NMR Spectroscopy in the Undergraduate Curriculum - American

Chapter 4

“Spectroscopy First” for Interweaving and Scaffolded Learning in Organic Chemistry Downloaded by CORNELL UNIV on October 28, 2016 | http://pubs.acs.org Publication Date (Web): September 15, 2016 | doi: 10.1021/bk-2016-1221.ch004

Judith C. Amburgey-Peters* and Paul A. Bonvallet Department of Chemistry, The College of Wooster, 943 College Mall, Wooster, Ohio 44691, United States *E-mail: [email protected]

NMR spectroscopy typically appears in the middle of organic chemistry textbooks, leading to its introduction late in the first semester of a two-semester organic chemistry course. Such placement is understandable given the complexity of the topic and the intellectual skills necessary to solve spectroscopic problems. However, this approach misses the opportunity to integrate spectroscopic knowledge with early fundamental concepts and to present engaging new “puzzles.” As the next logical step in the evolution of our inquiry-based, learner-centered curriculum, we put IR and NMR spectroscopy at the beginning of our first-semester organic chemistry course. The course progression illustrates how theories (e.g., resonance, hybridization, and aromaticity) are developed based on evidence and demonstrates how organic chemists think and work. Our focus on the spectroscopic evidence behind key concepts and the way that knowledge is constructed creates a co-learning community promoting “mastery mentality.”

Introduction The higher-order thinking involved in understanding, interpreting, and judiciously using NMR data has an important position in undergraduate chemical education (1). This process parallels the scientific method in the sense that students collect information and develop a hypothesis that is consistent with available data. Despite the importance of spectroscopy, interpreting spectra may © 2016 American Chemical Society Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Downloaded by CORNELL UNIV on October 28, 2016 | http://pubs.acs.org Publication Date (Web): September 15, 2016 | doi: 10.1021/bk-2016-1221.ch004

be one of the most challenging skills in the undergraduate chemistry curriculum. Solving structural problems emphasizes method over memorization, as there is no low-level algorithm that guarantees success (2). NMR spectroscopy also has the potential to be isolated from the rest of the organic chemistry curriculum. It typically appears in the middle of most textbooks (3) and is so different from the previous and subsequent chapters that it can be challenging to find broader connections aside from the traditional use in identifying unknowns. While there are notable instances of NMR and/or IR being introduced before the second semester of a sophomore organic course (3–9), we describe here our commitment to a comprehensive multi-week integration of spectroscopy at the very beginning of our organic chemistry curriculum. Much like the “atoms first” approach in vogue with contemporary introductory chemistry, a “spectroscopy first” perspective focuses on scaffolded learning and a broad pedagogical narrative. We can build habits of mind in analyzing spectra and encouraging the interpretation of data (as opposed to memorization or blind faith) as the basis for understanding the structure and reactivity of organic molecules. We consequently have the opportunity to integrate NMR data at frequent points throughout the entire two-semester sequence as a means for better illustrating the experimental evidence behind key concepts.

Pedagogical Motivation Interweaving Knowledge of Structure A strong intuitive grasp of structure and bonding is an essential foundation for mastering organic chemistry. We build this understanding through three separate but closely interrelated areas in the overarching framework of our curriculum: describing structure, knowing structure, and transforming structure (Figure 1). By positioning the instrumental methods by which we determine structure at the beginning of organic chemistry, we can interweave this material (10) to introduce and reinforce other topics at the same time. IR and NMR spectroscopy, for example, are vehicles for building skills in drawing Lewis structures and recognizing functional groups—two topics that might have otherwise been taught in isolation during introductory chemistry or a period of review in the first weeks of organic chemistry. Each individual form of characterization (NMR, IR, and mass spectrometry) is introduced separately in our course and then integrated into composite problems to illustrate their complementary nature and relative strengths and weaknesses. Students learn about 1H NMR before 13C NMR, but the two methods are discussed in parallel. These composite problems are puzzles that require iterative problem-solving skills to develop a hypothesis based on clues, “puzzle pieces,” and the preponderance of evidence. This interwoven knowledge of structure and the instrumental methods of determining structure are helpful in developing a more sophisticated understanding of the composition of organic compounds, which in turn allows students to develop skills for predicting interactions and reactions of molecules based on structural and mechanistic thinking. 42

Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 1. Interconnected knowledge and skills from a structural perspective. Throughout the course we scaffold the processes of thinking, asking questions, using tools, and working “like an organic chemist.” Our students’ early fluency in NMR spectroscopy allows us to focus on structural evidence and higher-order procedural questions like “What data would you collect to determine the outcome of this reaction?” and “What are your predictions about what the data will look like?” throughout the year in the classroom and laboratory. As the course progresses, a strong foundation in structural and mechanistic thinking assists our students in the information management and problem-solving skills necessary to organize the complex matrix of organic reactions. Our synthetic laboratory activities involve practical questions such as cost, safety, and efficiency while integrating NMR spectroscopy to establish the identity and purity of our starting materials and products. Spectroscopy is our students’ primary tool for evidence of reaction outcomes, just as it is for most practicing organic chemists. Setting Classroom Culture We establish the expectation and classroom culture of “mastery mentality”: learning for the sake of improving, integrating, and applying knowledge (11, 12). We balance “mastery mentality” with the mindset of “performance mentality” which requires proving knowledge by working a problem or taking an exam. Using spectroscopy as the entry point into organic chemistry promotes mastery mentality. It allows students to interweave their prior knowledge by applying skills from introductory chemistry (such as drawing Lewis structures, understanding trends in electronegativity, and identifying hybridization) within a new context. This engagement reinforces the reality of science as a process of collecting and interpreting data rather than memorizing facts or reciting rules. Our first two weeks of organic chemistry used to be primarily a review of introductory chemistry. The deliberate review, while seemingly necessary, also had its problems. Our students could become complacent or bored with their studies because they encountered “the same old stuff” without any new stimulation or application. Some fell into the pitfall of viewing organic chemistry as an easy course that required little effort outside of class—an attitude that backfired later in the term when the material was new and more challenging. 43



Spectroscopy, by contrast, is a completely new topic for nearly all of our students. With IR and NMR spectroscopy at the beginning of the course, our students are immediately challenged to learn outside their comfort zone, and yet success is still realistically attainable with the right mindset and study habits. Spectroscopy provides an opportunity for us to “teach students how we think, not just what we know” (13). It captures the imagination by providing a tool for us to “see” structural information that is intrinsically un-seeable, thereby engaging a variety of learning styles and promoting higher-order thinking and problem solving. Many of our students show an intense curiosity and drive in solving the structural puzzle of an NMR spectrum, even with a complex set of data. Harnessing this inspiration and curiosity can help students to become more self-regulated learners (14). Connections to Course Philosophy It is easy to build an undergraduate chemistry curriculum that rewards only the consumption of knowledge. While basic information has indisputable value, researchers and professional chemists rarely review flash cards or solve problems that are accompanied by a solutions manual. As educators we seek to develop creators of knowledge—students who grow as scholars, scientists, and independent thinkers who succeed in the investigative process. The best researchers are not those who have memorized the most facts, but those who have a sufficient knowledge base and can effectively design and execute a practical plan for answering fundamental questions about the natural world. Our motivation for teaching spectroscopy first is based upon the precept that much of our knowledge in organic chemistry comes from spectroscopic data. Elucidation of reaction outcomes (15), organic structure, mechanism, dynamic processes, and kinetics (16) comes largely from spectroscopic experiments. NMR spectroscopy in particular provides rich structural information from basic one-dimensional data and even richer information with multi-dimensional data (17). As we help our students to learn about functional groups and apply spectroscopic tools, we balance “what we know” with “how we know it,” further enabling them to “think like an organic chemist.”

Implementation of Spectroscopy in the Curriculum Applying Spectroscopy to Other Topics The traditional classroom schedule, with the material defined in the manner and order prescribed by the textbook, potentially makes information a commodity to be presented and memorized. The absence of details about how the knowledge was gained or how its assumptions can be challenged does a disservice to students’ development as critical thinkers. While it would be impossible to present the experimental history of every aspect of organic chemistry in a single course, with spectroscopy as an initial focal point we have a valuable multi-faceted tool for probing scientific claims. We can teach new concepts and revisit prior knowledge 44 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


within the context of collecting and interpreting experimental data to justify those conclusions. Spectroscopy provides evidentiary support for a variety of fundamental concepts spread throughout our two-semester sequence (Table 1). Resonance theory, for example, is illustrated through spectroscopic investigation of N,N-dimethylformamide (DMF). Its carbonyl IR stretching frequency is lower than would be expected for an “ordinary” C=O bond, and NMR spectroscopy reveals that the methyl groups are non-equivalent at room temperature due to hindered rotation about the N—C partial double bond (18). The ability to “see” a molecule that is capable of resonance (19) provides another viewpoint from which to understand this sometimes-nebulous concept. During the organic courses, we present each topic in Table 1 roughly in the order listed. Whether the concepts are new and more advanced (e.g., aromaticity) or review and more basic (e.g., electronegativity), the fundamental concepts of organic chemistry can be introduced and re-visited through the lens of spectroscopic evidence—both in our course and lab, and again in subsequent advanced classes.

Table 1. Connections between Fundamental Organic Chemistry Concepts and Examples of the Spectroscopic Evidence That Support Them Concept

Spectroscopic Evidencea Conjugation lowers IR stretching frequencies because it imparts partial single bond character to a pi bond.

Resonance

The methyl groups of DMF are chemically inequivalent at room temperature.b Resonance effects contribute to keto-enol tautomerization equilibria.c

Electronegativity and bond polarity

Nuclei near electronegative elements tend to be deshielded and have increased chemical shift.

Hybridization

The greater the s character of the hybrid atomic orbitals making a bond, the higher the vibrational frequency and (often) the higher the chemical shift of the connected atoms.

Conformational analysis

Splitting pattern analysis provides evidence that substituents preferentially occupy the equatorial position on a cyclohexane backbone.b

Stereochemistry

Enantiotopic vs. diastereotopic protons give characteristically different signals and splitting patternsd and can be used to determine the stereochemistry of products in the Wittig reaction.e In IR, the O—H stretch in 1-butanol is sharper and has a higher frequency in the gas phase vs. the liquid phase.

Hydrogen bonding Hydrogen-bonded protons tend to have higher chemical shift and broader signals than those that are not. Continued on next page.

45 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Table 1. (Continued). Connections between Fundamental Organic Chemistry Concepts and Examples of the Spectroscopic Evidence That Support Them Spectroscopic Evidencea

Concept

Signals for N—H and O—H are broad and can disappear with a “D2O shake.” b


Acid-base reactions

The acidity of a proton generally correlates with its chemical shift (e.g., phenolic vs. aliphatic alcohols, carboxylic acid vs. alcohol hydroxyl).

Nucleophilicity and electrophilicity

Deshielded atoms tend to have higher chemical shift and often are electrophiles.b

Aromaticity

The diamagnetic ring current has a deshielding effect on the nuclei of benzene and other aromatic compounds.b

a NMR spectroscopy, unless specified otherwise.

Reference (19).

d

Reference (15).

e

b See reference (18) for greater detail. References (20, 21).

c

Hybridization: A Case Study Hybridized atomic orbitals provide another context for integrating spectroscopy with fundamental concepts. Given the importance of bond angles and atomic geometry to the structure and reactivity of molecules, the concept of hybridization often appears first in introductory chemistry and is further emphasized in organic chemistry. By examining spectroscopic data, we help students understand hybridization in new ways beyond the algorithmic counting of bonding and nonbonding electron pairs around an atom. The increasing IR vibrational frequency of the carbon-carbon bond in the progression from alkanes to alkenes to alkynes (Figure 2) is rationalized by Hooke’s law as the increasing vibrational force constant of single vs. double vs. triple bonds (22). The data supports the general trend that stronger bonds vibrate at higher frequencies than weaker bonds. As a corollary, the carbon-hydrogen bonds within each of these hydrocarbon functional groups must also have subtly but systematically different strengths (vibrational force constants), since we observe an increase in C—H stretching frequency from alkanes to alkenes to terminal alkynes (Figure 2). Thus, the greater the s character of a hybridized atomic orbital, the shorter and stronger the bond that it participates in, and consequently the higher the vibrational frequency of the bond. The overarching message is that a logical and predictable connection exists between IR spectroscopy and hybridization. The patterns in NMR spectroscopy are more nuanced. We have students examine a data set (Figure 3) and then develop a logically consistent explanation for the trends. They can “discover” the loose correlation between hybridization and chemical shift. Noting that hybrid atomic orbitals with greater s character (sp and sp2) are “more electronegative” than those with less s character (sp3) (22) allows them to successfully predict the relative 1H and 13C NMR chemical shifts of unsaturated versus saturated hydrocarbons. However, the chemical shift trend 46



for carbon and hydrogen atoms is inconsistent when comparing acetylenic systems (involving sp hybrid atomic orbitals) to vinylic systems (involving sp2 hybrid atomic orbitals.) Hybridization differences do not explain why an acetylenic hydrogen has a lower chemical shift than a vinylic hydrogen. The data forces the students to seek an alternative logically consistent explanation. We have the students note the chemical shift trends of the acetylenic and vinylic hydrogens, along with the aromatic hydrogens. Then, we have them consider the pi cloud orientations. The apparent “contradictions” permit the cursory introduction of anisotropic effects caused by ring currents in the neighboring pi bonds. Later, we return to anisotropy in greater depth within the context of alkynes, acetylenic hydrogen reactivity, and aromaticity. The approach also illustrates the important difference between memorizing a trend or generalized rule versus understanding the physical phenomena that contribute to spectroscopic observations on which the generalizations are based.

Figure 2. IR stretching frequencies of carbon-carbon and carbon-hydrogen bonds, see (22).

Figure 3. Comparison of chemical shift data from reference (23) for a representative alkane, alkene, and alkyne. 47 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Promoting Higher-Level Thinking With a conceptual and evidence-based foundation in place, students can be challenged with higher-order open-ended assignments using the textbook problems as a starting point. For example, an exercise like “Draw the major resonance structures of molecule X” can be followed by “Annotate the IR and NMR spectra of molecule X to show evidence of resonance delocalization.” Countless other examples are possible, ranging from evidence obtained from NMR chemical shift and coupling constants to the frequency and intensity of IR signals. Such integrative activities provide an opportunity for students to show not just factual recall, but a deeper integrative and intuitive understanding of chemistry (Figure 4). These multi-tiered questions can appear in collaborative problem-solving sessions in class and the “stretch” question on exams. The guiding principle is that students are challenged to find and explain how spectroscopic data is consistent or inconsistent with a given hypothesis, rather than answering a question by reciting a rule.

Figure 4. Sample integrative questions from exams and group activities that combine basic concepts with structural reasoning based on NMR. Oftentimes, in the classroom and laboratory alike, spectroscopic data can directly contradict a prediction. Scientists tend not to view such situations as “wrong” but as opportunities to examine assumptions and thereby advance our knowledge and refine their hypothesis (15). The case study of NMR chemical shift trends in relation to hybridization (Figure 3) is one example. As another, we evaluate the two possible products of HBr addition to 2-methylbut-2-ene. One might predict compound A as the major product because the secondary alkene 48 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


carbon atom in the reactant is less sterically hindered than the tertiary carbon (Figure 5). Such a prediction is perfectly reasonable in the absence of any data. The 1H and 13C NMR spectra of the major product, however, are inconsistent with compound A and consistent with compound B.

Figure 5. Top: Potential products from the addition of HBr to 2-methylbut-2-ene. Bottom: Simulated 1H NMR spectrum of the major product, from reference (24). The spectral evidence invites fundamental questions: What is the mechanism of the reaction? What are the thermodynamic and kinetic factors that govern the selectivity? Can the reaction conditions be changed to reverse the selectivity in favor of compound A? The question of which product predominates can be answered quickly by reciting the Markovnikov rule, but such an approach misses the opportunity to show the cycle of inquiry and evaluation that scientists actually undertake. Rules may describe a phenomenon, but they do not explain why it occurs. The practice of prediction and examination of data can be used in many contexts, including the Zaitsev/Hofmann product distribution in the E2 reaction, substituent activation and directing effects in electrophilic aromatic substitution, and the endo rule in the Diels-Alder reaction.

Opportunities and Challenges with “Spectroscopy First” Bringing Spectroscopy Theory to Practice One of the greatest advantages of “spectroscopy first” is the emphasis on evidence, which provides immediate and meaningful applications in the laboratory. Our entire first-semester laboratory course is constructed as a multi-week synthetic experiment (Figure 6) in which students adapt a procedure from the literature (25). Even though the mechanistic details of the reaction do not emerge until later in the course, in our first laboratory meeting we communicate 49 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


the importance of confirming the identity and purity of the starting materials prior to a chemical synthesis. We set the goal of each student obtaining experimental and standard IR and NMR spectra of the catechol and 2-chloroethanol reactants by the third laboratory session. By this point, the students have established a baseline level of skill in spectroscopic interpretation which they share in a “research group meeting” the next week to present and interpret their data in collaboration with peers. We have an early opportunity to establish the key habits of documenting data, assigning each signal to a specific structural feature, annotating spectra to show evidence of understanding, and confirming the suitability of the reagents. As the students’ knowledge of reactivity grows, we interweave content as we re-visit the reaction at various times in the classroom to identify nucleophiles and electrophiles, evaluate possible mechanisms, rationalize the observed product(s), and recognize the reaction as a Williamson ether synthesis. We measure the transference of knowledge between lab and class by including the reaction as an exam question, either indicating 1 mole or excess of 2-chloroethanol. Many students demonstrate a solid understanding, but this allows us to identify how many of the students, and who, need additional attention.

Figure 6. Synthetic scheme for our first-semester organic laboratory project. In terms of higher-order thinking, the presence of impurities (e.g., water or residual solvent) or unpredicted and undesired products (e.g., the monosubstituted compound 1) in the samples adds to the intellectual complexity of interpreting “real” spectra as opposed to “textbook” spectra. By the time we begin the reaction in the fifth laboratory session, our more insightful students offer evaluative statements about the relative utility of each type of spectroscopy. For instance, some point out that IR is less useful than NMR in this project because every reactant and potential product contains a hydroxyl functional group. Just as in the classroom, we promote the practice of predicting spectra of the product and then evaluating how well a data set matches that expectation. The class usually obtains a variety of results, ranging from pure target ether 2 to pure mono-substituted intermediate 1 to a mixture of both materials. When mixtures of 1 and 2 are obtained, we also have the opportunity to apply NMR quantitatively to determine the ratios of the materials (21). The subsequent “group meeting” presentation and lab report discuss each type of experimental data as the students make a claim about the success of their reaction supported by evidence. Despite their similar 1H NMR spectra, compounds 1 and 2 can be readily differentiated by the symmetry of the signals in the aromatic region and the integration of the aliphatic protons. Such an analysis builds the skills in critical thinking necessary for our Independent Study research program at the College of Wooster (26) while also modeling the physical and mental process of what organic 50



chemists do in their research. We reinforce the understanding that there is not just one way to approach a question, and that real problem solving is an iterative, rather than linear, process. One advantage to the group meeting approach is that all students have the opportunity to analyze their own data, which may be the simple situation of pure desired product, along with seeing the range of other possibilities. Again, the transference of knowledge and skill can be probed by an exam question that includes interpretation of real spectral data for one of the more complicated outcomes. The early integration of spectroscopy illustrates the connections between class and lab (research) while promoting intellectual curiosity. Establishing a co-learning, co-creating, co-questioning community among our students has both broadened and deepened our organic chemistry community. As compared to “delivery of information” in the same order as our textbook, the atmosphere is more collaborative, more engaging, and more fun for instructors and students alike. The faculty and student mindset is growth-oriented (27) rather than evaluative or focused on correct vs. incorrect answers. Teachers and learners who are having more fun are better able to integrate humor and community, which in turn enhances the learning (28). Promoting Good Study Habits Another advantage to starting our classroom and laboratory curricula with spectroscopy is that it is an “academic equalizer.” With very few exceptions, our students have no previous experience with IR and NMR spectroscopy. The immediate challenge of new skills and concepts helps to set the clear expectation that all students need to follow our suggestions for study skills and habits in organic chemistry. The stronger students quickly realize that they do indeed need to practice outside of class, while the interweaving of prior knowledge (e.g., Lewis structures and hybridization) within the new context of spectroscopy helps our students with weaker backgrounds to strengthen their foundation. Spectroscopy establishes the importance of continuous work and learning outside of the classroom with the expectation of active engagement in the classroom. We also have daily online homework assignments due for each class that focus on practicing fundamental skills and knowledge retrieval (10). The integration of class and lab (theory and practice) also provides some of the “wow factor” of how the information in the textbook was assimilated and where theories and hypotheses come into play. Two weeks of reviewing formal charge and resonance do not inspire curiosity nearly as well. Getting to use data from modern instruments (whether in-house or online) and learning more about the instrumentation and methods engages the students in what organic chemists do. Connections to Future Learning Spectroscopy is used broadly in many different scientific contexts. Thus, our broader purpose is to equip our diverse population of students with transferrable skills and the understanding of physical phenomena from different viewpoints. For example, students of inorganic chemistry see the consequences 51



of investigating paramagnetic samples by NMR, while those in physical chemistry could investigate the temperature dependence of bond rotation in DMF. Some advanced courses incorporate the analysis of two-dimensional and non-first-order NMR spectra. Students also encounter spectroscopy outside of the chemistry curriculum—such as UV-visible absorption in a biochemical assay or photoelectron spectroscopy in physics—or in the context of an undergraduate research project, so the transference of evidence-based “spectroscopic thinking” into other intellectual domains is beneficial. We believe that this type of learning is best accomplished when skills in data interpretation are integrated into mastering the factual content of the course material. Potential Drawbacks One challenge of putting spectroscopy first is that most organic chemistry textbooks introduce spectroscopy in the middle chapters (3). The faculty must therefore be more deliberate about directing students to the appropriate readings and homework problems. We use weekly Roadmaps (analogous to lesson plans and schedules in formalized educational training) that we share with the students (Tables 2 and 3). The Roadmaps clearly outline the reading, guiding questions (29), in-chapter and end-of-chapter textbook problems, and online homework that our students are expected to complete or at least attempt prior to coming to each class. The initial faculty labor involved in providing such a high level of detail and planning in the Roadmaps has paid dividends in other ways. We have adopted the philosophy of a “flipped” classroom—moving the transmission of information outside of the classroom and using class time for higher-order tasks—without filming video lectures or creating much additional work for ourselves. We have established an active learning environment where the students are expected to do as much work before class as the instructor (30, 31). Our schedule framework is shared with and implemented by visiting faculty who can integrate into our holistic organic curriculum while focusing more on what they are doing with their students in the classroom and lab rather than trying to design a curriculum and schedule. The teachers and students both share a responsibility for learning and creating questions that lead to more learning. We are all teachers and students. Putting spectroscopy first and jumping around the textbook also establishes the expectation that learning can be a bit of a “scavenger hunt” rather than reading a book from beginning to end. Our directed approach for seeking specific information allows the interweaving of knowledge (10) and develops some fundamental information literacy skills such as using the Roadmap, textbook index, and online sources to find the targeted information. In the lab, the students are expected to find standard spectroscopic data to compare to their predictions and collect experimental data for their starting materials and reaction products. We model for students the process of asking questions and seeking answers as we help them begin to pose their own questions as developing researchers and professionals. The greatest challenge with our “spectroscopy first” curriculum is with transfer students, especially those who have taken only one semester of organic 52 Soulsby et al.; NMR Spectroscopy in the Undergraduate Curriculum: First Year and Organic Chemistry Courses Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


chemistry and are seeking to enroll directly into our second-semester course and lab. We interview each transfer student to learn about their previous experience with spectroscopy. For students who have had no or limited exposure to IR and NMR, we recommend that they repeat the first semester of organic chemistry at our institution because of the spectroscopy-heavy components of the classroom and laboratory. Students who begin our sequence at the start of the year versus mid-year demonstrate clear differences in mindset, problem-solving skills, and consequently grades. We have also faced the logistical challenge of needing more experimental NMR data. Without an automated sample changer, we have developed a team of organic lab assistants who collect the data and process it offline, then provide electronic data to the students. The next logical step in our growth is to train interested students to use the offline software themselves.

Table 2. Condensed Roadmap for IR Spectroscopy Readinga,b Class Day 1

Topics and Guiding Questions Course management: What are your goals? Lewis structures and line-angle formulas: How do organic chemists describe structure?

Class Day 2 Targeted reading assignments from various chapters

In-Class Problem Solving Sessionc What are some common ways that chemists use to depict the structure of molecules? What patterns do you recognize in the assignment of formal charge? How can you evaluate which resonance structures are major, minor, or insignificant contributors to the resonance hybrid? What are the benefits of drawing electron-pushing arrows?


Polarity of bonds and molecules How can the polarity of a covalent bond be predicted? Why is the distribution of electrons important? Describing structural patterns What is the benefit of the “functional group” organizational system? How do chemists know which functional groups are present?

Class Day 4 Targeted reading assignment (IR chapter)

Infrared spectroscopy What happens when an organic molecule absorbs infrared light? What determines the frequency and intensity of a bond vibration? Why are some vibrations IR-inactive?


In-Class Problem Solving Sessionc How can IR spectroscopy be used to identify functional groups? As you learn the IR signature of each functional group, how can you balance memorizing vs. using data tables?


Uses of IR spectroscopy Identifying an unknown – what can IR tell you about a molecule? What are its limitations? Validation of resonance – what evidence is there? What are the correlations between hybridization and IR frequency? How does IR spectroscopy provide evidence for hydrogen bonding? Continued on next page.


Table 2. (Continued). Condensed Roadmap for IR Spectroscopy Readinga,b

Topics and Guiding Questions

Class Day 7 Targeted reading assignment (IR/MS chapter)

What type of information does a mass spectrum provide? How can you determine the empirical formula of an unknown compound? The molecular formula? How can MS and IR be used together?

Class Day 8

Exam 1d


a

To be completed before each class. We highlight the highest-priority sections in bold. b Accompanied each day by online and textbook practice problems, which are solved beforehand in a dedicated problem-solving notebook and brought to class. c Worksheets to promote peer interaction. d Exams come early and frequently to lower the stakes and promote mastery (29).

Table 3. Condensed Roadmap for NMR Spectroscopy Readinga,b


Class Day 9 Targeted reading assignment (NMR chapter)

Interpreting 1H NMR spectra How is NMR connected to the “big picture” from the previous three weeks of the course? What happens to a molecule inside an NMR spectrometer? What does the number of signals in an NMR spectrum tell you about the structure of a molecule? What does a signal’s chemical shift tell you about structure? What does a signal’s integration tell you about structure? What does a signal’s splitting pattern tell you about structure?

Class Day 10 Targeted reading assignment (NMR chapter)

Differentiation of isomers How do 1H and 13C NMR spectroscopy compare / contrast? How can 1H and/or 13C NMR be used to differentiate structural isomers? Cis-trans isomers? What is a coupling constant, and what information about structure does it provide? When does complex splitting occur?

Class Day 11 Solve assigned spectral problems

In-Class Problem Solving Sessionc Integration: Solving composite problems How can you combine IR and NMR data to determine the structure of an unknown compound?


Further integration: Structures from data Mastering Composite Problem Solving How can you know the empirical formula of an unknown compound? Its molecular formula? How are elements of unsaturation related to molecular structure? What are some strategies for combining IR, NMR, and MS data to find the structure of an unknown compound? Continued on next page.


Table 3. (Continued). Condensed Roadmap for NMR Spectroscopy Readinga,b



NMR evidence to support key concepts How does the 1H NMR of DMF support the theory of resonance? How do polarity and anion stability relate to acid-base strength? How is this reflected in 1H NMR spectroscopy? How does a “D2O shake” experiment demonstrate that alcohols and amines possess exchangeable hydrogens? Can you write a chemical equation showing the reaction?

Class Day 14

Exam 2d


a

To be completed before each class. We highlight the highest-priority sections in bold. b Accompanied each day by online and textbook practice problems, which are solved beforehand in a dedicated problem-solving notebook and brought to class. c Worksheets to promote peer interaction. d Exams come early and frequently to lower the stakes and promote mastery (29).

Focusing on Longitudinal Development Early exposure to spectroscopy promotes our broad long-term goal of empowering students to learn by asking questions and using data. The most noticeable trends have been in the laboratory, where students follow the high-impact educational practice of applying knowledge from the classroom (32). As one sign of engagement, our students frequently want extra time in the lab and more NMR tubes to collect additional spectra for their synthetic project—not because they have to, but because they want to. IR and NMR data provide formative feedback on the scientific process, revealing the consequences of past actions and informing the future steps in an experiment. The evolution of our organic program is a process-oriented approach similar to “action research” that “involves intervention in an operating classroom setting” (33). Our decision to use spectroscopy for a specific purpose—for understanding fundamental concepts in the classroom and making evidence-based decisions in the laboratory—is one such intervention. We take the idea of action research one step further by intimately integrating the classroom and laboratory to encourage evidence-based decision making and sensible scientific conclusions, bringing theory to practice. Some signs of success come from a combination of specific short-term observations and broader longitudinal outcomes. In the laboratory, our students spend 14 weeks in the first semester preparing for, carrying out, and reporting on their synthetic project. They progress from using spectroscopy in simple ways (confirming the identity and purity of reactants) to more complex ways (analyzing a mixture, evaluating the overall success of the project) that culminates in a comprehensive written report and oral presentation to the class. The formal presentation is an exercise in mastery mentality that gives an opportunity to tell a “story” about the project as embodied by the iterative cycle of asking questions, collecting data, and taking appropriate action in response. These skills are further developed in the second semester of the laboratory, where students 55



repeat the first-semester reaction in only four weeks (guided by the future work that they proposed in the first semester) and report once more on their results. They show clear improvements in experimental efficiency, accuracy and depth of understanding in data interpretation, supporting claims with evidence, scientific professionalism, and overall intellectual ownership of their work. Looking longitudinally, we note that the students in our advanced organic chemistry class are well prepared to compare predicted NMR data with experimental data and critically evaluate the strengths and limitations of such information. Students from majors outside of chemistry have asked for training on the NMR spectrometer so that they can use structural evidence in their research. Our Senior Independent Study students have a better overall understanding of the research process and the value of critically examining spectroscopic evidence to inform decisions and draw conclusions. These higher-order skills evolve gradually and holistically, so we are working to develop a more formalized assessment of the short term and longitudinal impacts and outcomes.

Conclusions NMR spectroscopy has the obvious application of characterizing unknown organic compounds, but it serves many more purposes. Bringing spectroscopy to the beginning of the organic chemistry curriculum leads to advantages in pedagogy, classroom environment, and development of “mastery mentality” for students and faculty alike. Our scaffolded, evidence-based approach establishes an intellectual community where scientific knowledge is connected with experimental data, problem solving, iterative learning, and curiosity.

Acknowledgments We are grateful to the National Science Foundation (grant CHE-9977546) for its support of a 400 MHz NMR spectrometer at the College of Wooster. We are also indebted to the generations of Wooster students who have helped us design and revise this curriculum. We thank the many faculty who have worked with us in various capacities, in particular Nicholas N. Shaw, Crystal Young-Erdos, and Sibrina N. Collins.

References 1.

2. 3.

NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013. Cartrette, D. P.; Bodner, G. M. Non-Mathematical Problem Solving in Organic Chemistry. J. Res. Sci. Teach. 2009, 47, 643–660. Livengood, K.; Lewallen, D. W.; Leatherman, J.; Maxwell, J. L. The Use and Evaluation of Scaffolding, Student Centered-Learning, Behaviorism, and Constructivism to Teach Nuclear Magnetic Resonance and IR Spectroscopy 56


4. 5.

6.


7. 8.

9.

10. 11. 12.

13. 14.

15.

16.

in a Two-Semester Organic Chemistry Course. J. Chem. Educ. 2012, 89, 1001–1006. Solomons, T. W. G.; Fryhle, C. B.; Snyder, S. A. Organic Chemistry, 11th ed.; Wiley: New York, 2014. Christiansen, M. A.; Crawford, C. L.; Mangum, C. D. Less Cookbook and More Research! Synthetic Efforts Toward JBIR-94 and JBIR-125: A Student-Designed Research Project in a Sophomore Organic Chemistry Lab. Chem. Educator 2014, 19, 28–33. Reeves, P. C.; Chaney, C. P. A Strategy for Incorporating 13C NMR into the Organic Chemistry Lecture and Laboratory Courses. J. Chem. Educ. 1998, 75, 1006–1007. Gravert, D. J. Two-Cycle Organic Chemistry and the Student-Designed Research Lab. J. Chem. Educ. 2006, 83, 898–901. Corbin, P. S. From a Non-Majors Course to Undergraduate Research: Integration of NMR Spectroscopy across the Chemistry Curriculum at Ashland University. Abstracts of Papers, 247th ACS National Meeting & Exposition, Dallas, TX, March 16−20, 2014; American Chemical Society: Washington, DC, 2014; CHED 72. Hanson, R. M.; Lancashire, R. J.; Patiny, L. Real-time Classroom Comparison of Structures and NMR Spectra Using Jmol/JSpecView and Nmrdb. Abstracts of Papers, 249th ACS National Meeting & Exposition, Denver, CO, March 22−6, 2015; American Chemical Society: Washington, DC, 2015; CHED 39. Brown, P. C.; Roediger, H. L.; McDaniel, M. A. Make It Stick: The Science of Successful Learning; Belknap Press: Cambridge, MA, 2014. Kulik, C.-L. C.; Kulik, J. A.; Bangert-Drowns, R. L. Effectiveness of Mastery Learning Programs: A Meta-Analysis. Rev. Educ. Res. 1990, 60, 265–299. Bonvallet, P. A.; Amburgey-Peters, J. C. Using Course-Embedded Research in the Organic Chemistry Laboratory to Promote Mastery Mentality and “Thinking Like a Chemist.” Abstracts of Papers, 247th ACS National Meeting & Exposition, Dallas, TX, March 16−20, 2014; American Chemical Society: Washington, DC, 2014; CHED 118. Talanquer, V.; Pollard, J. Let’s Teach How We Think Instead of What We Know. Chem. Educ. Res. Pract. 2010, 11, 74–83. Nilson, L. B. Creating Self-Regulated Learners: Strategies to Strengthen Students’ Self-Awareness and Learning Skills; Stylus Publishing: Sterling, VA, 2013. Wachter, N. M. Using NMR To Investigate Products of Aldol Reactions: Identifying Aldol Addition versus Condensation Products or Conjugate Addition Products from Crossed Aldol Reactions of Aromatic Aldehydes and Ketones. In NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 91–102. Kantorowski, E. J.; Ghaffari, B. D.; Macrorie, A.; Candee, K. N.; Petraitis, J. M.; Miller, M. M.; Warneke, G.; Takacs, M.; Hancock, V.; Lusth, Z. A. NMR-Based Kinetic Experiments for Undergraduate Chemistry Laboratories. In NMR Spectroscopy in the Undergraduate Curriculum; 57


17.

18.


19.

20.

21.

22.

23.

24. 25.

26. 27. 28. 29.

30.

Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 211–228. Miller, V. R. Use of HSQC, HMBC, and COSY in Sophomore Organic Chemistry Lab. In NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 103–128. Bonvallet, P. A.; Amburgey-Peters, J. C. Data versus Dogma: Introducing NMR Early in Organic Chemistry to Reinforce Key Concepts. In NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 45–55. Marsh, A. L. Using NMR Spectroscopy to Elucidate the Effect of Substituents on Keto-Enol Equilibria. In NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 205–210. Hanson, J.; Dasher, B.; Scharrer, E.; Hoyt, T. Exploring the Stereochemistry of the Wittig Reaction: The Unexpected Influence of a Nominal Spectator Ion. J. Chem. Educ. 2010, 87, 971–974. Cramer, J. A. Using NMR Spectroscopy to Promote Active Learning in Undergraduate Organic Laboratory Courses. In NMR Spectroscopy in the Undergraduate Curriculum; Soulsby, D., Anna, L. J., Wallner, A. S., Eds.; ACS Symposium Series 1128; American Chemical Society: Washington, DC, 2013; pp 57–68. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvyan, J. A. In Introduction to Spectroscopy, 4th ed.; Brooks/Cole: Belmont, CA, 2009; pp 20, 36–37, 126–127. AIST:Spectral Database for Organic Compounds, SDBS. http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi (accessed November 19, 2015). ChemBioDraw Ultra, version 14; CambridgeSoft, 2014. Bogaschenko, T.; Basok, S.; Kulygina, C.; Lyapunov, A.; Lukyanenko, N. A Practical Synthesis of Benzocrown Ethers Under Phase-Transfer Catalysis Conditions. Synthesis 2002, 2266–2270. Independent Study, The College of Wooster. https://www.wooster.edu/ academics/research/is/ (accessed August 24, 2015). Dweck, C. S. Mindset: The New Psychology of Success; Ballantine Books: New York, 2008. Stambor, Z. How Laughing Leads to Learning. APA Monitor on Psychology 2006, 37, 62–65. Saville, B. K.; Lambert, T.; Robertson, S. Interteaching: Bringing Behavioral Education into the 21st Century. The Psychological Record 2011, 61, 153–166. Weimer, M. Learner-Centered Teaching: Five Key Changes to Practice, 2nd ed.; Jossey-Bass: San Francisco, 2013.



31. Weimer, M. Five Characteristics of Learner-Centered Teaching http://www.facultyfocus.com/articles/effective-teaching-strategies/fivecharacteristics-of-learner-centered-teaching/ (accessed August 31, 2015). 32. Kuh, G. D.; Schneider, C. G. High-Impact Educational Practices: What They Are, Who Has Access to Them, and Why They Matter; Association of American Colleges and Universities: Washington, DC, 2008. 33. Hunter, W. J. F. Action Research as a Framework for Science Education Research. In Theoretical Frameworks for Research in Chemistry/Science Education; Bodner, G. M., Orgill, M., Eds.; Pearson Prentice Hall: Upper Saddle River, NJ, 2007; pp 152–171.


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