Evaluating electrophile and nucleophile understanding: a large-scale study of learners’ explanations of reaction mechanisms

Abstract

A deep understanding of organic chemistry requires a learner to understand many concepts and have fluency with multiple skills. This understanding is particularly necessary for constructing and using mechanisms to explain chemical reactions. Electrophilicity and nucleophilicity are two fundamental concepts to learning and understanding reaction mechanisms. Prior research suggests that learners focus heavily on explicit structural features (e.g., formal charge) rather than implicit features (e.g., an open p-orbital) when identifying and describing the role of electrophiles and nucleophiles in reaction mechanisms; however, these findings come from small-scale, interview-based investigations with a limited number of reaction mechanisms. The work reported herein seeks to further explore the meaning learners ascribe to electrophiles and nucleophiles by evaluating 19 936 written explanations from constructed-response items asking what is happening in reaction mechanisms and why it happens for 85 unique reaction mechanisms across a yearlong postsecondary organic chemistry course. To analyze these data, we developed an electrophile rubric to capture learners’ level of explanation sophistication (Absent, Descriptive, Foundational, and Complex); this electrophile rubric is complementary to a nucleophile rubric previously reported in the literature. Our data show proportional levels of explanation sophistication for electrophiles and nucleophiles (τb = 0.402) across these written explanations of reaction mechanisms. We note that learners’ explanations of nucleophiles tend to be at a higher level than their explanations of electrophiles. While this finding does support prior literature reports, we also found that explanations of mechanisms involving reductions of pi-bonds (e.g., carbonyls) tended to be more sophisticated for electrophiles than for nucleophiles. Overall, our results support the claim that learners are able to discuss both electrophilicity and nucleophilicity; however, learners discuss electrophilicity and nucleophilicity at different levels of sophistication where nucleophilicity predominates for most reaction types.

Student perceptions of partial charges and nucleophilicity/electrophilicity when provided with either a bond-line, ball-and-stick, or electrostatic potential map for molecular representation

“…Results of this study informed that EPMs have affordances in cueing electron rich/poor areas within molecules that could promote students identifying electrophilic and nucleophilic characteristics and also understand the why behind mechanisms, especially nucleophilic substitution on aromatic compounds. Abstractness of organic chemistry should not be an obstacle in understanding chemical reactivity (Friesen, 2008). As EPMs make the implicit property of uneven charge distribution explicit, they are likely to offer support to students in seeing attraction between oppositely charged parts of molecules leading to leaving groups leaving, substitution occurring, or acid/base reactions.…”

Establishing a delicate balance in the relationship between artificial intelligence and authentic assessment in student learning

“…ML has also been recognised for its potential to achieve a deeper analysis of student work with recent articles published in CERP providing inspiration and guidance for teachers. Two articles that appear in this current issue include a review of studies where ML has been used to assess mechanistic reasoning in organic chemistry (Martin and Graulich, 2023) and an application of ML in assessment of student explanations (Frost et al, 2023). Rubrics and frameworks have been shared (Raker et al, 2023;Yik et al, 2023) that can be further built upon in future studies.…”

From polyphenol to o‐quinone: Occurrence, significance, and intervention strategies in foods and health implications

“…Nucleophilicity of nucleophiles has a great influence on the nucleophilic addition reaction, which refers to their relative reactivity and capability to provide an electron pair to generate new bonds with electrophiles (Frost et al., 2023). More availability of electron pairs on nucleophilic centers, such as S, O, and N, can increase the reactivity of nucleophilic species.…”