), which is aligned with previous work that showed participants seem to realize that resonance was more important in determining relative stability. 4,5 Therefore, LO1 (Identify) may be a building block that helps achieve LO7 (Stability). LO8 (Acid/base): Answers included some causality and uses of strategies LO8 (Acid/base) was achieved fully by 50% of the students (Question 2).…”

“…1 Empirical studies have revealed several incorrect ideas about resonance, such as the view that resonance structures are alternating or that resonance structures exist as an equilibrium, 2,3 or may not even think to use delocalization and would have to be prompted to do so. [4][5][6][7] One intervention focused on building and exploring the representations in delocalization (i.e., hybrid and resonance structures) showed improvement in students' conceptions of the resonance structures. 8 Similarly, students taught by an instructor who focused on the meaning and limitations of resonance structures had a higher conceptual understanding of resonance compared to students in a course setting that emphasized identifying/drawing only.…”