Arrows on the Page Are Not a Good Gauge: Evidence for the Importance of Causal Mechanistic Explanations about Nucleophilic Substitution in Organic Chemistry

This three-year study builds on prior work analyzing students' causal mechanistic explanations about acid-base reactions. Here we extend that work to characterize and investigate how students construct causal mechanistic explanations of simple nucleophilic substitution reactions. After an initial pilot study, we adopted a modified version of the original task prompt which was used in two subsequent years to compare responses from students enrolled in a transformed organic chemistry course (Organic Chemistry, Life, the Universe and Everything) and a traditional organic chemistry course. Student responses were sampled in the middle of the first semester organic chemistry, just after they had learned the material, and once again at the end of the course, to identify how responses changed over time. Our findings from this study include (1) eliciting causal mechanistic explanations requires careful scaffolding to activate productive elements of a response, and (2) students from a transformed course are more likely to construct a causal mechanistic explanation at the end of Organic Chemistry 2 than students from the control group, suggesting that if students are to retain the use of valuable knowledge, this must be supported by instruction and course expectations.