Exploring post-secondary chemistry instructors’ knowledge for teaching ¹H NMR spectroscopy

Abstract

Proton nuclear magnetic resonance (¹H NMR) spectroscopy is an essential characterization tool for organic chemists widely taught in the undergraduate chemistry curricula. Previous work has focused on how students advance from novice to expert in interpreting ¹H NMR spectra. However, we need to know more about how ¹H NMR spectroscopy is taught within undergraduate curricula. We sought to characterize instructors’ topic-specific pedagogical content knowledge (PCK) for teaching ¹H NMR spectroscopy as a starting point to investigate how ¹H NMR spectroscopy is taught. Participants from multiple institutions—six teaching assistants, six novice instructors, and three experienced instructors—collaboratively completed content representations (CoRes) in focus groups. Through qualitative analysis of interview transcripts and CoRes, we characterized instructors' topic-specific PCK in ¹H NMR spectral interpretation. Analysis of instructors’ responses and collective PCK elucidates the role that teaching context, experience, and disciplinary background may contribute to the character of PCK. Implications of this work include the need for research on the integration of explicit learning objectives and teaching strategies for representational competence and skills, understanding and supporting student affective experiences when learning NMR, and instructional contexts that increase autonomy in learning.

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Introduction

Spectroscopic analysis is a fundamental technique that is central to molecular characterization. Particularly, ¹H NMR spectroscopy serves as an introductory spectroscopic method that is widely included in undergraduate curricula and organic chemistry textbooks (Alexander et al., 1999; Raker and Holme, 2013; Raker et al., 2013; American Chemical Society Committee on Professional Training, 2015). Despite the technique's ubiquity and value, research has indicated developing spectral interpretation skills can be challenging for individuals (Cartrette and Bodner, 2009; Domin and Bodner, 2012; Topczewski et al., 2017; Connor et al., 2019; Stowe and Cooper, 2019), and recent research has focused on how individuals develop expertise in spectral interpretation (Connor et al., 2021a,b). In comparison, only a handful of reports focus on the teaching of spectral interpretation (Connor and Shultz, 2018; Anderson et al., 2020). Insight into how spectral interpretation of ¹H NMR spectra is taught may allow researchers and practitioners to leverage the teaching and learning of this skill in order to better support the development of student expertise. Thus, the goal of this study was to investigate what knowledge post-secondary chemistry instructors hold for teaching ¹H NMR spectroscopy to leverage what we know about the teaching and learning of this topic for future instruction.

Learning ¹H NMR spectroscopy

To interpret spectra, one must draw on chemical concepts (e.g., functional groups, molecular symmetry, and foundational physical principles of NMR) from spectral data, interpret molecular and graphical representations, and utilize successful problem-solving approaches while processing multiple pieces of spectroscopic data. In addition, ¹H NMR spectral interpretation can include the use of multiple heuristics—strategies used to decrease the cognitive load during decision-making—such as using only the ¹H NMR spectroscopy tables for determining the chemical shift of a proton or using the “N + 1 rule”, a guide to determining the multiplicity of a hydrogen peak (Shah and Oppenheimer, 2008; Connor et al., 2019). Both are rules that can become heuristics when an individual relies on the rule alone in their reasoning—one-reason decision making—without considering the conditions where they may fail to hold, which is an important yet challenging skill for novice learners.

Recent literature has focused on how students interpret and learn to interpret ¹H NMR spectra using spectroscopic data (Bodner and Domin, 2000; Cartrette and Bodner, 2009; Domin and Bodner, 2012; Topczewski et al., 2017; Connor et al., 2019; Stowe and Cooper, 2019; Connor et al., 2021a,b). Cartrette and Bodner (2009) characterized successful problem-solving approaches doctoral students utilize for interpreting NMR spectra. “Successful” solvers were consistent and organized, and they included appropriate uses of heuristics (e.g., “N + 1 rule”), a proposal of molecular structure fragments during the intermediate stage of problem-solving, and a final check of the answer. In comparison, “less successful” solvers exhibited opposite behaviors. Connor et al. (2019) explored multiple chemical assumptions—ideas about the properties of chemical entities or reactions (Maeyer and Talanquer, 2013)—and heuristics undergraduate organic chemistry students use in their problem-solving approaches during IR and ¹H NMR spectral interpretation. The authors found students hold a range of chemical assumptions, including assumptions that spectral data is “absolute” where there is little to no acceptable variation in spectral data, the “N + 1 rule” should hold, and invalid visuospatial assumptions. Additionally, students used a range of heuristics to aid in either successful or unsuccessful interpretations; most notably, students tended towards overgeneralizing learned rules or patterns without consideration of exceptions and one-reasoning decision-making based on a singular spectral feature. The authors found the use of these heuristics to be pervasive among undergraduates who struggled to interpret NMR spectral data successfully. They also found that students experienced both positive and negative emotions during interpretation, potentially impacting their problem-solving approaches.

Moreover, Connor et al. (2021a,b) mapped the development of ¹H NMR spectral interpretation expertise by comparing how doctoral and undergraduate students interpreted ¹H NMR spectra. The authors proposed that interpreters must develop a sophisticated level of understanding across five areas to develop expertise in ¹H NMR interpretation. First, interpreters must develop an understanding of foundational principles for ¹H NMR spectroscopy. Building on this foundation, development in understanding (1) deviations from the “N + 1 rule”, (2) acceptable variation in spectral data such as absorption frequency, resolution, and signal intensity, (3) visuospatial aspects of structural formulae and spectra, and (4) practical considerations such as the influence of experimental variables and acceptable variability in data are necessary for developing expertise. Instructors can use the five identified areas of expertise to inform their instruction.

Teaching ¹H NMR spectroscopy

Given the challenges faced in learning ¹H NMR spectroscopy, exploring how this subject is taught to undergraduate students is necessary. However, there is a scarcity of research on teaching college-level chemistry compared to learning chemistry (Andrews et al., 2022). At the post-secondary level, instructors begin teaching with little professional development experience, with the assumption that disciplinary knowledge makes an effective educator (Brownell and Tanner, 2012; Schussler et al., 2015). Thus, post-secondary instructors often develop their teaching knowledge through experience rather than through professional development opportunities, mentoring, or intentional reflection (Lund and Stains, 2015; Fukawa-Connelly et al., 2016; Schultz et al., 2018; Zotos et al., 2020). However, multiple studies have shown that effective evidence-based teaching requires developed teaching knowledge (Stains and Vickrey, 2017; Offerdahl et al., 2018) and content knowledge alone is not enough (Shulman, 1986; Connor and Shultz, 2018; C. Lutter et al., 2019). Researching how chemistry is taught in higher education opens opportunities for developing effective strategies for teaching challenging topics such as ¹H NMR spectroscopy while furthering theoretical understandings of post-secondary instructor development. Currently, the literature on teaching ¹H NMR spectroscopy consists of reports that focus on novel ways to teach ¹H NMR spectroscopy (e.g., Angawi, 2014; Kolonko and Kolonko, 2019; Lawson et al., 2020) and relatively few research investigations focusing on how the topic is taught (Connor and Shultz, 2018; Anderson et al., 2020). For example, Anderson et al. (2020) analyzed how organic chemistry textbooks introduce ¹H NMR spectral interpretation and scaffold worked examples and practice problems. Further, Connor and Shultz (2018) investigated graduate teaching assistants' knowledge for teaching this topic.

Knowledge of teaching chemistry. Knowledge for teaching plays an essential role in instructional practice (Shulman, 1986; Grossman, 1990; Andrews et al., 2022) and positive student outcomes (e.g., Hill et al., 2005; Sadler et al., 2013). However, research on post-secondary chemistry teaching knowledge in chemistry education in the post-secondary setting is still an emergent field (i.e., Hale et al., 2016; Connor and Shultz, 2018; Schultz et al., 2018; C. Lutter et al., 2019; Zotos et al., 2021; Boothe et al., 2023) with fewer studies centering instructors’ professional background and teaching context in the analysis of the study (Andrews et al., 2022). In one study where experience was considered, Connor and Shultz (2018) utilized a mixed methods approach to explore graduate teaching assistants' (GTAs’) knowledge of teaching ¹H NMR spectroscopy using the topic-specific pedagogical content knowledge framework (TSPCK). The authors found the GTAs’ TSPCK increased with teaching experience. Furthermore, GTAs leveraged their knowledge of learners’ prior knowledge concerning other components as well as described interactive teaching strategies (e.g., using questions to probe student understanding) over algorithmic strategies (e.g., modeling problem-solving). Further studies exploring instructional background and context in relation to knowledge development are needed (Andrews et al., 2022). Thus, this study builds beyond by including participants with a range of teaching backgrounds, including teaching assistants (TAs) and novice and experienced faculty instructors. This work aims to provide a qualitative description of post-secondary instructors' knowledge of teaching ¹H NMR spectroscopy to understand further how we teach this topic across instructional experiences and contexts with implications to improve instruction, instructor development, and further our theoretical understanding of post-secondary instructors' knowledge for teaching.

Theoretical framework

Pedagogical content knowledge

This work is guided by Shulman's seminal idea that teachers transform their subject matter knowledge and pedagogical knowledge into pedagogical content knowledge (PCK) (Shulman, 1986). Since its introduction, multiple definitions and models of PCK have been constructed (Grossman, 1990; Park and Oliver, 2008; Berry et al., 2015; Carlson and Daehler, 2019). A summit on PCK (Carlson and Daehler, 2019) divides PCK into three distinct realms: enacted PCK (ePCK); personal PCK (pPCK); and collective PCK (cPCK). We distinguish these forms of PCK similarly to Carlson and Daehler (2019), as seen in Fig. 1. ePCK is the unique individual knowledge a teacher operationalizes during lesson planning, enacting the lesson plan, and reflecting on the lesson plan. When a teacher utilizes their ePCK, they draw upon their pPCK, the personal cumulative pedagogical content knowledge held by an individual teacher in a given science discipline. Both ePCK and pPCK are deeply influenced by an individual teacher's teaching experience, the classroom environment in which they teach, and the students they teach. Reflection on teaching experience and context is vital for developing ePCK and pPCK (Shulman, 1986; Nilsson, 2008; Carlson and Daehler, 2019). cPCK is the collective professional knowledge that is held collectively among teachers and researchers in a given science discipline. When teachers and scholars share and discuss the teaching of a particular subject, they contribute to a public understanding of how that subject is taught, generating a cPCK that is held by the teachers and researchers of that subject. cPCK can build from research (known as canonical PCK) as well as extend beyond research and develop within communities of teachers and educators (Carlson and Daehler, 2019). Developing cPCK can support broader professional knowledge bases (e.g., content knowledge, knowledge of pedagogy) held by teachers and scholars (Carlson and Daehler, 2019; Boz and Belge-Can, 2020), which in turn can develop teachers’ pPCK and ePCK (Grossman, 1990; Magnusson et al., 1999; Großschedl et al., 2015). The study presented herein characterizes the cPCK developed by multiple groups of university instructors for teaching ¹H NMR spectroscopy.

Fig. 1 Illustration of the three distinct realms of PCK (cPCK, pPCK, ePCK) as inspired by Carlson and Daehler (2019).

Topic-specific PCK

For each realm of PCK, the grain size of subject matter for PCK can vary between discipline-specific (e.g., chemistry versus biology), topic-specific (e.g., spectroscopy versus electrochemistry), and content-specific (e.g., electron delocalization versus electronegativity) (Carlson and Daehler, 2019). Since this study is interested in the cPCK of a specific topic, we utilized the topic-specific PCK (TSPCK) framework defined by Mavhunga and Rollnick (2013) and Mavhunga (2019) to inform our study design and data analysis. The Mavhunga and Rollnick (2013) framework has been used to analyze chemistry instructors’ PCK for different topics such as acid–base chemistry, chemical equilibrium, electrochemical cells, and thin-layer chromatography (Mavhunga and Rollnick, 2013; Aydin et al., 2014; Hale et al., 2016; Mavhunga et al., 2016; Boothe et al., 2023) as well as GTAs' PCK for topics such as ¹H NMR spectroscopy and organic chemistry mechanisms (Connor and Shultz, 2018; Zotos et al., 2021).

Geddis (1993) first conceptualized TSPCK as “knowledge about the content that is derived from consideration of how best to teach it.” (pg. 676).Mavhunga and Rollnick's (2013) TSPCK model operationalizes Geddis’ conceptualization of TSPCK into five components (Table 1): (1) curricular saliency—knowledge of the organization of particular topics relative to the curriculum as a whole; (2) learners' prior knowledge—knowledge of students' prior knowledge and developing conceptions of a topic; (3) what makes a topic difficult to understand—knowledge of and the ability to identify “gate-keeping concepts within a topic that are difficult to understand and not necessarily misconceptions, and it triggers dedicated awareness and possible interventions for teaching them;” (Mavhunga, 2019, 132); (4) conceptual teaching strategies—knowledge of specific, effective teaching strategies that utilize conceptual principles and rules of a topic as tools for addressing learners’ developing conceptions, what makes a topic difficult, and central concepts to the topic. Conceptual teaching strategies do not include general pedagogical strategies. And (5) representations—knowledge and use of representations such as examples, illustrations, analogies, simulations, and models that are relevant to the topic (Mavhunga and Rollnick, 2013; Mavhunga et al., 2016; Mavhunga, 2019).

Table 1 Definitions of topic-specific PCK components

Component	Definition
Curricular saliency	Knowledge of the core concepts that should be taught for learning a specific topic, and the ability to identify the pre-concepts that students need to be familiar with before learning the topic.
Learners’ prior knowledge	Knowledge of students' prior knowledge to learning the topic and developing conceptions that may or may not be consistent with scientific consensus.
What makes a topic difficult to learn	An instructor's ability to identify “gate-keeping concepts'' that make learning a topic difficult for students.
Conceptual teaching strategies	Knowledge of teaching strategies that respond to an instructor's knowledge of the prior three components: curricular saliency, learners' prior knowledge, and what makes a topic difficult to understand.
Representations	Knowledge of “a range of representations including examples, illustrations, analogies, simulations, and models that are relevant to a topic” (Mavhunga, 2019, p. 132).

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The goal of this project is to provide a rich, qualitative characterization of post-secondary instructors’ TSPCK in ¹H NMR spectroscopy with the implication that the cPCK captured is informed by and can further inform instructors' personal and enacted PCK for teaching this topic. Specifically, the research question guiding this work is: What knowledge do post-secondary instructors have for teaching ¹H NMR spectroscopy?

Methods

Participants and setting

Instructors at different points in their careers and with a range of experience teaching ¹H NMR spectroscopy—six teaching assistants (TA; either undergraduate or graduate), four postdoctoral instructors, two first-year faculty instructors, and three faculty instructors with 10-plus years of experience—were recruited to describe a holistic collective PCK for this topic (Table 2). We recruited instructors from multiple institutions within the United States, including three large Midwestern research-intensive institutions and two small Midwestern primarily undergraduate institutions. Participants were selected for their experience teaching ¹H NMR spectroscopy in an introductory undergraduate organic chemistry classroom or laboratory, as this is where the topic is generally introduced to undergraduate students (Raker et al., 2013; American Chemical Society Committee on Professional Training, 2015). The TAs primarily taught ¹H NMR in individual laboratory sections of 18–20 students. The postdoctoral and novice instructors primarily taught ¹H NMR in a lecture component of a large laboratory course with opportunities to interact with students one-on-one in smaller sections led by TAs. Lastly, experienced instructors taught a mixture of both a pre-lab lecture component of a laboratory course as well as individual laboratory sections. IRB approval was obtained for this study, all participants' consent was obtained, and participants' names were replaced with pseudonyms to protect their identity.

Table 2 Participants recruited for the study, their teaching experience, and assigned groups

CoRe group	Pseudonym	Field of expertise	Teaching position	Institutional context
GTA = graduate teaching assistant; UTA = undergraduate teaching assistant; PDI = post-doctoral instructor; 1 year = instructor with one year experience as faculty instructor/lecturer; 6+ years = 6 or more years college instructional experience as faculty instructor/lecturer.
Group 1	Cecil	Materials	GTA	Large R1
	Carlos	Biological science	GTA	Large R1
	Dana	Organic	UTA	Large R1
Group 2	Maureen	Organic	UTA	Large R1
	Hiram	Organic	GTA	Large R1
	Leann	Inorganic	GTA	Large R1
Group 3	Gershwin	Analytical/chemistry education	PDI	Large R1
	Tamika	Organic	PDI	Large R1
	Steve	Organic	PDI	Large R1
Group 4	Kevin	Organic	1 year	Large R1
	Kareem	Organic	1 year	Small PUI
	Jackie	Inorganic	PDI	Large R1
Group 5	Wilson	Organic/chemistry education	6+ years	Small PUI
	Marcus	Organic	6+ years	Large R1
	Lucinda	Chemical biology/organic	6+ years	Large R1

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Data collection

To elicit and capture instructors' PCK, the authors utilized Content Representations (CoRes), a methodology developed by Loughran et al. (2004). A CoRe is a reflective tool used to capture and develop teachers’ PCK (Rollnick et al., 2008; Hume and Berry, 2011; Nilsson and Loughran, 2012; Aydin and Boz, 2013; Mavhunga and Rollnick, 2013; Schultz et al., 2018). In constructing a CoRe, teachers are tasked to fill in a matrix in which teachers identify the Big Ideas—or central concepts—of a topic and respond to provided questions (see Appendix A1) that probe the teachers’ knowledge regarding the Big Ideas and their relevance to the overarching topic. As well as what the teachers know about students learning of each Big Idea, and how they teach and assess learners for each Big Idea (Loughran et al., 2004).

Therefore, teachers' responses to a CoRe's prompts reveal a teacher's pedagogical reasoning that informs their teaching practice, encapsulating an articulated teaching knowledge (Loughran, 2019). Thus, CoRes are considered one of the most useful techniques for eliciting and capturing teachers’ PCK (Kind, 2009; Alonzo et al., 2019; Loughran, 2019).

When groups of teachers are tasked to construct a CoRe together, teachers' different and yet complementary pPCK is revealed and shaped into cPCK that can be characterized, reported, and shared with others in the discipline (Loughran et al., 2004). Therefore, the CoRe represents the collective views and knowledge for teaching a specific topic and thus represents the cPCK for the teacher group. To elicit and capture instructors' pPCK and construct cPCK for teaching ¹H NMR spectroscopy in relation to their position, instructional background, and context, we grouped participants together based on their teaching experience (Table 2). Each group was tasked to work together to construct a CoRe for teaching ¹H NMR spectroscopy to an undergraduate introductory organic chemistry class or laboratory. Video and audio recordings of the groups discussing and filling out the CoRes were captured. The audio recordings were transcribed verbatim, while the video recordings were used for context when participants used vague language or referred to the matrix.

Data analysis

The first two authors of this study (RF and EG) used provisional coding methods (Saldaña, 2021) to analyze transcripts from the focus group discussions. A codebook was constructed using the five components of topic-specific PCK—learners' prior knowledge, curricular saliency, what makes a topic easy or difficult to understand, representations and analogies, and conceptual teaching strategies—as codes (see Appendices A2, Table 6). Because the data was collected from group discussions by participants working together to fill out the CoRe, natural discussions from participants took on any number of formats, from non-verbal communication to single-line responses to multiple-sentence paragraphs. As such, the coders struggled with the “paragraph level.” Because of the unstructured nature of many of the discussions, the researchers decided to code at the utterance level, where any uninterrupted chain of dialogue from a single participant was the unit of analysis (Garrison et al., 2006).

During the first phase of coding, topic-specific codes were used, and transcripts were coded at the utterance level, where units could be assigned multiple codes. Portions of the transcripts were randomly selected for consensus coding using a random number generator. The two authors independently coded the selected portions using the initial codebook and met to discuss the coded samples and resolve discrepancies. This process allowed the authors to be familiar with the transcripts and codebook.

The authors adjusted the codebook to ensure all instructors' knowledge and experiences were captured, as well as for explicit clarity in the definitions. For example, the code definition for conceptual teaching strategies was originally pulled from the definition provided by (Mavhunga, 2019), “This code captures when instructors address knowledge of specific, effective teaching strategies that utilize conceptual principles and rules of a topic as tools for addressing learners’ alternative conceptions, what makes a topic difficult and central concepts to the topic.” While the original definition excluded generalized teaching strategies, the authors found few instances where instructors discussed teaching strategies that aligned with the codebook definition. Therefore, the authors adjusted the code to include generalized teaching strategies as well as strategies that teaching assistants observed lead instructors use to holistically capture the knowledge instructors hold for teaching strategies for ¹H NMR spectroscopy. Once the codebook was finalized, the authors relied on negotiated agreement for coding the remaining data set (Garrison et al., 2006).

During the final phase of analysis, the first author analyzed the data set by reviewing the coded CoRes and transcripts in search of themes for each component of PCK from multiple focus groups. The first author wrote reflective memos and engaged in debriefing sessions within and outside of the research team to identify emerging patterns and themes from the data set. The authors found connections between themes within each component and used existing literature to construct these themes into meaningful interpretations. The results section is organized by the five components of topic-specific PCK to provide a holistic characterization of instructors’ topic-specific PCK for teaching ¹H NMR spectroscopy.

Limitations

This study offers insight into the topic-specific PCK of instructors across teaching experiences and contexts. However, after the first round of recruitment, the majority of recruited participants were from three large research-intensive institutions. To expand teaching experiences and contexts, we conducted a second round of recruitment, but only two instructors were recruited from primarily undergraduate institutions. Since PCK is highly context-dependent, further research is needed to include instructors from different institutional contexts (e.g., primarily undergraduate institutions, community colleges), different locations (e.g., regions), and classroom settings to understand better how ¹H NMR is taught and what knowledge instructors hold for teaching this subject.

While we chose to use Loughran et al.'s (2004) CoRe for data collection, Mavhunga and Rollnick's (2013) TSPCK framework was chosen for data analysis, as this framework aligned with the goals of capturing topic-specific knowledge. Loughran et al.'s (2004) CoRe and Mavhunga and Rollnick's (2013) analytical framework overlap, but not completely. For example, instructors' knowledge of assessment is captured by prompt 9 within the CoRe, but it is not captured by the topic-specific PCK framework. Furthermore, there is no prompt that explicitly elicits instructors' knowledge of representations. While this manuscript managed to capture and report the instructors’ topic-specific knowledge for all components, this difference between our data collection tool and analytic framework may have limited findings (e.g., representations). For example, Mavhunga and Rollnick (2013) define conceptual teaching strategies as specific teaching strategies that address three other components—curricular saliency, learners’ prior knowledge, and what makes a topic difficult. However, the CoRe only prompts the instructor to report “Teaching procedures (and particular reasons for using these to engage with this idea)” with no explicit prompt to report teaching procedures in connection to prior knowledge elicited by the CoRe.

Additionally, we recognize that CoRes are limited to PCK that exists outside of classroom practice. While we designed data collection to include group discussion to capture cPCK it also provided a vehicle to make participants’ tacit knowledge explicit when filling out the CoRe together. However, the use of CoRes and captured discussions as sole data sources may not capture instructors’ knowledge that is enacted in the classroom, nor does it indicate the quality of instruction. We hope that future research can complement these findings by investigating enacted topic-specific PCK through the use of observations, interviews, and CoRes or other methods. This recommendation aligns with previous findings that demonstrate the need for research on enacted PCK in the classroom (Alonzo et al., 2019; Andrews et al., 2022).

Results & discussion

Curricular saliency

Curricular saliency is the knowledge of the core concepts that should be taught for learning a specific topic, and the ability to identify the pre-concepts that students need to be familiar with before learning the topic (Mavhunga, 2019). Questions 1, 2, and 3 from the CoRe (see Appendix A1) were used to identify the pre-concepts that participants determined should be taught for ¹H NMR spectroscopy. The Big Ideas described by participating instructors were used to identify the core concepts that they thought should be taught for learning ¹H NMR spectroscopy. We identified differences in the Big Ideas proposed between groups (see Appendices A3, Table 7 for all Big Ideas proposed by instructors).

The Big Ideas were first compared across groups. Different groups identified similar Big Ideas with different titles, thus, we collapsed similar Big Ideas together. For example, the Big Ideas “Understanding NMR as a puzzle/protocol” (Group 1), “Proposing/confirming molecule via spectrum” (Group 3), “Fragments and Degrees of Unsaturation” (Group 4), “Integrated spectroscopy to identify unknowns”, and “Using¹H NMR to evaluate the progress of a chemical reaction” (Group 5) were Big Ideas that characterized teaching students how to approach ¹H NMR spectral interpretation, thus these ideas were collapsed down to one Big Idea by the authors, “¹H NMR Spectral Interpretation.” A summary of the pre-concepts and core concepts for ¹H NMR spectroscopy are shown in Table 3. Instructors discussed three pre-concepts that students should be familiar with prior to learning ¹H NMR spectroscopy in their classrooms. Instructors identified that students should be familiar with: (1) IR spectroscopy and its underlying chemical and physical principles; (2) fundamental organic chemistry concepts such as electronegativity and resonance; and (3) being able to understand and use representations of molecules such as Lewis structures and 3D models.

Table 3 Summary of curricular saliency results including pre-concepts and Big Ideas

Pre-concepts
IR spectroscopy	Students should be familiar with how to analyze an IR spectrum and understand the underlying physical and chemical principles of the instrument.
Fundamental organic chemistry principles	Students should be familiar with fundamental organic chemistry principles typically introduced or expanded upon in an introductory Organic Chemistry lecture, such as electronegativity and electron delocalization.
Representations	Students should be able to understand and effectively use representations of molecules such as Lewis structures and 3D models.
Big ideas
Defining spectroscopy	Students should be able to describe what ^1H NMR spectroscopy is and its applications across disciplines.
Understanding the instrument	Students should be familiar with the fundamental physical principles behind a ^1H NMR spectrometer and what gives rise to spectra. Potential sub-concepts can include light-matter interactions and magnetism.
Equivalency	Students should be able to understand how topicity and symmetry give rise to the Big Ideas of Chemical Shift, Multiplicity and Splitting, and Integration.
Chemical shift	Students should be able to use the chemical shift of peaks to identify potential proton environments of an unknown molecule.
Multiplicity and splitting	Students should be able to identify split peaks. Students should be able to use peak multiplicity to identify the connectivity of surrounding proton environments of an unknown molecule. Students should be able to calculate the number of protons in neighboring environments using the n + 1 rule.
Integration	Students should be able to use integration to determine the number of protons associated with each peak and proton environment of an unknown molecule. Students should be able to reduce ratios of integration.
Laboratory skills	Students should demonstrate the appropriate laboratory skills needed to obtain a ^1H NMR spectrum. Laboratory skills can include determining appropriate deuterated NMR solvents, demonstrating sample preparation, and running the instrument.
^1H NMR spectral interpretation	Students should be able to apply Big Ideas 2–6 and utilize successful problem-solving approaches for ^1H NMR interpretation of an unknown molecule.

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Instructors considered the four spectral features—equivalency, chemical shift, multiplicity and splitting, and integration—foremost when discussing the CoRe. All groups discussed all four spectral features while filling out the CoRe. However, Group 3 and 5 were the only groups to identify all four spectral features among their Big Ideas on their CoRes. In contrast, Groups 1, 2, and 4 discussed the concept of equivalency in relation to other Big Ideas, such as splitting (Groups 1 and 2) or molecular symmetry (Group 4). These four spectral features are consistent with previous studies on how textbooks teach NMR (Anderson et al., 2020) and on student learning of NMR (Connor et al., 2019).

Groups, which were organized by relative teaching experience, were not uniform in their description of Big Ideas. For example, the experienced instructors in Group 5 connect the concept of equivalency to how the instrument produces unique signals and how to interpret these signals on a spectrum to identify unique hydrogen environments by separating equivalency into two big ideas: “Big Idea “A”: NMR Fundamental Theory – Hydrogens in different environments interact with radio photons differently,” and “Big Idea “B”: With respect to symmetry, unique hydrogens can be identified by independent signals/peaks/resonances.” While de-emphasizing the need for students to understand the underlying physical chemistry that gives rise to spectroscopic signals, the experienced instructors centered equivalency around the purpose of NMR as identifying the active nuclei of interest (e.g., hydrogens) and its connectivity to other unique hydrogen groups.

Group 4, which included three novice faculty instructors, emphasized equivalency's connection to symmetry and its consequences on the four spectral features. Jackie, an inorganic researcher, and organic chemistry laboratory instructor, first introduces the concept of symmetry as a Big Idea to their group by reflecting on learning about symmetry in their undergraduate organic and inorganic classes:

“I think that's, for me, those were always one of the almost like the failures of the way I thought NMR Spectroscopy was taught and that […] when I was taught it […] Just like symmetry that you learn with either your character tables or your flow charts in inorganic class, […] it's the same exact thing for an organic molecule and how you go about assigning NMRs. But kind of the way those topics are taught, it just came off as two completely different topics.” (Jackie, Novice)

Jackie's experience as an inorganic student, an inorganic researcher, and reflections on teaching ¹H NMR spectroscopy may have led Jackie to propose molecular symmetry as a Big Idea rather than equivalency. Through discussion, members of his group agreed to add the Big Idea of symmetry with equivalency included as a sub-concept. Prior experiences and content knowledge play a large role in PCK development (Grossman, 1990; Davidowitz and Potgieter, 2016; Connor and Shultz, 2018). Other research reports that experienced doctoral students and researchers pull on their research and academic experience for successful spectral interpretation (Cartrette and Bodner, 2009; Connor et al., 2021a). Thus, the differences observed with our participants may be attributed to their different disciplinary research experiences (Cartrette and Bodner, 2009; Connor et al., 2021a) and varying levels of PCK (Grossman, 1990; Davidowitz and Potgieter, 2016).

In contrast, Groups 1 and 2, which included participants who were undergraduate and graduate student teaching assistants and had less experience teaching NMR, described equivalency as a sub-concept that gives rise to other Big Ideas, specifically multiplicity, and splitting, instead of being its own Big Idea. During the discussion, the TAs drew upon their own teaching experiences and their experiences as students learning ¹H NMR spectroscopy. This difference in curricular saliency in contrast to the more experienced instructors may arise from the TAs' level of content knowledge and curricular knowledge. Curricular saliency requires both advanced content knowledge of organic chemistry and institutional knowledge of the curriculum (Davidowitz and Potgieter, 2016; Mavhunga et al., 2016). Zotos et al. (2021) found their GTA participants held differing levels of curricular saliency from each other and faculty participants for teaching organic chemistry mechanisms. The authors proposed these differences may arise from GTAs’ differing undergraduate experiences as well as limited opportunities to critically reflect on broader curricular knowledge, such as providing input on course curricula or learning about the overall departmental curriculum. There were no other notable differences across groups.

The inclusion of the Big Ideas Defining Spectroscopy, Understanding the Instrument, Laboratory Skills, and Spectral Interpretation across most groups denotes the importance of hands-on experience for learning scientific practices and obtaining disciplinary knowledge among the instructors. Big Ideas such as Defining Spectroscopy and Understanding the Instrument intend for students to understand how organic chemists acquire information about molecular structures, and Laboratory Skills and Spectral Interpretation aim to promote laboratory skills and techniques that aid in acquiring chemical knowledge through experimentation. This finding is unsurprising since all instructors teach within the context of a laboratory course—either as a laboratory instructor and/or lecturer for a laboratory course—and ¹H NMR spectroscopy is typically taught in or alongside laboratory courses. Additionally, these Big Ideas align with the ACS's learning objectives for teaching the application of topics and developing laboratory skills and analysis (Committee on Professional Training, 2015; Connor and Raker, 2022).

Instructors' responses and CoRes highlighted how their range of research, teaching, and student experiences, as well as teaching context, play a role in what they consider important to teach. The results outlined here indicate the importance of instructor context and experiences in their curricular saliency development, supporting our existing theoretical understanding of this component.

Learners’ prior knowledge

Learners’ prior knowledge refers to instructors' knowledge of the prior knowledge students hold when learning the topic and includes students' developing conceptions of the topic. Here, we define developing conceptions as conceptions that may or may not be productive for students learning a topic. Discussions of students’ prior knowledge arose during instructors’ discussion of Questions 5–7 of the CoRe. Instructors reported on multiple developing conceptions of students’ prior knowledge of general concepts such as students' understanding of fundamental organic chemistry concepts, prior knowledge of other spectroscopic techniques, and students’ skill in using molecular representations. Instructors also reported on three specific unproductive developing conceptions students may hold; these conceptions were (1) interpreting peak height instead of area for integration, (2) interpreting overlapped peaks as split peaks, and (3) considering hydrogens in the same functional groups as equivalent. We did not notice differences in responses regarding learners’ prior knowledge between groups. A summary of general and specific developing conceptions is reported with sample responses and is included in Table 4.

Table 4 Summary of instructors’ knowledge of learners' prior knowledge and developing conceptions when teaching ¹H NMR spectroscopy

Learners’ prior knowledge	Description	Sample response
General developing conceptions
Fundamental organic chemistry concepts	Students have a developing and inconsistent understanding of fundamental Organic Chemistry concepts.	“When they start getting into the exceptions, the fundamental understanding is not present.” (Cecil, TA)
Experimental and spectroscopic techniques	Students have a range of prior knowledge and experiences with other experimental and spectroscopic techniques such as TLC, IR, MRIs, etc.	“I guess that's another issue that would probably go on the previous column, that a lot of them think IR isn't more reliable and less ambiguous method than NMR because it's taught to them first. You're like, “Oh no, IR can tell you anything because it's so ambiguous.” (Cecil, TA)
Two-dimensional to three-dimensional visualization	Students are still developing the skill to translate two-dimensional representations of molecules (i.e., Lewis structures) to a three-dimensional visualization.	Cecil: “I think it's difficult for most people to understand symmetry. Especially three-dimensional.” Carlos: “Yeah, the symmetric is very complicated. […] It is hard to visualize.” (Cecil and Carlos, TA)
Specific, unproductive developing conceptions
Peak height indicates integration	Students may hold the conception that peak height is an indicator of integration.	“Well, I mean, they are totally fooled by shapes of peaks. […] I think they almost correlate automatically height to area.” (Lucinda, Experienced)
Overlapped peaks indicate multiplicity	Students may hold the conception that some overlapped peaks indicate multiplicity.	“Because they don't find it easy to distinguish a splitting or multiplicity from peaks that are close to each other, which is also correlated to shift issues.” (Lucinda, Experienced)
Equivalency	Students may hold the conception that hydrogens in the same functional groups are equivalent hydrogens.	“Some people would be like, ‘Oh, there's only two protons on this carbon, so why is it a singlet?’ Not understanding, or misconceptions between protons in the same electronic environment versus neighboring protons.” (Leann, TA)
Representational competence	Set of skills and practices that allow one to effectively interpret, use, and communicate with representations of chemical phenomena and underlying physical and chemical properties.	“They just don't understand that it is a way to see a molecule. Something about that is meaning the molecule and they I mean, that's the same reason that they don't understand things like equivalence. They don't, it's just a drawing on paper. They don't take it to the next level of actually giving it an identity and a uniqueness and then what do I do about quantities?” (Lucinda, Experienced)

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An underlying theme across instructors' reports on students’ developing conceptions is students' ability to interpret concepts from, translate between, and use molecular representations. For example, Cecil described their students as still developing an understanding of electron delocalization and ability to identify electron withdrawing and donating functional groups from molecular representations, “A lot of students don't have a foundation in electron withdrawing or electron donating functional groups.” In a discussion about difficulties in teaching symmetry, Kareem, a novice instructor in Group 4, described chirality as a topic that students continually struggle with prior to learning NMR. Lastly, instructors explicitly described students' ability to understand molecular representations two-dimensionally and three-dimensionally. For example, Jackie reports on students having varying abilities to translate 2D representations, “Just translating from a flat chalkboard to a three-dimensional structure, I feel like it takes different students vastly different amounts of time to finally start to visualize stuff […] I think all of us [expert instructors], we can see a molecule and we can just spin it in our head probably, and that is certainly not something an undergrad can usually do.” (Jackie, Novice)

Lucinda takes it a step further by connecting students’ developing ability with representations and spatial arrangement to their developing conceptions about equivalency and multiplicity, “I think for me, I know that students have a very unclear idea of what connectivity is and spatial arrangement. […] They lump them as groups, and then we probably do part of the damage because we always refer to functional groups and things, but they don't then have a clear idea of exactly what's attached to what. It's just groups of things. […] Three hydrogens attached to the same carbon, a methyl group, they have only a very vague idea that those hydrogens are attached to the carbon they think of it like a methyl group.” (Lucinda, Experienced).

Instructors' conceptions of students’ developing understanding of fundamental organic chemistry concepts align with chemistry education literature on students’ conceptions (Coll and Treagust, 2002; Bhattacharyya and Bodner, 2005; Anderson and Bodner, 2008; Cartrette and Mayo, 2011; Anzovino and Bretz, 2015; Petterson et al., 2020; Brandfonbrener et al., 2021).

For example, Popova and Bretz (2018c) found many of their organic chemistry students encountered challenges when connecting chemical concepts (i.e., activation energy or reaction progress) to surface-level features (i.e., peak height and width) of reaction coordinate diagrams. ¹H NMR spectral interpretation requires sufficient understanding and application of fundamental organic chemistry concepts and may require additional instructional effort due to its complexities (Connor et al., 2019; Connor et al., 2021a). However, the literature related to instruction of NMR only contains instructors' discussion of students' unproductive developing conception of splitting, with no focus on how instruction influences students’ knowledge, application, and transfer of underlying organic chemistry concepts in learning ¹H NMR (Connor et al., 2019). Here we see the instructional influence pulled through in Lucinda's report that the way instructors present topics to students may introduce an unproductive conception of grouping. This result highlights the importance of investigating both instructors' and students’ perceptions of teaching and learning of a particular topic to give a more holistic understanding. Understanding how developing conceptions are introduced and reinforced during instruction and individual student learning can aid in the development and practice of instructional interventions.

Instructors’ reports on students' developing skills with molecular representations and unproductive developing conceptions about peak height and identifying equivalent hydrogens may be connected to representational competence and skill. Recent literature has focused on supporting students' skills and competence of interpreting structural representations of molecules (Keig and Rubba, 1993; Kozma, 2003; Goodwin, 2008; M. Strickland et al., 2010; Harle and Towns, 2011; Popova and Bretz, 2018a,b; Zotos et al. 2021; Gurung et al. 2022). For example, Popova and Bretz (2018b) found that undergraduate students struggled to identify and interpret reaction coordinate diagrams and other mechanistic representations, which led to unproductive developing conceptions when moving between reaction mechanisms and reaction coordinate diagrams. These findings parallel instructors' reports on students' challenges in connecting chemical concepts to molecular representations and spectroscopic features. While post-secondary chemistry instructors’ objectives and teaching of representation competence and skills have been studied (Popova and Jones, 2021; Jones et al., 2022), instructors’ PCK for developing students’ representational competence has not been explored in the literature. Further research is needed to understand what knowledge chemistry instructors hold about chemistry students’ developing representational competence and skills.

What makes a topic difficult

“What makes a topic difficult to understand” refers to the instructor's ability to identify “gate-keeping concepts'' and skills that make a topic difficult for students to learn and instructors to teach (Mavhunga, 2019). Skills were included with this definition since laboratory and interpretation skills were among the Big Ideas included across groups. Discussions of these gate-keeping concepts arose during instructors’ discussion of Questions 5–7 of the CoRe. We identified three aspects of ¹H NMR spectroscopy that make the topic difficult to understand from the instructors' discussions: (a) ¹H NMR spectroscopy is “abstract” to students, (b) chemistry vocabulary is a barrier to learning ¹H NMR spectral interpretation, and (c) spectral interpretation is a developing skill. We did not notice differences in knowledge on “What makes a topic difficult” between groups.

Instructors perceived concepts such as electron delocalization and magnetism as barriers to learning ¹H NMR spectroscopy due to their being “abstract” concepts. For example, Dana, a GTA, reasoned that electron delocalization in itself is abstract to their students, which acts as a barrier to understanding how the chemical shift of a proton is influenced by the surrounding electrons.

“It's hard to get the concept. I get, it's the stretching of the absorption, but then NMR, it's like almost too abstract and trying to get them to understand the electronics of it is hard when they don't have a strong understanding of electrons.” (Dana, TA)

Furthermore, instructors found ¹H NMR's abstract concepts challenging to teach due to perceived limited relevant analogs or analogies for instructors to operationalize. For example, a novice instructor, Kevin, identified the underlying physical principles of the instrument, such as magnetism and spin states, as difficult concepts to teach students due to those concepts having no perceived relevant analog to students,

“I think what popped into my mind first is very similar, but just that magnetism is like really abstract. It's like really hard to put into terms of something on a daily basis that you encounter on a daily basis. […] I feel like [the spring model of IR is] intuitive, but magnetism it's like almost like this binary language…” (Kevin, Novice).

Experienced instructors perceived the impacts on students’ affect due to their experiences with abstract concepts. For example, Wilson found that the underlying physical chemistry concepts' close relationship to physics and calculus “frightens” students which can limit students’ motivation to understand these concepts.

Within and across groups, instructors discussed similar experiences with students' understanding of chemistry vocabulary, such as shielding and deshielding. For example, Tamika, a postdoctoral instructor from a novice group, comments on how using “jargon” when first teaching the topic is “confusing” for students:

“I don't know where to put this, but the terminology, upfield, downfield, seems like it's confusing, and I think realizing that they can't overuse that jargon in the beginning.” (Tamika, Novice).

Instructors reported that their students—and they themselves—commonly mix up vocabulary, such as shielding versus deshielding and upfield versus downfield. Particularly, the teaching assistant groups (Groups 1 and 2) discussed inconsistencies in the use of vocabulary among teaching assistants and students outside of the classroom causing confusion for students who interacted with other teaching assistants or students outside of the classroom.

Lastly, we identified spectral interpretation as a difficult skill for students to develop from instructor discussions. Across groups, instructors noted students engaged in multiple spurious chemical assumptions and heuristics in their problem-solving approaches. For example, instructors noticed students may over-rely on heuristics such as the chemical shift tables that students are provided to help determine which proton environments are present in a molecule. An experienced instructor felt this overreliance leads to some students not considering how topicity and delocalization influence where the proton signal may fall on the chemical shift axis.

“I was thinking: one of the ones that always jumps out at me as well, “I saw this peak at 4.5 ppm, but we don't have a double bond in our structure. So, I guess, blah, blah, blah”. And I'm just like, be flexible enough that you can think about additivity. […] I mean, once they get a handout or something, you know, with all the zones written down, it's like, that's gospel.” (Wilson, Experienced)

Instructors presumed students' over-reliance on the chemical shift tables was due to their students’ holding assumptions that data from obtained spectra and reference materials provided are objective and absolute where there is little to no acceptable variation in spectral data. Instructors described students expecting spectral data to be clean or “perfect.” For example, Dana described her experience of her students questioning the identification of a proton because the chemical shift does not lie exactly in a range that is on the spectroscopy table: “On the basis of chemical shifts, they can think very concretely. […] they look at the table, and they're like, if it's not at 3.8 then this isn't it?” (Dana, TA).

Moreover, Lucinda, an experienced instructor, noticed their students' assumptions of experimental data being absolute and their reliance on the chemical shift tables can lead to engaging in one-reason decision making, which could lead to incorrect interpretations of the spectrum:

“They want to rigidly adhere to [the chemical shift tables], if it's supposed to be between three and four, then no matter what my compound might have in it, I know that it has to have that.” (Lucinda, Experienced)

Furthermore, experienced instructors wrote in their CoRe about the difficulties in “Challenging students to move beyond a rigid, purely electronegativity-based analysis” and instead encouraged students to consider structural features such as bonding and symmetrical elements.

Instructors identified multiple areas of what makes a topic difficult to learn, some of which have been explored and studied in education literature. Abstract and complex concepts are often cited as a barrier to learning chemistry, leading to students developing unproductive conceptions (Bhattacharyya, 2008; Alvarado et al., 2015). As Kevin, a novice instructor, said, students and instructors may perceive a lack of transfer or relevance in learning these abstract concepts, which may affect student motivation and meaningful learning for ¹H NMR spectroscopy. Additionally, the language of chemistry has been found to be a barrier for students (Bowen et al., 1999; Pyburn et al., 2013; Markic and Childs, 2016; Connor et al., 2019; Quílez, 2019; Connor et al., 2021b). Learning the language of chemistry, including vocabulary, is essential for engaging in scientific discipline and practice. However, students have been found to equate terms with different meanings (Alvarado et al., 2015; Popova and Bretz, 2018a; Quílez, 2019) which in turn can limit students learning, problem-solving and interpretation abilities (Bowen et al., 1999; Bhattacharyya and Bodner, 2005; Pyburn et al., 2013; Haglund et al., 2015; Popova and Bretz, 2018b; Quílez, 2019).

Lastly, instructors identified their students holding incorrect chemical assumptions that experimental data is absolute, leading to misuse of heuristics, as an aspect that makes the topic difficult to learn. Evidence of students' assumptions that data is absolute has been seen in the literature (e.g., Alvarado et al., 2015; Connor et al., 2019) and has been connected to students' ability to consider multiple chemical properties (e.g., Tümay, 2016) and constrains students problem-solving approaches to spectral interpretation (Connor et al., 2019). Connor et al. (2019) describe undergraduate students overgeneralizing multiple heuristics such as spectroscopy tables and the “N + 1 rule” during interpretation tasks. Instructors' observations of students' affect and perceptions about spectral data reflect Grove and Bretz's (2010) finding that undergraduate students expect organic chemistry to be “straightforward” and “objective.” Students’ assumptions may lead to negative affective experiences and pose as a barrier to student learning thus, instructors should consider how to facilitate conversations and use instructional strategies for teaching students to interpret acceptable variety in experimental data and appropriately use heuristics such as the spectroscopy tables.

Conceptual teaching strategies

Mavhunga defines conceptual teaching strategies as knowledge of teaching strategies that respond to an instructor's knowledge of the prior three components: curricular saliency, learners' prior knowledge, and what makes a topic difficult to understand (Mavhunga et al., 2016; Mavhunga, 2019, p. 4). We analyzed instructors’ responses to Questions 7 and 8 for conceptual teaching strategies in response to these components. We organized the strategies into several broad categories and herein report on several types of conceptual strategies proposed by the instructors for each component. Overall, groups conveyed conceptual strategies that rely on knowledge-telling, demonstrating, and reinforcing algorithmic problem-solving approaches. There was an absence of strategies that address unproductive developing conceptions. In addition, instructors' strategies included addressing student affective states through knowledge-telling, using active strategies such as providing practice problems or posing questions to students, and providing or utilizing online curricular resources to students. Furthermore, we identified differences in types of teaching strategies between groups. A summary of proposed conceptual teaching strategies for each component is provided in Table 5.

Table 5 Summary of conceptual teaching strategies for ¹H NMR spectroscopy

Strategy type	Knowledge telling strategies	Active strategies
General strategies	Present and review content.	Practice interpreting spectra or specific spectral features.
	Explain concepts to students.
	Work practice problems to demonstrate interpretation.
	Show example spectra to demonstrate concepts and/or interpretation.
	Use physical or digital models for molecular structure visualization.
Concept-specific strategies
Defining spectroscopy	Connect to real-world examples (e.g., MRI).
	Leverage prior knowledge of IR.
	Present concepts simply.
Understanding the instrument	Use props for light–matter interaction.
	Show videos/drawing/simulations.
	Connect to real-world examples (e.g., MRI).
	Present concepts simply.
	Show example spectra to demonstrate the influence of magnet strength on splitting.
Laboratory skills		Practice obtaining spectra in the laboratory, running reactions, and obtaining samples.
^1H NMR spectra interpretation	Present a process or step-by-step procedure.	Provide ^1H NMR and IR spectra for students to practice interpreting.
	Work example problems for demonstration.
	Direct students to work together in small groups.
Abstract concepts	Show video or simulations to understand abstract physical chemistry concepts.
	Present concepts simply.
Difficulties in interpretation	Direct students to work in groups.	Pose questions to students to scaffold their problem solving.
	Tell students to not over-rely on the spectroscopy table.	Provide problems or spectra for students to practice interpretation.
	Reassure students to address student affect.
	Explain to students “to be flexible” or “no right or wrong answer”.
	Demonstrate interpretation with examples or procedures.
	Present step-by-step procedure.
	Use ChemDraw to demonstrate topicity on chemical shift.

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Of the strategies reported for teaching across the Big Ideas, the most common strategies proposed by the instructors across groups were knowledge-telling strategies. Knowledge-telling strategies are characterized by the instructor proposing to deliver content, information, or directions to students in the laboratory or classroom either directly to a student or in a lecture format. For example, the experienced instructor group noted they would cover their Big Idea “A”: “The Fundamental Theory of NMR” in a primarily “lecture-based” format. Furthermore, instructors across groups identified areas where they needed to “explain” or “tell” information to their students more directly. For example, when answering Question 8 for their Big Ideas on chemical shift, integration, and splitting, TA Group 2 listed, “explaining how to approach problems – Explaining to them how to use the information learned in lecture to apply toward solving problems” as the primary strategies for addressing these CoRe concepts.

Outside of knowledge-telling strategies, all instructors emphasized the importance of students practicing interpreting ¹H NMR spectra and individual spectral features (e.g., peak position, peak area, multiplicity). Specific teaching strategies for promoting students’ interpretation included demonstrating how to interpret either individual features (i.e., chemical shift) or an entire NMR spectrum, providing students with a step-by-step procedure for interpreting spectral features, providing problems that task students to interpret example spectra of known molecules and predict spectral features in practice problems.

Teaching strategies for addressing Learners’ Prior Knowledge included reviewing fundamental organic chemistry concepts to address inconsistencies in introductory organic chemistry concepts and using or providing models to students to aid visual representations of molecules. None of the instructors offered conceptual teaching strategies to address unproductive developing conceptions about spectral features for chemical shift, integration, and multiplicity.

To address the three characteristics that make learning ¹H NMR difficult to learn, instructors proposed using videos or simulations to help students understand certain abstract concepts such as electron density or attempting to “keep it simple” by reducing the amount of detail provided when lecturing on concepts. For chemistry vocabulary as a barrier to student learning, instructors identified no specific strategy other than stating they expect students to memorize terms related to NMR.

One strategy proposed for addressing difficulties in teaching spectral interpretation included responding to students' affective moments when interpreting ¹H NMR spectra. For example, some instructors noted when students obtained authentic spectra from the laboratory or encountered “imperfect” spectra in a problem, it created discomfort or uncertainty for their students. In response to a discussion about students encountering authentic spectra in the laboratory, Wilson said,

“[I am] fascinated by the students just, they're not just uncomfortable with me not knowing what's going to happen, they abhor it.” (Wilson, Experienced)

Cecil reasoned their students may have negative experiences because they prefer to have a final correct answer they can check,

“I think that would build a lot of students' confidence because right now they try and check their work against something and can't.” (Cecil, TA)

Instructors attempted to alleviate these affective experiences in a variety of ways. Wilson and other instructors proposed knowledge-telling strategies to build student confidence in the laboratory environment. For example, Lucinda explains to her students that there are no right answers, and that further information may be needed as a way to “reassure” her students.

“That's what I try to make my students understand too, it's reassuring to know that there can be more information coming and there can be more ways to interpret. You know, it's better for them than thinking: ‘There's got to be the right answer. And if I don't get the right answer, then I'll be marked down’.” (Lucinda, Experienced)

Additionally, Cecil directs students to an online spectra database for students to confirm their interpretations as a way to build confidence.

Similarly, instructors proposed a variety of strategies for addressing students' assumptions with respect to absolute data. Some instructors explained they would tell students that spectral data is not absolute; the data may not match a spectroscopy table due to other molecular features introducing variation into the spectral data. They described telling students to be “flexible” when interpreting and would demonstrate how they interpret chemical shifts. Some instructors reported posing scaffolded questions to guide students’ reasoning during one-on-one interactions. For example, Leann, a teaching assistant, reasoned their students were oriented to finding a “final answer” and therefore were reliant on the spectroscopy table to get to that answer. Therefore, Leann and other instructors use posing scaffolded questions to guide students' reasoning in one-on-one teacher–student interactions to orient students to “processing [the spectral data] for themselves”. Specifically, Leann described how she likes to ask her students to predict spectral features from the molecule,

“I said, ‘Okay, here's a molecule, […] Where do you think the [hydrogens] should be?’ Or ‘Here's a spectrum, give me a range, give me what you think these particular groups are. Let's build a possible molecule out of it.’ […] I like to ask questions and get responses to questions.” (Leann, TA)

Lastly, Lucinda proposed using ChemDraw as a tool for students to practice predicting chemical shifts of protons for known molecules:

“I would have them use something like ChemDraw with its interactive [spectrum]. […] I think the interaction really actually [helps students] to click with it. If they can scroll over something and see it highlighted. It helps a ton.” (Lucinda, Experienced)

Lucinda provided the reasoning that the interactive features of ChemDraw allow students to see tangible connections between the chemical shift and molecular structure to reduce students’ assumptions about spectral data being absolute.

Additional strategies reported included using either physical or simulation models to aid in visualizing molecular structures for Spectral Interpretation and Understanding the Instrument, practicing laboratory skills for Laboratory Skills, and directing students to work together when practicing Spectral Interpretation.

In all, instructors reported mostly knowledge-telling strategies when introducing content and building upon students’ affective experiences. Instructors only rarely reported using active strategies such as posing questions to students or providing practice problems for introducing concepts. This is unsurprising as knowledge-telling strategies such as delivering content in a lecture format are ubiquitous in higher education (Raker and Holme, 2013; Stains et al., 2018) and for teaching spectroscopy in lecture and laboratory settings (Alexander et al., 1999). Furthermore, Zotos et al. (2021) found that knowledge-telling strategies were the most common teaching strategies provided when GTA participants assessed authentic undergraduate responses on an organic chemistry mechanism exam question. However, the proposed knowledge-telling strategies on their own may fail in addressing this area as knowledge-telling strategies on their own are ineffective in promoting conceptual understanding (Bodner, 1986). Instead, the majority of approaches proposed could reinforce algorithmic approaches instead of problem-solving approaches that rely on students drawing on their conceptual understanding of chemical principles and spectral features in order to interpret spectra (Bodner, 1986; Bhattacharyya and Bodner, 2005; Cartrette and Bodner, 2009).

Additionally, instructors rarely provided further context on how they would help facilitate student learning while practicing interpretation beyond selecting and providing practice problems to students. This finding is in contrast to Connor and Shultz's (2018) finding their GTAs were less reliant on algorithmic teaching strategies and reported interactive strategies when teaching ¹H NMR spectroscopy. This may be due to GTAs’ unique position to undergraduate students where GTAs are more likely to have one-on-one interactions with students in comparison to lead instructors of large courses (Zotos et al., 2020, 2021). Indeed, instructors who reported posing questions to students (e.g., probing questions or scaffolding questions) in this study were all teaching assistants for an organic chemistry laboratory. This is in contrast to the experienced instructors who reported less on their one-on-one student interactions potentially due to teaching large lecture components of the laboratory, who focused on more curricular objectives, choosing problems, and assessments rather than in-the-moment teaching practices.

As stated prior, PCK develops with experience and reflection on teaching (Lederman and Gess-Newsome, 1999; Davis and Krajcik, 2005; Hale et al., 2016; Carlson and Daehler, 2019). Moreover, it has been reported that conceptual teaching strategies is the most difficult component to develop for PCK as it relies on the instructor to have sufficient pedagogical knowledge and knowledge of other topic-specific PCK components (Zotos et al., 2021; Andrews et al., 2022; Schultz et al., 2022). It is reported that teachers often rely on algorithmic approaches for problem-solving instead of conceptual understanding across chemistry concepts such as the mole (Rollnick et al., 2008), stoichiometry (Malcolm, 2015), and acid–base chemistry (Tümay, 2016; Boothe et al., 2023). Given the literature on instructor reliance on approaches that may reinforce algorithmic approaches, we identified that this may be exacerbated by the lack of proposed topic-specific strategies for navigating students' developing conceptions in problem-solving as well as facilitating student thinking during interpretation. A further need to introduce structures for sharing teaching strategies and PCK development is emphasized.

Representations

Mavhunga defines the component of representations as the knowledge of “a range of representations including examples, illustrations, analogies, simulations, and models that are relevant to a topic” (Mavhunga, 2019, 132). Instructors discussed representations during Questions 6–8. Instructors identified several methods for representing molecules, general spectral examples, and analogies they leverage when teaching. We did not notice differences in instructors’ knowledge of representations between groups.

Instructors discussed using different ways to represent molecules when teaching ¹H NMR spectroscopy. The most common representations reported included two-dimensional Lewis dot structures, wedge-and-dash projections, and three-dimensional ball-and-stick models. Instructors reported using software such as ChemDraw for creating two-dimensional representations of molecules and using three-dimensional model kits or software such as Spartan for three-dimensional models. These representations were often used to instruct students about the influence of molecular features and structure on Big Ideas such as equivalency, multiplicity, and other spectral features.

Similarly, some instructors established the use of example spectra as essential to teaching individual spectral features such as chemical shift. For example, Dana, a TA, suggested using example spectra to demonstrate when signals may fall outside of the ranges that is reported in a spectroscopy table,

“I feel this is where the [GTA] would show examples. Show examples that's not always within the ranges. Show like a big variety of different examples that demonstrate different concepts.” (Dana, TA)

While instructors did not identify specific molecular spectra, they used online spectral databases or ChemDraw's spectra prediction feature to pull example spectra. Furthermore, instructors discussed only a handful of representations and analogies, often in tandem with other TSPCK components. For example, analogies were used to promote student understanding by increasing motivation through student relevance (e.g., comparing ¹H NMR spectroscopy to medical diagnostic tests) or leveraging student prior knowledge and curricular saliency to choose an analogy (i.e., comparing to other analytic methods). Instructors leveraged multiple analogies for introducing the purpose of NMR spectroscopy as an analytic method. They compared ¹H NMR spectroscopy to medical diagnostic tests such as magnetic resonance imaging, urinalysis, and blood analysis to relate to students’ prior experiences or interests.

“I think just showing like, this isn't just foreign to chemistry, but like something like that where you have everyone that's like pre-med and they'll be like, ‘oh that's actually kind of interesting now.’ So, mentioning that is always kind of neat.” (Steve, Novice)

Additionally, leveraging their students’ prior knowledge and curricular saliency, some instructors reported comparing analytical methods (i.e., thin-layer chromatography and IR spectroscopy) to ¹H NMR spectroscopy to “draw parallels” between the methods' capabilities. When discussing Q7 (Teaching procedures) for Group 4's Big Idea A: “How NMR Works/What Does it Do?” Kareem added “Use of analogies to draw parallel” commenting,

“So, I would probably say use of analogy to MRI and other testing methods like TLC. And then I might include like use of videos, drawings, simulations, those would be kind of tools that I might use.” (Kareem, Novice)

Analogies were infrequently used in addressing Big Ideas other than teaching students about molecular structure's role in ¹H NMR spectroscopy.

Instructors' emphasis on students’ understanding of molecular representations aligns with studies finding undergraduate students are still developing the ability to make connections between representations—such as molecular structure—and their underlying chemical properties and move in between two representations (Bodner and Domin, 2000; Kozma, 2003; Anderson and Bodner, 2008). Furthermore, instructors can use knowledge of how students develop spectral interpretation skills (e.g., Cartrette and Bodner, 2009 and Connor et al., 2021a,b) to inform the learning objectives they create at different course levels and align their teaching strategies with those objectives.

Furthermore, instructors only briefly discussed the importance of using appropriate example spectra for teaching about spectral features and interpretation but did not elaborate on how they go about choosing or using example spectra. Nor did they elaborate on how they utilize one or more representations at the same time. This finding may indicate the need to further understand how instructors teach with representations for this topic with observation data as well as make representational competence and skills explicit in chemistry curricula, instructional goals and teaching strategies (Popova and Jones, 2021; Gurung et al., 2022; Jones et al., 2022).

Conclusion and implications

The goal of this study was to capture post-secondary chemistry instructors' PCK for teaching ¹H NMR spectroscopy. To gain insight into this knowledge, participants were grouped based on experience and were tasked to construct a CoRe for teaching ¹H NMR spectroscopy in an introductory undergraduate course. Transcripts from the task as well as the completed CoRes were analyzed using Mavhunga and Rollnick's (2013) topic-specific PCK framework to capture instructors' knowledge for teaching this topic. The results from this study contribute to our understanding of the role that teaching context and experience play in instructor PCK and begin to reveal how ¹H NMR spectroscopy is taught.

The first component of topic-specific PCK, curricular saliency, reveals what topics are important to instructors for teaching ¹H NMR spectroscopy. Across all groups, instructors reported four spectral features as Big Ideas for learning ¹H NMR spectroscopy. In addition to these four features, science skills and practices made up the remainder of the Big Ideas, emphasizing the connection between content and disciplinary knowledge and skills. Furthermore, instructors’ role, context and disciplinary experience played a role in which concepts instructors chose and how instructors presented concepts.

Curricular saliency is under researched in PCK literature (Andrews et al., 2022). Thus, this study contributes to our understanding of instructors' curricular saliency and factors that influence the concepts they choose to teach. Pulling from findings from Couch et al. (2023), instructors commonly have limited opportunities for independent and collaborative curricular decision-making for their classrooms. However, findings from this study show that collaborative discussion and decision-making can act as knowledge-sharing and pedagogical growth opportunities (Couch et al., 2023) as demonstrated in how different groups identified different Big Ideas and each instructor's background informed chosen concepts. Thus, as a way to develop curricular saliency, we recommend that instructors not only reflect on what concepts they choose to teach in the course and why but also engage in conversations with colleagues within and outside of their department about their curricular decision-making.

During discussions around learners' prior knowledge and representations, instructors placed an emphasis on students having the ability to interpret concepts from, translate between, and use molecular representations, all of which are related to representational competence and skills (Kozma, 2003; Popova and Bretz, 2018b,c). Despite instructors' emphasis on students needing to develop representational competence and skills, instructors only proposed a handful of representational tools they use in class and did not describe how they are used or directed to students. Considering ¹H NMR spectroscopy is a representation-heavy topic including different types of representations (i.e., spectra, Lewis structures, spectroscopy tables), representational competence skills should be explicitly incorporated into the learning objectives and teaching practices of instructors.

Instructors reported three areas that make learning ¹H NMR spectroscopy difficult for students: (1) this topic includes abstract concepts, (2) chemistry vocabulary is a barrier, and (3) students have underlying assumptions that experimental data is absolute when interpreting spectra. The role these areas play in student understanding and problem solving have been extensively reported on in the literature (Bowen et al., 1999; Bhattacharyya and Bodner, 2005; Domin and Bodner, 2012; Pyburn et al., 2013; Haglund et al., 2015; Sevian et al., 2015; Popova and Bretz, 2018b; Quílez, 2019). Instructors reported that students' assumptions of absolute data lead to problematic use of heuristics and reasoning when interpreting spectra such as over-relying on the spectroscopy tables and using one-reason decision-making. We would like to echo Anderson et al. (2020) suggestion that textbooks—and we position instructors—take on systematic approaches to introducing and supporting student interpretation of spectral features to address these three areas of difficulty. Anderson et al. (2020) suggests scaffolding by introducing problems that focus on individual ¹H NMR features before introducing problems with multiple spectral features. This approach allows students to master analyzing individual spectral features before mastering problems with all four spectral features. By scaffolding problems in this way, students' cognitive load is reduced allowing students to understand how and why specific steps are taken in the problem-solving process. Thus, students can develop organized approaches to interpreting spectra, a characteristic needed to be a successful problem solver (Cartrette and Bodner, 2009).

Two emergent themes arose from instructors' knowledge of conceptual teaching strategies including (1) instructors' knowledge of conceptual teaching strategies primarily consisted of knowledge-telling strategies with few active strategies interspersed within the discussion and (2) instructors described responding to student affective experiences. For the first, extensive research in STEM instructional practices have demonstrated the extent of knowledge-telling strategies at the undergraduate level (Alexander et al., 1999; Raker and Holme, 2013; Stains et al., 2018; Zotos et al., 2021). This finding is partially due to PCK development (discussed further), as well as instructors carrying pedagogical norms of prior generations into their instruction.

For the second emergent theme for teaching strategies, instructors reported experiences with student affect aligned with previous research on organic chemistry students' affective experiences in the laboratory (Galloway et al., 2016; Connor et al., 2021a). Connor et al., (2019) observed their participants using gut feelings or negative affective states when interpreting spectral features. Galloway et al. (2016) found that students' affective experiences in the laboratory were shaped by their sense of autonomy in their learning which in turn affected their learning experiences. Thus, we encourage instructors to be mindful of their students' affective experiences when aligning instructional goals with pedagogical practice, as well as build and implement learning opportunities that create pedagogical partnership (Cook-Sather et al. 2021) and foster positive student outcomes.

Based on the findings from all components, we encourage instructors to reflect on their own learning objectives and instructional practices to identify what skills they want students to develop (e.g., representational competence skills, effective problem-solving skills). Instructors can then identify instructional strategies and practices that align with their learning and instructional objectives to effectively carry out instruction. Furthermore, results from this study show that teaching context, such as proximity to students and teaching experience, and disciplinary experience, play a role in reported PCK. For example, TAs were the only instructors to report posing questions to students in one-on-one interactions as opposed to experienced instructors who primarily reported picking and providing practice problems as active strategies. This is not inherently a problem as TAs and lead instructors have differing responsibilities that play a role in the strategies they propose and in extension implement. As such we encourage lead instructors to instead reflect on the opportunities they create for student learning and engage in PCK development through individual reflection or dialogue in communities of practice with colleagues. Additionally, for practitioners who work with TAs, we encourage lead instructors to reflect on how they train and prepare TAs for the classroom, as TAs often have more one-on-one interactions with students and play a role in student outcomes despite limited pedagogical training opportunities (Pentecost et al., 2012; Oleson and Hora, 2014; Zotos et al., 2021). Multiple pedagogical development interventions have been proposed in the literature for PCK development that lead instructors can implement in staff meetings such as self-reflection opportunities (Walkington et al., 2001), peer feedback (Ruder and Stanford, 2018), pedagogy groups (Capobianco et al., 2006), and using CoRes as a PCK development activity (Nilsson and Loughran, 2012; Mavhunga et al., 2016).

The findings of this study may be used as a reference for post-secondary organic chemistry instructors seeking to learn more about teaching ¹H NMR spectroscopy. The constructed CoRes and organized responses may be used for professional development opportunities or personal reflection leading to PCK development. Additionally, there are implications of future studies investigating how instructors create opportunities for students to develop problem-solving skills and representational competence skills in relation to spectral interpretation.

Author contributions

All authors contributed. M. C. and G. V. S. contributed to the conceptualization and revising of the study. M. C. and R. F. conducted data collection. R. F. and E. G. conducted data analysis for this study. The manuscript was written by R. F., with extensive, valuable feedback from G. V. S., E. G. and M. C. All authors read and approved the manuscript.

Conflicts of interest

There are no conflicts to declare.

Appendices

A1. Questions provided in the content representations

Big Ideas:

(1) What do you intend students to learn about this idea?

(2) Why is it important for students to know this?

(3) What else do you know about this idea (that you do not intend students to know yet)? *This includes more complex concepts that teachers choose not to present to students. Part of teaching is knowing how much detail or simplification to include so that students learn an accurate representation without confusion*

(4) Difficulties/limitations connected with teaching this idea. *Difficulties/limitations relates to student misconceptions and where models or go-to explanations fall short of explaining what's actually going on*

(5) Knowledge about students' thinking, which influences your teaching of this idea.

(6) Other factors that influence your teaching of this idea.

(7) Teaching procedures (and particular reasons for using these to engage with this idea).

(8) Specific ways of ascertaining students' understanding or confusion around this idea.

A2. Description of the codebook

We (the first two authors) developed the codebook (Table 6) from Mavhunga (2019)'s five components of topic-specific PCK. Each component was transformed into a code with definitions lifted from Mavhunga (2019).

Table 6 Codebook based on topic-specific PCK

Codes	Definition	Exceptions
Conceptual teaching strategies (STRAT)	These codes indicate when approaches for instructing material are addressed. This could either be very general (lab vs. lecture) or in very specific approaches for ^1H NMR instruction. This includes when graduate students talk about instructional strategies of the professor or lead instructor of the course. In addition, this can include teaching strategies the instructor deems inappropriate and/or knowledge of limitations of a strategy.
Curricular saliency (CURR)	These codes highlight interview data where the material to be taught, in past classes/current class/future learning, is brought forward. This could mean a variety of things, from teaching hands-on skills, to understanding the very basics of ^1H NMR spectral interpretation, to creating molecules from observed spectra. Curriculum refers to both the content that is presented in this foundational course on NMR and content presented in previous and future courses. This includes when the instructor knows of what students do not know and/or do not need to know. As well as when instructors talk about dimensions of assessment. Note: this doesn’t include knowledge of content.
Learners’ prior knowledge (LPK)	This code is used to show when instructors detail factors relating to the students' understanding of fundamental concepts related to ^1H NMR spectroscopy. This can but is not limited to when instructors discuss their views on their students’ knowledge and/or lack thereof (and how this might affect their learning) and developing conceptions students may have.	Do not code for LPK when talking about the lack of content knowledge in the context of students who would not have been taught that content before as this would be for curriculum.
What makes a topic easy or difficult (TED)	This code is used to capture when instructors discuss “knowledge of gate-keeping concepts within a topic that are difficult to understand and not necessarily misconceptions, and it triggers dedicated awareness and possible interventions for teaching them”. This code can also include what students may find especially difficult or easy to learn, and inherent traits that the topic may have that may affect how the instructor addresses material.	This code does not apply to developing conceptions.
Representations and analogies (RA)	This code is used to capture when instructors discuss using examples, illustrations, analogies, simulations, and models for teaching ^1H NMR Spectroscopy.

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A3. Summary of curricular saliency

All groups Big Ideas (Table 7) were consolidated together into one table to allow comparison across groups and Big Ideas. I (RF) condensed similar Big Ideas into one Big Idea to create a consensus of Big Ideas across groups. For example, Group 1's Big Idea “Understanding the concept and application/interpretation of chemical shifts”, Groups 2, 3, and 4's Big Idea of “Chemical Shift(s)”, and Group 5's Big Idea of “With respect to symmetry, unique hydrogens can be identified by independent signals/peaks/resonances” all captured the concept of identifying individual peaks within specific ranges of chemical shifts. These Big Ideas were thus condensed to “Chemical Shift”. I engaged in debriefing sessions with the experts in the research team (third and fourth author) to ensure trustworthiness of the condensed Big Ideas.

Table 7 All big ideas across groups

Group 1	Group 2	Group 3	Group 4	Group 5	Condensed big ideas
Defining spectroscopic methods generally as a way to bridge IR and NMR concepts from 211.	Chemical shifts	Equivalency/non-equivalency of Hs in a molecule	How NMR works/What Does it Do?	NMR fundamental theory – hydrogens in different environments interact with radio photons differently	Defining spectroscopy
Understanding the concept and application/interpretation of chemical shifts	Splitting	Chemical shift	Chemical shift	With respect to symmetry, unique hydrogens can be identified by independent signals/peaks/resonances	Understanding the instrument
Understanding the general concept of splitting patterns/what gives rise to splitting patterns	Integrations	Integration corresponding to number of equivalent Hs	Splitting/neighbors	Integrals aka (s) area (jk)	Equivalency
Understanding of integration and how it is affected by symmetry		Splitting of equivalent Hs	Molecular symmetry/3D visualization	Splitting/multiplicity	Chemical shift
Further application of NMR		How NMR instrument works	Fragments and degrees of unsaturation	Chemical shift	Multiplicity and splitting
Understanding NMR as a puzzle/protocol		NMR sample prep/lab skills	Proportionality and integration values	Integrated spectroscopy to identify unknowns	Integration
		Proposing/confirming molecule via spectrum		Using ^1H NMR to evaluate the progress of a chemical reaction	Laboratory skills
				Practical knowledge of preparing and obtaining NMR spectra (deuterated solvents, NMR tubes, spinning, locking, shimming)	^1H NMR spectral interpretation

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Acknowledgements

This work was supported by the Robert Kuczkowski Faculty Award and Rackham Graduate Student Research Grant. RF would like to thank the participants of this study for their time and knowledge in how they teach chemistry. A big thank you to everyone who provided feedback throughout the study and on the manuscript including Ina Zaimi, Daisy Haas, Solaire Finkenstaedt-Quinn, Amber Dood, Danielle Maxwell, and Dr. Daniel Steyer.

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