Article pubs.acs.org/jchemeduc
The Use and Evaluation of Scaffolding, Student Centered-Learning, Behaviorism, and Constructivism To Teach Nuclear Magnetic Resonance and IR Spectroscopy in a Two-Semester Organic Chemistry Course Kimberly Livengood,† Denver W. Lewallen,‡ Jennifer Leatherman,‡ and Janet L. Maxwell‡,* †
Department of Curriculum and Instruction and ‡Department of Chemistry and Biochemistry, Angelo State University, San Angelo, Texas 76909, United States S Supporting Information *
ABSTRACT: Since 2002, infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectrometry have been introduced at the beginning of the first-semester organic chemistry lab course at this university. Starting in 2008, each individual student was given 20 unique homework problems that consisted of multiple-choice 1H NMR and IR problems during the firstsemester course and a combination of 1H NMR, 13C NMR, and IR during the second-semester course. Using the four instructional techniques of scaffolding, student centered-learning, behaviorism, and constructivism, students were assisted in solving these homework problems by the instructor and a small group of upper-level students. A comparison was made of exam data from years in which students shared a small variety of homework assignments versus years in which each student had his or her own unique set Used with permission from Sigma-Aldrich. of homework problems. The data indicate that solving the unique problems with assistance from tutors provides an effective way for the students to learn the difficult topics of NMR and IR spectroscopy. KEYWORDS: Second-Year Undergraduate, Curriculum, Laboratory Instruction, Organic Chemistry, IR Spectroscopy, Learning Theories, NMR Spectroscopy, Student-Centered Learning, Molecular Properties/Structure contained duplicate problems. The students still seemed to find other students with the same homework questions, allowing them to copy answers from each other. It became obvious that each student needed to have a completely different set of 20 spectroscopy problems of the appropriate difficulty each semester for them to learn to interpret spectra effectively. A survey of the current editions of organic chemistry textbooks in the United States shows that the topic of spectroscopy, including infrared (IR), nuclear magnetic resonance (NMR), UV−visible, and mass spectroscopy, appears in later chapters of the textbooks, typically in chapters ranging from 12 to 14 so that professors present this subject matter in the second semester of the course (see the table in the Supporting Information). Presumably, professors and textbook authors wait until the second-semester organic chemistry course to introduce spectroscopy so that students have a strong grasp of the common structural units and the relationship between different functional groups in organic compounds. In the past decade or so, the Solomons and Fryhle text3 has introduced infrared spectroscopy in Chapter 2 and other common spectroscopic methods in Chapter 9. The extended amount of time over the two-semester course as a
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he study of spectroscopy is an important topic in collegelevel organic chemistry courses. Spectroscopy can be taught using a number of different strategies.1 In the summer semester of 2002, one of the authors (J.L.M.) embarked on an endeavor to find a way to teach spectroscopy effectively at a medium-sized state institution. Spectroscopy was introduced in the laboratory sessions of the second-semester course that first summer. This attempt involved about 9 h of pure lecture and a group of 10 homework problems, with all students receiving the same set of problems. Each spectroscopy problem consisted of two spectra for the same compound: one IR and one 1H NMR spectra. Students were expected to solve the structure of each compound. This strategy proved to be an ineffective way to teach the material because the students simply copied each other’s answers and failed to learn the material, as evidenced by low exam scores. Over the next several years, the number of problems given to each student was increased and a larger variety of spectroscopy homework problems were developed (∼250 NMR spectra and ∼200 IR spectra) mostly selected from the Sadtler spectral library.2 Choosing a large number of spectra that were not too difficult or too simple from the random assortment found in Sadtler binders proved to be particularly problematic. Using this system, the students’ homework packets varied somewhat, although many packets © 2012 American Chemical Society and Division of Chemical Education, Inc.
Published: June 8, 2012 1001
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students’ own way of thinking. This places the responsibility for learning on the student, but also empowers the student to learn in the manner that is most effective for him or her. The 20 different spectroscopy problems and assistance provided to each student individually results in student-centered learning with the scaffolding described in the previous paragraph. The third, and perhaps most basic of the three educational strategies employed in the beginning of this project, is behaviorism. Behaviorism is a branch of psychology that posits the idea that the learning of behaviors, skills, and concepts is accomplished by a process called conditioning. From the perspective of the instructor, operant conditioning includes identifying the objective in measurable terms prior to learning, teaching the lesson in small incremental steps, and continuously providing feedback or reinforcement as needed.13 Classical conditioning, a very basic teaching and learning technique, was initially employed to teach spectroscopy. First, the students were presented with the visual stimulus, in this case absorptions or signals in the IR or NMR spectrum of various known compounds. Second, the students were exposed to the same stimulus, the same types of signals previously seen in the known spectra, this time within the unknown spectra given as homework problems. The determination of the identity or cause of a single peak or absorbance from the unknown spectrum forms the neutral response. The positive reinforcement is the confirmation of the correct determination from an instructor or tutor. Eventually, after some repetition of this process, the neutral response, identification of a peak, becomes associated with the positive reinforcement of answering correctly because of the student’s ability to determine accuracy on his or her own. To summarize the first-semester course, the educational techniques employed in teaching spectroscopy with the use of the homework problems were scaffolding, student-centered learning, and behaviorism.14 At the end of the first-semester course, students had been exposed to not only the principles of determining the structure of organic compounds, but also the basic applications of using IR and 1H NMR spectroscopy to identify the correct structure from a group of four multiplechoice answers. During the second-semester course, the goal was to convert the students’ preliminary understanding of spectroscopy from the first semester to the more intricate skill of solving the structure of organic compounds by analysis of IR, 1H NMR, or 13 C NMR spectra. The use of the three educational strategies listed in the previous paragraphs continued into the second semester, but the 20 problems were significantly more complex and involved complete identification of organic compounds through the use of two of the three spectroscopy techniques along with the given molecular formula for each compound. As the semester progressed, the strategy of behaviorism was replaced by constructivism. According to the cognitive research, students must move beyond the behaviorist response to understand the complexity of a concept.15 The constructivist approach requires the instructor to build or construct on the students’ prior knowledge.16 The first-semester approach provided the students with sufficient prior knowledge for them to begin constructing their own understanding of the concepts of spectroscopy during the second semester with assistance from the tutors and the professor.
result of this earlier introduction of spectroscopy would provide the students the opportunity to effectively learn this complex and crucial concept and allow the textbook authors to present spectroscopic applications of the identification of each class or family of organic compounds in the appropriate chapters.3 As of the completion of our textbook survey, none of the other major authors of organic chemistry textbooks have followed Solomons’ lead. This author (J.L.M.) was concerned with the limited time students had to learn spectroscopy when presented in the second-semester course. Thus, in the fall of 2002 and in subsequent years, both IR spectroscopy and proton NMR spectrometry were introduced in the lab course the first week of the first semester. In the first-semester course, students were given 20 homework problems consisting of an IR spectrum or 1 H NMR spectrum, each having four multiple-choice answers.4 During the second-semester course, students were given 20 homework problems consisting of a molecular formula and two spectra for the same compound: either one IR and one 1H NMR spectrum or one 1H NMR and one 13C NMR spectrum.4 Students in the second-semester course were expected to solve the structure of each compound.
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RATIONALE At the beginning of the first-semester organic chemistry course, students lack a solid grasp of the fundamentals of the structures of organic compounds. The idea of teaching spectroscopy at this point in time comes from the educational strategy called scaffolding. “The zone of proximal development is the distance between what [students] can do by themselves and the next learning that they can be helped to achieve with competent assistance”.5 When instructors scaffold instruction, the students participate in activities that are initially beyond their skill and knowledge.6,7 The instructor provides the scaffold or steps so that the learner is able to complete the required task with assistance until the student has developed the necessary understanding to learn the concept. This assistance guides the students through the zone of proximal development.8 The initial exposure to the concept then provides the necessary prior knowledge for the students to more quickly and effectively learn the concept and take it one step further.9 In research, scaffolding strategies have resulted in positive outcomes in student learning.10 This process of scaffolding involved teaching IR and 1H NMR at an introductory level to the students before they could obtain a complete understanding of the structure of organic compounds, but in such a way that the students were exposed to the concepts over a greater period of time. Although the students learn spectroscopy and organic structure at the same time, they are not expected to master the spectroscopy concepts until they are retaught during the second semester. Theoretically, the students should learn the information more effectively than if the concepts are only taught once.9 Student-centered learning was also employed as a way to help students learn in this situation. The students’ prior experiences and prior knowledge contribute to their perceptions as they learn.11 With the use of exclusive homework assignments for each student to complete with assistance from the instructor and upper-level students acting as tutors, the emphasis was placed on each student’s initial understandings. These understandings included misconceptions because those influence how the student learns the content.12 Rather than teaching the material using only the one traditional method, the professor and tutors focused on the 1002
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Table 1. Types of Compounds Used for the 20 Assignments for First and Second Semesters Types of Compounds Nonaromatic hydrocarbons and halogenated hydrocarbons Nonaromatic alcohols, ethers, epoxides, acetals, and amines Nonaromatic ketones, aldehydes, acids, esters, lactones, acid halides, anhydrides, and amides Aromatic hydrocarbons and halogenated hydrocarbons Aromatic alcohols, ethers, epoxides, acetals, and amines Aromatic ketones, aldehydes, acids, esters, lactones, acid halides, anhydrides and amides Alkynes Miscellaneous
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H NMR (multiple choice) n = 830
IR/1H NMR n = 720
18.1% 13.5% 14.9%
20.8% 10.6% 13.8%
23.1% 23.9% 11.1%
18.9% 20.0% 23.8%
7.9% 16.7% 25.1%
8.3% 16.6% 26.1%
4.2% 21.9% 13.2%
10.1% 14.5% 9.4%
3.8% 0.0%
3.8% 0.0%
1.8% 0.8%
3.1% 0.2%
IR (multiple choice) n = 830
METHODOLOGY By using the first three educational strategies described in the rationale section, both infrared spectroscopy and proton nuclear magnetic spectrometry were introduced during the first week of the first semester of the organic chemistry course starting in the fall of 2002. During that first semester, about 6 h of interactive lecture covered both IR and 1H NMR over a three-week period in the laboratory section of the class. The lecture focused mainly on an introduction to the applications of using spectroscopy to determine information about the structure of unknown compounds. The students were given a 60-page module covering infrared spectroscopy and a 40-page module covering introductory proton nuclear magnetic spectrometry, both of which were developed by the author (J.L.M.) and evolved over the nine-year period of this study (outlines of the modules are available in the Supporting Information). The IR module includes a brief discussion of the theory of IR spectroscopy. Both first-semester modules focus on the types of information gained from an IR or 1H NMR spectrum, with detailed visual or tabular signal charts and many examples of known spectra. An emphasis is placed on pattern recognition in the shape and location of signals. The main goal of these first-semester modules is to provide a reference to the students for peak recognition rather than to explain the theory of spectroscopy. The lecture and reading material supplemented the main instructional technique that consisted of the use of the 20 homework problems given to each student. The spectroscopy homework problems given for the first semester consisted solely of multiple-choice exercises in which students identified and utilized many of the concepts of spectroscopy without combining them to solve a structure. For the IR assignment, students were asked to identify functional groups responsible for the major IR absorptions, circle the correct structure of the four possible structures, and write a brief paragraph explaining the reasoning. For the 1H NMR assignment, the students were asked to make a complete NMR correlation chart, circle the correct structure and explain their reasoning. Each student received 10 IR and 10 NMR spectra. From 2002 until 2007, these problems came from a pool of 200−250 problems. Starting in the fall semester of 2008, enough problems had been compiled using an electronic database for each student in the course to be assigned 20 unique problems. Because no student had a single homework problem in common with another student, students were unable to copy each other’s answers. They determined an answer based on their own knowledge or with unique individual attention from the professor or tutors. A number of different free tutoring sessions, both at the departmental and university level, were provided. Tutors were selected or
1
1
H NMR/13C NMR n = 720
recommended by the instructor based on grades in the organic course, social skills, and verbal ability. Both the departmenthired and university-hired tutors had a copy of the answers to all the spectroscopy homework problems to check the students’ answers. The professor and tutors played an important role in the scaffolding process by providing homework assistance to the students. Those taking part in the instruction process, both instructor and tutors, must have a clear understanding of the content and the level of scaffolding needed to effectively guide a student’s learning.17 The tutors were instructed to allow the student to take the lead in the problem-solving process. By this method, tutors roughly assessed the level of each student’s skill while the students applied the concepts learned independently and obtained help with concepts when needed. Students learn more effectively when guided through the zone of proximal development to the next level.18 The first-semester lab exam consisted of ∼35% spectroscopy and ∼65% other lab topics. The student learning outcomes of IR and 1H NMR spectroscopy were tested during the firstsemester course on a group of five multiple-choice questions on the end-of-semester lab exam. The multiple-choice format of the first-semester final supported the behaviorist perspective as students focused on the “pieces” in the beginning instead of the “big picture”.12 In this case, the “pieces” refer to the discrete signals or absorptions as they were used to identify individual functional groups or regions of the molecule, whereas the “big picture” was the entire spectrum as it is used to identify the complete structure of the compound. Students did not need to have a comprehensive understanding of how spectroscopy is used to determine structures to correctly answer a multiplechoice problem of this type. Students were able to determine the correct multiple-choice answers using simple classical conditioning based on accurate identification of only a portion of the molecule as long as incorrect answers were ruled out. Thus, a good foundation for learning spectroscopy was laid during the first semester, but the learning process was incomplete at this point. Second-semester coverage of spectroscopy began the first week of the semester starting in the spring semester of 2003. Before the second-semester problems were assigned, another time period of 6−8 h in the lab course was spent providing spectroscopy instruction to the students. Students were given the same infrared spectroscopy module from the first semester and an extended nuclear magnetic resonance spectrometry module that included basic NMR theory, pulse Fourier transform NMR theory, an explanation of enantiotopic and diastereotopic protons, coupling constants, two-dimensional 1H NMR, and the theory and application of 13C NMR. The goal of the instructor during the second-semester course was for 1003
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Table 2. Three Versions of Tests Given for the Second Semester Lab Final (2007−2011) Test Version
IR/1H NMR
IR/1H NMR
1
1 2 3
m-methylacetanilide m-aminoethyl benzoate o-ethoxybenzamide
3-phenylbutanal 2,2-dimethyl-1-phenyl-1-propanol 2-methyl-3-phenylpropanal
IR/1H NMR/13C NMR
3-methylbutyl ethanoate (E)-2-hexene 1,3-dibromobutane
p-(1,1-dimethyl-propyl)phenol 4-(p-hydroxy-phenyl)-2-butanone p-butylbenzyl alcohol
first attempt were allowed a second attempt, but that data has been omitted from our analysis. Our results indicate that in summer 2002, spring 2003, and spring 2005, the percentage of students failing the exam was 58.8% (n = 17), 76.2% (n = 42) and 34.0% (n = 47), respectively. In 2007, 28.0% of the students failed the spectroscopy exam (n = 50). The following year with the larger variety of spectroscopy homework problems from the online databases, only ∼7% of the students failed the exam (n = 54). The trend continued with only ∼6% (n = 63) of the students failing the exam in 2009 and only ∼3% (n = 69) of the students failing in 2010. In 2011, ∼8% of the students failed (n = 49). The spring and summer semester data for the same years have been combined. Figure 1 shows the
students to understand both the theory and the complete application of spectroscopy for structure determination. Two new packets of homework assignments were given, providing each student with 10 unique IR/1H NMR problems and 10 1H NMR/13C NMR problems. The IR/1H NMR and 1H NMR/13C NMR problems were available in a large variety for the first time in the spring of 2008 and in the spring of 2009, respectively. For both second-semester assignments, students were required to calculate the index of hydrogen deficiency from the given molecular formula, identify important peaks in the IR spectrum if applicable, show correlation charts for all NMR spectra, draw the structural formula of the compound, and show which protons correlate to which peaks in the 1H NMR spectrum. In designing the homework problems both semesters, an effort was made to put together a wide array of compounds with different functional groups using spectra from the Spectral Viewer software.19 The core idea was that the 10 problems from each major set offered each student a good variety of different problems for the applications of diverse strategies to solve for the correct structures. Table 1 gives the percent distribution of the types of compounds divided into categories. Note that many of the structures are multifunctional. In that case, the compound was typically assigned to the category representing the functional group with the highest nomenclature priority.
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H NMR/13C NMR
ASSESSMENT
The second-semester “spectroscopy exam” assessed the learning outcomes of understanding the basic theory of IR and NMR spectroscopy and being able to solve structures with the use of two spectra for the same compound given the molecular formula. Typically given about halfway through the second-semester organic chemistry course, this exam consisted of 20% theory and 80% solving structures. Although the exam differed somewhat from 2002 until 2011, an effort was made to keep the questions the same or very similar throughout the years. Table 2 lists the structures to be solved on the exam for several years. Exam security was maintained by only allowing students to look at their graded exams individually or in small groups in the instructor’s office. To solve the structures from Table 2 using a combination of spectra and molecular formula, students must employ more complex problem-solving skills than those needed for the firstsemester multiple-choice spectroscopy questions. To consistently solve the problems on the spectroscopy exam correctly, the students must build on the initial behaviorist response. Students must combine the skill of recognizing individual peaks or absorptions developed using the classical conditioning approach with the newly learned understanding of the theory of spectroscopy to construct a general problem-solving strategy for structure determination. This synthesis of knowledge and skills to solve more complex problems is a hallmark of the constructivist approach to learning. To pass the spectroscopy exam, the students must obtain a score of 70% or better. Students who failed the exam on the
Figure 1. Correlation of test grades with the implementation of teaching technique.
relative percentage of the number of students who passed versus those who failed for the entire term of the study from 2002−2011. Table 3 shows the distribution of the grades. A dramatic change in this data can be seen in the years between 2007 and 2008. The spring semester of 2008 is the first semester in which a portion of the new homework problems was assigned. Although the spring and summer 2008 classes had been exposed to the “old” Sadtler problems first semester, these groups did have a unique set of IR/NMR assignments for the second-semester course. By the fall of 2008 in time for the spring/summer 2009 classes, enough of all the new assignments were available so that each student had 20 unique problems both first and second semester. As our student population continued to grow, new assignments for all the students were developed. Table 4 shows the t test results from a comparison of the exam score data from 2002 until 2010. The exam scores from any year prior to 2008 are statistically different from the exam scores from any year in the 2008−2010 range. The exam scores from any two years prior to 2008 are statistically similar to each 1004
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Table 3. Percentages of Grades for Semesters Ranging from 0 to 100 Percentages of grades Ranging from 0 to100 Implementation Initial system of problems
Introduction of new IR/1H NMR problems second semester Introduction of all the other new problem sets
Semester
0−49
50−59
60−69
70−79
80−89
90−100
Totals
Summer 2002 (n = 17) Spring 2003 (n = 42) Spring 2005 (n = 47) Spring 2007 (n = 50) Spring/Summer 2008 (n = 54)
35.29 35.71 21.28 18.00 3.70
11.76 14.29 12.77 4.00 3.70
11.76 26.19 0.00 6.00 0.00
5.88 14.29 23.40 26.00 24.07
11.76 4.76 19.15 20.00 24.07
23.53 4.76 23.40 26.00 44.44
100.00 100.00 100.00 100.00 100.00
Spring/Summer 2009 (n = 63) Spring/Summer 2010 (n = 69)
4.76 1.45
1.59 1.45
0.00 0.00
25.40 28.99
38.10 27.54
30.16 40.58
100.00 100.00
finding the answer and not being able to apply that knowledge to a later spectroscopy question.” Another student summarized the entire experience, “I would attempt a problem and after coming to a standstill, I would be able to obtain assistance. I was never given a complete answer, but instead, I was walked through the learning process by somebody who had more experience in the subject. This was critical in allowing me to learn effectively”.
Table 4. Statistical Analysis of Grades in Years Teaching the Technique versus Years Teaching Technique Was Not Implemented Statistical t-Test Results of Exam Score Data from 2002 until 2011 Year vs Year Method Used
t Test Calculated
t Table Value
2002 vs 2008
6.59
2.00
2002 vs 2009
4.17
2.00
2002 vs 2010
4.97
2.00
2003 vs 2008
6.72
1.98
2003 vs 2009
7.81
1.98
2003 vs 2010
9.04
1.98
2005 vs 2008
3.17
1.98
2005 vs 2009
3.25
1.98
2005 vs 2010
4.20
1.98
2007 vs 2008
2.37
1.98
2007 vs 2009
2.24
1.98
2007 vs 2010
3.14
1.98
2008 vs 2009
0.73
1.98
2008 vs 2010
0.12
1.98
2009 vs 2010
1.15
1.98
Comparison t test > table t test > table t test > table t test > table t test > table t test > table t test > table t test > table t test > table t test > table t test>t table t test>t table t test
