Applications of the Topic-Specific Pedagogical Content Knowledge Model for Teaching Electrophilic Aromatic Substitution in Organic Chemistry

Ashton B Hjerstedt, Purdue University

Abstract

Students studying organic chemistry often have difficulty applying prior knowledge from general chemistry in their thinking about organic reaction mechanisms. In the United States, electrophilic aromatic substitution (EAS) mechanisms can be taught towards the end in a secondsemester course of organic chemistry, providing students with almost two-semesters’ worth of experience with organic chemistry reactions before solving problems on synthesis of substituted aromatic compounds.Little research has been done on how, or if, instructors consider their students’ prior knowledge or understanding of these concepts in EAS in their teaching activities. The purpose of this study was to describe how students reason through EAS synthesis problems and to identify concepts or gaps in understanding that inhibit students from successfully solving these types of problems. Participants were interviewed using a think-aloud protocol in which they were asked to describe the reactants and mechanisms necessary to synthesize di- and tri-substituted benzenes using EAS. The interviews were transcribed and analyzed using a qualitative inquiry approach and the data interpreted in terms of the ACS Examinations Institute’s Anchoring Concepts Content Maps for general and organic chemistry.The findings from this study indicated that while the students correctly applied their knowledge ofsubstituent effects to solve these types of problems, they relied on rote-memorization of these effects, resulting in inflexibility when applying them to novel situations. Additionally, students exhibited gaps in understanding of fundamental concepts in resonance theory and Lewis structures, differentiating and utilizing Friedel-Crafts reactions, and recognizing when to use oxidation/reduction reactions in their syntheses.Another component of this study focused on instructors of organic chemistry from a range of institutions in the United States. The purpose of this study was to describe how organic chemistry instructors perceived their students’ reasoning about these types of problems, and to describe the characteristics of each instructor’s topic-specific pedagogical content knowledge (TSPCK) and the three general knowledge domains (GKDs) instructors draw upon to inform their TSPCK. These knowledge domains are knowledge of students, subject matter knowledge, and pedagogical knowledge. These participants were remotely-interviewed using a think-aloud protocol in which they were asked to describe their classroom practices and teaching strategies when teaching EAS, and to describe how they would synthesize the same aromatic compounds as their students (a selection of which were interviewed in the previous study). Participants were asked to consider how their students would approach the syntheses and to specify what parts of the syntheses their students would find challenging, and why. The interviews were transcribed and analyzed using a qualitative inquiry approach.The findings from this study indicated that the instructors were aware of their students’ tendencies to use rote-memorization without understanding in the course, but there was still a misalignment between how instructors’ perceived their students’ reasoning through EAS synthesis problems and the reasoning the students actually used. The instructors believed that their students would only rely on the directing effects of substituents in their reasoning, but the students demonstrated they were aware of the activating and deactivating effects too. Additionally,

Degree

Ph.D.

Advisors

Towns, Purdue University.

Subject Area

Organic chemistry|Pedagogy|Chemistry|Cognitive psychology|Curriculum development|Disability studies|Education|Higher education|Psychology|Special education

COinS