Article pubs.acs.org/jchemeduc
Using a Problem Solving-Cooperative Learning Approach To Improve Students’ Skills for Interpreting 1H NMR Spectra of Unknown Compounds in an Organic Spectroscopy Course Rihab F. Angawi* Department of Chemistry, College of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia ABSTRACT: To address third- and fourth-year chemistry students’ difficulties with the challenge of interpreting 1H NMR spectra, a problem solving-cooperative learning technique was incorporated in a Spectra of Organic Compounds course. Using this approach helped students deepen their understanding of the basics of 1H NMR spectroscopy and develop abilities to think skillfully and apply these skills to elucidate structures from spectra more consistently. The multistep method allowed for increased instructor feedback, as each step was evaluated by grading students’ work. Assessment of the overall method was performed using two evaluation tools. A comparison of students’ cumulative grades for three consecutive years with and without using the approach was made, and the resulting statistical data demonstrate an improvement in student performance for the treatment groups relative to the control group. The second tool was the survey data. Analyzing students’ feedback in the last step of the method closely mirrors how students’ acceptance of the proposed approach was meaningful, which was also supported by the positive comments of students. All student work is used with permission. KEYWORDS: Upper-Division Undergraduate, Organic Chemistry, NMR Spectroscopy, Problem Solving/Decision Making, Collaborative/Cooperative Learning, Second-Year Undergraduate
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steps on how to use 1H NMR data to deduce the chemical structure. Starting in 2002 and up until 2009, a traditional method was used to explain to the students how to interpret a 1H NMR spectrum of an unknown organic compound and elucidate its structure. This was done by analyzing each signal in the spectrum by pointing out its chemical shift and multiplicity/ coupling constant. In some cases, supplementary data from IR or 13C NMR were given to facilitate the interpretation. This strategy worked well with small compounds and was achieved with minimal errors. However, for larger structures, the method was ineffective. The difficulties usually arise from the greater number of signals with more complicated multiplicity patterns that led the students to misinterpret the whole spectrum. Some students overlooked portions of the spectrum and, therefore, lost some of the structural characteristics of the unknown compound. Other students miscalculated the number of signals or misread the multiplicity, particularly the overlapped ones. Others misapprehended the fundamental elements of a spectrum such as correlating the number of signals to the number of protons in the molecule, the existence of exchangeable proton(s) with respect to the molecular formula given and the presence of functional groups in accordance with the value of the chemical shift of some signals. Other students solved the multiplicity of each signal individually and correlated it to the number of neighboring protons but failed to put together pieces of the molecule consistently with regards to its data. As a natural
INTRODUCTION Teaching NMR spectroscopy to undergraduate students is a complex task because it involves implementing conceptual understanding and problem solving skills into one course. In addition, solving a spectrum of unknown chemical structure has the potential to be particularly challenging because there is no straightforward protocol or single generalized strategy to follow. Nevertheless, a wealth of spectroscopic data can be deduced from a single 1H NMR spectrum that, if used logically, can lead to positive outcomes.1 Most spectroscopy and organic chemistry text books illustrate a few general rules to interpret 1 H NMR spectra; however, these resources are not sufficient for students’ learning.2−7 As a natural outcome, students often develop a negative attitude toward the subject and instructors find it difficult to include spectral interpretation questions in exams. Several studies have been devoted to overcome this difficulty.8−12 At King Abdulaziz University (KAU), the Spectra of Organic Compounds course (Chem 333) is taught to third- and fourthyear students. It presents challenges for students as well as instructors because too often, students come to this class with the idea that spectral data, primarily NMR, are difficult to interpret and spectra are almost impossible to solve. This sense of difficulty was recorded among almost all the students when attempting to solve a 1H NMR spectrum of an unknown organic compound. An important and crucial cause of this high anxiety and negative attitude could have been the way these data are misinterpreted, mistakenly ignored, or wrongly mastered. This can be attributed to the lack of guidelines or © XXXX American Chemical Society and Division of Chemical Education, Inc.
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understanding of the shielding and deshielding phenomena of protons and pinpoint the reasons, students were asked to assign the highest upfield and downfield signals in the spectrum and associate them with the strongest shielded and deshielded protons on the structure. Most of the students answered this part of the quiz correctly, but a few were confused. Nevertheless, performing this progressively, the students were, ultimately, able to recognize the misapprehension that was associated with the concept of chemical shift and could, unambiguously, identify each signal and correlate it to its proton type. This promoted confidence in their ability and encouraged the professor to go one step further. In an effort to establish a cooperative learning atmosphere, the students were divided into pairs. Group members started to communicate and many mistakes were discussed and corrected. Eventually, an open class discussion with the professor was initiated to ensure that complete comprehension and deeper understanding of the contents had been developed. Moving through the semester, another type of spectral problem with a higher level of complexity was used. The problem was chosen to further emphasize the effect of functional groups and heteroatoms on the shielding and deshielding of the nearby protons and to introduce the students to the concept of signal multiplicity. A 1H NMR spectrum with two alternative structures was provided to each group and they were asked to work collaboratively during a 25 min period and assign the structure that belongs to the spectrum. To do this, the students were instructed to analyze each structure in terms of the number of different sets of protons and the anticipated number of signals, the expected chemical shift for each type of protons (charts were provided), and the number of neighboring protons to assign the multiplicity. Then the students were instructed to compare these data with those obtained from the analysis of the spectrum. The students were advised to organize their thoughts, tabulate their findings, and eventually, write down their arguments. The table helped the students make the comparison more intuitively, and it was more convenient for them to evaluate each structure by comparing its data back to the data from the spectrum. Most students chose the correct structure, but the reasoning of a few students was neither precise nor informative. This was likely due to difficulties in translating their thoughts into words. Using the charts of chemical shifts helped them to understand more clearly the effect of any adjacent functional group or multiple bonds on the value of chemical shift. All this was reflected in gradual improvements in their grades. Noticeably, their explanations became more perceptive. Organizing the abstracted data in tables also made it easier for the instructor to read and mark the students’ work relative to the disoriented and disorganized answers received before the method was applied. This set of problems with a gradual increase in the level of difficulty was intended to introduce the students progressively to self-discovery learning methodology before they were confronted with the unknown spectrum. Furthermore, the students in small cooperative groups, tackling with spectra of known structures and guided questions, were indirectly asked to use their conceptual knowledge of 1H NMR to solve the problems, therefore transforming them into active thinkers and continuous learners. Figure 1 demonstrates a sample of this type of problem where the students applied the stereochemical aspects of chemical shifts or coupling constants to assign the geometry of substituted alkenes. Other problems were given to solve the relative stereochemistry of cyclohexane derivatives or to
outcome, students drew an incorrect chemical structure of the compound or leave the fragments of the molecule unattached. Consequently, the exam grades were below the KAU required pass grade (60%). Therefore, the need for another learning method to help the students develop the skills necessary to solve problems of increasing complexity and become capable of identifying the chemical structure of unknown compounds from their 1H NMR spectra was called for. An approach that proved to be effective to help the students digest the fundamentals of 1H NMR spectroscopy and involve them in a thoughtful learning of the regular course contents is to introduce, systematically, an atmosphere of thoughtfulness to the classroom. This is accomplished by means of simultaneous incorporation of thinking skills13 along with cooperative learning techniques into the1H NMR class.14−16 The approach is called “skillful thinking approach” and is based on teaching the students “how to think” by coaching them on how to use effective skills such as data analysis, problem solving, scientific argumentation and critical/creative thinking to explain concepts, interpret spectral data, and eventually, be able to evaluate and criticize various solutions.17−20 This study was designed to accommodate third- and fourthyear chemistry major students with a wide spectrum of student comprehension and intellectual levels. It was introduced in a 90 min-class with an average of 12−15 students, ages 21−25 years, over three consecutive years. The method created a class atmosphere that encouraged students to ask questions, analyze and correlate spectral data and, therefore, develop their skills of problem solving. Moreover, it contributed to their ability to work collaboratively and initiate peer discussions, which added richness and depth to their learning. As a result, the students were able to construct and assemble various structural fragments of the unknown organic compound and evaluate the possible chemical structures. Ultimately, they could choose the best answer of the problem in hand.
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OVERVIEW OF THE COURSE STRUCTURE The 1H NMR contents were gradually introduced to the students. This was done by training them on signal recognition and teaching them that each signal represents a fragment of the molecule and how to infer that fragment from its signals in the spectrum using the strategy of breaking the problem into smaller ones. This strategy was used in other studies.8,19,21 Then, problems with varying levels of difficulty were employed to allow a smooth progression of student learning ability using simple spectra with known chemical structures to more complicated spectra of unknown compounds. During the preliminary stages, the students were provided with some help from the professor or the lab teaching assistant until they could develop the required skills to solve an unknown spectrum. First, a brief introduction to the 1H NMR concepts was given to the students, followed by a 15 min quiz. The quiz consisted of a 1H NMR spectrum supplemented with the structure of its organic compound and a list of questions to stimulate their thinking. The intent was to guide the students to discover the principal concepts of 1H NMR before they were extensively exposed to this information by the professor. The majority of the students were able to assign the number of different types of protons in the structure and correlate it to the number of signals in the spectrum. In other problems where the number of signals is less than the number of different groups of protons, most of the students realized that the missing signal was due to an exchangeable proton. Using the same quiz to facilitate the B
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Figure 1. Sample of a student’s answer to a problem.
the spectrum nor did they actually put together a complete structure, which resulted in a tremendous drop in their grades. So, working through the questions in the thinking map (Figure 3) actually helped them to explicitly organize their thoughts and put effort into deeply thinking about the nature of the spectral problem (as demonstrated in Figure 4). In the proceeding stage (25 min period), thinking actively, the students were instructed to systematically engage the course content by using a graphic organizer (Figure 4).13 It is another helpful instructional tool that was used as a guide to the strategy of problem solving. It helped the students to transfer the spectral information methodically from their memory and apply it to def ine the spectral problem comprehensively. Before using the graphic organizer (Figure 4), some students identified the problem as analyzing each signal in the spectrum separately in terms of multiplicity/coupling constant and chemical shift and solved the problem accordingly, overlooking the requirement for elucidating the chemical structure. A few students put substructures without connecting them. Others were blank; they did not know what it meant by a spectrum of an unknown organic compound given solely with a molecular formula. Nonetheless, with the aid of the graphic organizer along with some helpful tips from the professor, the students were given the chance to discover what the 1H NMR problem was and how it can be solved. Also, communicating with their peers helped them to realize their mistakes. Ultimately, the students were able to list the facts about the problem, such as what spectral data they were provided with, what Supporting Information was given to them, and so on. Subsequently, they were able to record the purposes and needs to solve it as shown in Figure 4. The best statement for the problem that will accomplish all the needs listed was chosen and written down. By analyzing each groups’ graphic organizer, it was evident that the students were capable of achieving this stage successfully and, more importantly, they began to think skillfully and actively on how the spectral data function and how they can manipulate it to solve the problem and assign the chemical structure.
determine the proximity of certain protons in various types of organic molecules such as aromatic compounds.
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IMPLEMENTATION OF PROBLEM SOLVING SKILLS INTO 1H NMR SPECTROSCOPY CONTENT As the semester proceeded, a 1H NMR spectrum of an unknown organic compound along with tables of 1H chemical shifts and coupling constants were given to each group, and they were asked to work collaboratively and solve the spectrum and elucidate the structure of the compound. This is the most difficult task to perform in 1H NMR spectroscopy class. By approaching this stage, the students were eager to solve the unknown compound, and this observation had not been recorded before the method was used. Before they started to work on the spectrum, the students were coached to apply the problem solving skill to interpret the 1 H NMR spectra by using a multistep lesson plan (Figure 2). This was introduced in a 90 min period and required the instructor to restructure the lesson content in order to reinforce the skill.13 In the first stage of the lesson plan (Figure 2) and during a 15 min period, students were introduced to the skill of problem solving by relating this thinking skill to their own experiences, that is, everyday problems and cases remote from the learning environment in an effort to make the lesson more substantive and effective. They were prompted to ask a series of questions and were stimulated to use an organized strategy and list these questions in the form of a thinking map (Figure 3).13 They were encouraged to use this map as a window into their minds to reflect the way they think and to assist them realize that a problem did exist and how they can caref ully identif y it. Using the thinking map (Figure 3) appeared to be very useful in the proceeding stage. Defining the problem in 1H NMR spectroscopy class is a crucial step and it represented a major obstacle to the students in the past. Too often during solving a spectrum of an unknown compound (in class or exams), the students did not understand the question and did not know how to answer it. Consequently, they could not fully interpret C
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Figure 2. Infusion lesson plan of skillful problem solving. (Adapted from ref 13, used with permission.)
in an effort to construct a group of spin systems with the least amount of errors. The spin systems were then connected and any missing heteroatom, when compared to the molecular formula, was added with regard to the chemical shift of the attached protons. Some groups attempted to build more than one possible structure and any irrationalized structural features were reconsidered, and the structure that was most consistent with the data was chosen. Those students were asked to explain their answers on the board to teach their peers the logic of their solution. The only drawback is that they took more time than others. Toward the end of the course and with more complex problems given, the majority of the class demonstrated an improved understanding of the course content. In addition, they acquired the skill of problem solving and used it more competently to interpret the spectra. Their communication became more productive and more methodical which was reflected as better course grades.
Figure 3. Thinking map of skillful problem solving. (Adapted from ref 13, used with permission.)
Moving on to solve the spectrum, they were given a 50 min period, during which each group had the chance to abstract data from the spectrum, analyze it, and explain their reasoning in writing. They practiced scientific arguments under the supervision of their professor and each member pursued her own thoughts and assessed them against her peers while the activity and performance of each group was monitored. This stage was concluded by opening a free discussion with the professor. Figure 5 illustrates a sample of students reasoning and answers to the 1H NMR problem. From the students’ reported comments (Figure 5), it was possible to gather each group’s reasoning and analysis of the spectral data. The majority of the students drew the correct structure without showing every single step of their argument and their grades were below average. A few were thorough in their reasoning. These groups analyzed integration, chemical shift and multiplicity for each signal and tried to correlate those signals having the same coupling constant in a sort of a network
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ASSESSMENT OF THE STUDENT WORK AND EVALUATION OF THE METHOD The impact of the approach on student learning and the assessment was done using two evaluation methods. One tool was grading their quizzes and exams (interpretation of spectra). The standards used for the evaluation, such as pointing out the important parts to be evaluated and the scoring system, were all explained to them prior to exams.22 The results were then compared with those in which the approach was not applied for three consecutive years. The other method used to gather evidence as to what extent the students think they have learned about 1H NMR over the entire semester using this approach is the student survey data. D
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Figure 4. Sample of a student’s graphic organizer of skillful problem solving. (Adapted from ref 13, used with permission.)
Figure 5. Sample of a student’s analysis and solution of the unknown problem.
separately, we obtained the following findings: in 2010, the mean value for method 2 was higher (74.00; number of students = 7) than that for method 1 (65.46; number of students = 13). The trend continues for year 2011, as it shows a mean value of 76.30 (number of students = 10) for method 2 relative to 62.80 (number of students = 9) for method 1. In year 2012, a significant difference was detected in students’
Analysis of the statistical data between year 2010 and 2012 for method 2, in which the approach was implemented in class versus the traditional method, method 1, reveals a comparative statistical difference in students’ performances as it is apparent from the improvement rate in the scores when method 2 is used. When applying the independent samples t-test to compare the results between method 2 and method 1 for each year E
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performance as the mean value for method 2 was 78.33 (number of students = 7) and that for method 1 was 57.14 (number of students = 21), as can be seen from the bar chart (Figure 6).
Box 1. Students’ Survey of the Approach in Solving 1H NMR Spectrum ASSESSING STUDENT LEARNING; THINK ABOUT THINKING Interpretation of 1 H NMR Spectrum of Unknown Compounds by Applying Problem Solving/Collaborative Learning Skill 1 Did working in groups help you understand 1H NMR and solve the spectrum? • Interaction with my peer helped me better understand • It made me realize my mistakes and correct them • It confused me more • I prefer to work alone 2 Did applying problem solving skill help you to • Identify the spectral problem • How to use tables of spectral data • Abstract the contents of a spectrum and interpret them • Solve the structure of the unknown • Was unhelpful 3 Did the method help you in • Learn more in class or Prefer study alone at home • Participate in class or Prefer to listen to your professor 4 What are the disadvantages of the method: • Complicated • Confusing • Take long time • Not useful 5 Was the method effective? Will you used it again in the spectroscopy course? 6 Will you be able to use it in another course? 7 If you have any comments or suggestions you would like to add, please do so in the space below!
Figure 6. Bar chart for comparing the two methods across time.
Conducting the independent samples t-test for both methods regardless of the time (mean 2 = 76.33; mean1 = 60.64) shows a p value
