In the Classroom
Two-Cycle Organic Chemistry and the Student-Designed Research Lab Dennis J. Gravert Department of Chemistry, Saint Mary’s University of Minnesota, Winona, MN 55987;
[email protected] Students often regard organic chemistry as one of the most difficult college courses (1), and instructors have responded to this perception by developing more effective pedagogy, such as prelecture assignments (2, 3), lecture aids (4, 5), learning cycles (6, 7), collaborative learning (8–11), active learning (12–15), and peer-led team learning (16). Also successful are curricular changes that reorganize the presentation of topics, a strategy called “two-cycle” organic chemistry (17, 18). In this approach, the first semester consists of a survey of the fundamentals of organic chemistry, highlighting the major topics of a full two-semester sequence of courses. In the second semester, discussion of topics is expanded such that the total quantity of material covered in the two-cycle approach is equivalent to that of the traditional yearlong course. In similar fashion, a novel curricular change to reorder the topics between the two courses of organic chemistry and biochemistry has been proposed by Reingold (19). As indicated previously (17–19), the reorganization of topics through a two-cycle strategy has many advantages over the traditional organization of full-year organic chemistry courses. Realizing that most students of organic chemistry are not chemistry majors (20), the benefits include (i) earlier discussions of the organic chemistry of biopolymers, including proteins, carbohydrates, and nucleic acids, (ii) additional opportunities to emphasize connections between biology and chemistry, (iii) directed review and relearning of fundamental concepts, (iv) exposure to a wider range of topics for biology students who take only one semester of the course, and (v) more focused attention on the intricacies of organic chemistry with a smaller number of students during the second semester. While the curricular change is more useful and relevant to the nonchemists, chemistry students benefit as well, perhaps most significantly during the second semester, which provides in essence a second chance to learn organic chemistry more completely. Three years ago at Saint Mary’s University of Minnesota, a two-cycle strategy was implemented for several reasons. At that time, the change to a laboratory format in which organic chemistry students independently design and execute synthetic research projects (21–24) was under consideration. These projects involve a student choosing any molecule desired (within reason!), planning the multistep synthesis of the target molecule, and executing the plan in the laboratory. These projects have proven to be effective learning experiences; however, there is a major limitation given the traditional lecture course. In order to propose a multistep synthetic scheme that possesses a reasonable chance for success and an appealing target molecule, a student must know a considerable quantity of organic chemistry. But to delay the task of investigation until after such knowledge is acquired would leave little time in the course to complete the research! To provide ample time to work on projects, a strategy was needed to enable students to quickly learn a broad set of reactions early in the two-semester sequence of organic chemistry. In effect, the students 898
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required a survey course. The need for a survey course was recognized earlier, but for a different reason. It is very difficult for many undergraduates to complete some specialized science programs (e.g., nursing, environmental biology, etc.) in four years owing to a large number of required courses. Students in these programs might be better served by completing a one-semester survey course in organic chemistry rather than the standard two-semester sequence. The desire to teach such a course has persisted for many years; however, current teaching loads prohibited offering it. The two-cycle strategy for teaching organic chemistry was adopted in response to these two challenges, (i) to rapidly prepare students to design synthetic research projects and (ii) to provide a survey course without increasing the teaching load. Implementation of the two-cycle strategy at Saint Mary’s differs from previously published versions (17, 18) in that one textbook, not two, is used over the two semesters. In the original two-cycle approach, students in the firstsemester course purchase a textbook written for short courses, and then in the following semester they purchase a second textbook designed for two semesters of organic chemistry. A common complaint of many students (in addition to the higher expenditure for textbooks) is the lack of detail in the short text (18). Upon acquiring the full textbook, students find the short text has limited value. Instead, our students purchase a comprehensive, two-semester textbook at the beginning of the first semester. Detailed syllabi and frequent announcements (in the classroom and through the online course management system) guide the students to use a single textbook for both semesters of organic chemistry. Survey Course for the First Semester Before we adopted the two-cycle strategy, topics were presented in sequential order as they appeared in the course textbook.1 Hence, it was not until late in the second semester that carboxylic acids and derivatives (acyl chlorides, acid anhydrides, esters, and amides) were discussed. It was disappointing that students, especially biology majors, had to wait so long before discovering the chemistry of the peptide (amide) bond! Under the two-cycle strategy, the course content for the first semester consisted of a critical set of topics selected from the entire year of the traditional course. Through selective reading assignments, carefully chosen textbook problems, and recurring classroom and electronic announcements, students were directed to skim through the textbook to learn a specific group of key concepts and reactions. By skipping a few chapters and selectively reducing coverage of content from each chapter, students were able to progress through the textbook to reach the same final chapter as those students who had taken a one-year course, but in half the time. Thus by the end of the first semester, students had essentially completed a survey course in organic chemistry.
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In the Classroom
Choosing which topics to postpone until second semester was difficult, but time constraints demanded that it be done. For the most part, content was reduced by simply presenting a subset of reactions from each chapter (for example, Table 1 lists topics contained in the chapter of alkene reactions). The chosen subset included reactions that promoted continuity among chapters, such as the halogenation of alkenes whose products could be used as starting materials for the synthesis of alkynes, a reaction discussed in a later chapter. Also retained in this subset were those reactions that students might actually perform in their synthetic research projects, such as the dehydration of alcohols to form alkenes, rather than reactions requiring highly toxic materials (osmium-catalyzed oxidation of alkenes) or unavailable equipment (ozonolysis). Furthermore, it was helpful in the selection process to review homework problems assigned from the textbook as some questions required students to recall certain topics from preceding chapters: these prerequisite topics were included or the homework problem was thrown out. Unfortunately, a few chapters had to be delayed entirely. The chapter headings for topics omitted during the first pass through the textbook are in List 1. The deferment of a few topics, such as chirality and stereochemistry, could be justified because some discussion had taken place in a preceding course of general chemistry. Other topics, although their corresponding chapters were not assigned reading, found their way into classroom discussions during the first semester at opportune times. For example, the chapter on substitution and elimination reactions was skipped; however, the SN1, SN2, E1, and E2 mechanisms were introduced during discussions of the synthesis of alkyl halides from alcohols (SN1, SN2) and the synthesis of alkenes (E1, E2). Finally some topics, such as aromaticity and alkane and cycloalkane conformations, were set aside so that more time could be devoted to a greater number of reactions, which potentially could be utilized in student-designed research projects. Table 1. Reorganization of the Chapter Pertaining to the Reactions of Alkenes Presented First Semester
Delayed until Second Semester
Hydrogenation
Free radical addition of HBr
Hydrogen halide addition
Acid-catalyzed hydration
Carbocation rearrangements
Oxymercuration–demercuration
Markovnikov’s rule
Hydroboration–oxidation
Halogen addition
Osmium-catalyzed oxidation
Vicinal halohydrins
Ozonolysis
Intro to organic synthesis
Epoxidation Carbene addition
List 1. Topics Postponed until Second Semester Alkane and cycloalkane conformations Chirality and stereochemistry Substitution and elimination reactions Conjugation Aromaticity Ethers and epoxides
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The deferred topics in List 1 is significantly different from Reingold’s list of delayed topics (19), which reflect our differences in course themes (project-based laboratory versus bioorganic chemistry). Even so, Reingold emphasized that his curricular change should be successful even with a different choice of topics to delay. Likewise, the two-cycle strategy is not dependent on the current set of deferred topics, and instructors who desire to implement the strategy should feel comfortable selecting different topics as they see fit. Since the laboratory experience is an integral part of the course, the lecture and laboratory components of the course were synchronized as much as possible during the first pass through the textbook. For example, when esters were discussed in class, the students were completing Fischer esterifications in lab. To keep the classroom discussions synchronized with lab activities, the chapters on spectroscopy were taken out of textbook sequence and presented earlier so that students understood the operation of infrared (IR) and nuclear magnetic resonance (NMR) spectrometers when using these instruments in lab to determine structures of unknown compounds. During the first semester, such exercises in structure elucidation provided the training in both instrument operation and spectra interpretation, so that later, students were capable of independently completing analyses required by their second-semester synthetic research projects. Other activities of the laboratory program in the first semester introduced students to the techniques of synthesis, purification, and characterization of organic compounds (see Table 1 in ref 22 ). In the final weeks of the first semester, the students, working alone or in small groups, wrote research proposals as described in ref 22, with the modification that an additional synthetic step was required (a minimum of three synthetic steps instead of two) since the two-cycle strategy provided for an increase in time available to work on laboratory projects. During the interim between semesters, chemicals and supplies were ordered so that students could initiate their research projects immediately at the beginning of the second semester. Expand the Knowledge during the Second Semester In the second semester, students were directed to start at the beginning of the textbook and read through it again. During this second pass through the textbook, class discussions focused on course material that was omitted during the first semester. No class time was spent for formal review of course material that was covered earlier; however, a previously studied reaction or concept was often used to introduce something new. For example, the reaction mechanism for halogen addition to alkenes was illustrated again and then compared to the mechanism of oxymercuration of alkenes as both involve the ring opening of three-membered heterocycles. Such brief reviews of first-semester topics provided students with a new opportunity to fully understand old material as well as to make connections to new topics. By dedicating most of the class time of the second semester to filling in the gaps of knowledge created during the first pass through the textbook, the two-semester course organized under the twocycle strategy contained the same quantity of course material as the traditionally organized, one-year sequence of organic chemistry.
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In the Classroom
Although class time facilitated some review, students were motivated to reconsider first-semester topics outside of the classroom because a thorough understanding of these topics was required in order to complete second-semester exams. Students were instructed that they were responsible for knowing all the material in each chapter as it was encountered during the second pass through the textbook. Homework assignments, quizzes, and exams provided opportunities to reinforce the understanding of both old and new topics. Visits with the instructor during office hours and evening review sessions enabled students to ask questions about any topic, whether it was covered first or second semester. In effect, the reshuffling of topics provided students with a second chance to learn organic chemistry (19). Unlike the traditionally-structured course in which students had seven weeks to complete their synthetic research projects (22), the two-cycle strategy provided students with a full semester to work on the laboratory projects that they designed during the first semester. The additional time allotted for research made it possible for students to choose some interesting and challenging molecules to synthesize (Figure 1). Students had various motives for selecting their target molecules. Some less-daring students simply chose a new starting material and proposed to sequence together familiar reactions encountered during the first semester of laboratory (e.g., 1, by Grignard, oxidation, and bromination reactions). Many students selected common pharmaceutical agents (e.g., Benadryl, 2). The chance to earn reward money inspired some students to work on synthetic challenges posted on the InnoCentive Web site (e.g., 3; ref 25 ). One advanced undergraduate studied the patent literature on Viagra and with the instructor’s assistance proposed a 5-step synthesis to a novel compound with a simi-
lar structure (4). Although no student has yet isolated their final target molecule, several have come close. Students have not expressed overt disappointment at this, most likely because their laboratory grade was determined largely on effort rather than laboratory success. Furthermore, they were warned in advance that “actual research is much like this project; that is, 90% of attempted reactions may be unsuccessful” (22). Assessment The standardized ACS Organic Chemistry Exam, version 1998,2 was administered in the final week of classes during the second semester to provide a basis for comparison of student performance before and after the implementation of the two-cycle strategy. Organic chemistry students in the first two years of this study (identified as 2001 and 2002 in Figure 2) completed a traditional, linear progression through the textbook and experienced a laboratory program based on solving puzzles (26–29). Students in the last two years of organic chemistry (2003 and 2004) made two passes through the textbook and carried out student-designed research projects in the lab. The average (mean) ACS raw scores were calculated for each class of students during these four academic years and were plotted with their corresponding class average (mean) ACT entrance exam composite scores (Figure 2). Although the mean ACT scores were not statistically different across all four years3 (one-way ANOVA, p < 0.05), the mean ACS Organic Exam score for the combined set of students in 2003 and 2004 was significantly higher than the mean score for the pooled set of students prior to curricular and laboratory reforms (t test for independent samples, p < 0.01). Small class sizes (Table 2) required that a statistical analysis be performed with combined sets of students.
N O
ACT Entrance Exam ACS Organic Exam
O 40
Br HCl
before double pass strategy
35
after double pass strategy
30 25
2
Score
1
20 15 10 5
OH
0 2001
3
2003
2004
Academic Year Figure 2. Class averages (means) of ACT composite scores and ACS Organic Exam raw scores listed by year of the second (spring) semester of organic chemistry.
O N HN
O
N
2002
Table 2. ACS Organic Exam Scores
S N
O O
Academic Year (Spring Semester)
Class Size
Class Mean Raw Score
Range of Raw Scores
2001
28
27.1
18–43
4
2002
22
26.5
14–40
Figure 1. Examples of target molecules chosen by students for synthesis.
2003
22
33.8
19–47
2004
31
30.2
16–51
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In the Classroom
It cannot be determined whether students were able to achieve higher exam scores owing to their experiences with the curricular change or the laboratory restructuring. Actually, each was made more effective by the other. The reordering of topics allowed students to work on more challenging lab projects for a longer period of time, and the synthetic projects allowed students to apply their classroom knowledge and reinforce their understanding of organic chemistry. On the other hand, additional factors contributing to student success must be recognized. The instructor’s own increased enthusiasm for the new organic chemistry course could have positively influenced students. Undergraduates openly expressed excitement about their laboratory projects, and this could have transferred into increased motivation to study and learn. Finally, the opportunities to review material during the second pass of the textbook may be essential: one student commented that she felt less anxiety in the second semester because she began the task of studying for each exam with the confidence that she already knew half the material. Conclusions The reordering of topics by application of the two-cycle strategy has achieved four goals. First, those students who enrolled only in the first semester of the course were exposed to a broad survey of organic chemistry, which included a large number of biologically relevant topics. Prior to the curricular change, students who experienced only one semester of organic chemistry never saw past the first half of the textbook. Second, the first semester (survey course) provided sufficient knowledge and training so that students were able to design and carry out synthetic research projects during the second semester. Third, the two-cycle strategy provided additional time for research, a full semester versus seven weeks (22), and enabled students to choose more challenging and interesting target molecules for synthesis (compare compounds listed in Figure 1 versus synthetic targets listed in ref 22 ). And finally, those students enrolled in both semesters had a second chance to learn course material more thoroughly. By including first-semester topics on second-semester exams, students had incentive to study much of the textbook a second time. Students who experienced the two-cycle strategy performed at a higher level on exams, and it is expected that they will retain a greater understanding of organic chemistry in the years following completion of the course. Acknowledgments Support for this work was provided by Saint Mary’s University of Minnesota and the National Science Foundation’s Course, Curriculum, and Laboratory Improvement program under grant DUE-9980670. Special thanks go to Kim Oren and the Office of Institutional Assessment at Saint Mary’s University for the statistical analysis of exam data. Notes 1. During the first three years of this study (academic years 2000–2003), the required textbook was McMurry, J. Organic Chemistry, 5th ed.; Brooks/Cole: Pacific Grove, CA, 2000. In the fall of 2003, the course textbook was changed to Carey, F. A. Organic Chemistry, 5th ed.; McGraw-Hill: Boston, 2003. 2. It has been reported that the 1998 version of the ACS Organic Chemistry Exam appeared on the World Wide Web from May
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2002 to December 2002. To reveal whether students at Saint Mary’s University had seen the online version, students were asked to complete an anonymous survey after the exam was administered. Among the questions soliciting information about test preparation, one question asked if students had studied from an ACS Organic Chemistry Exam. No student answered affirmatively. 3. Lacking a better measure of innate student ability and knowledge, ACT scores were used to ascertain whether student performance on organic chemistry exams improved as a result of the curricular and laboratory changes or as a consequence that a smarter set of students happened to take the course (a genuine concern given the small class sizes). However, statistical analysis of ACT scores indicated that the latter did not occur, and, in fact, the increase in test performance could be attributed to the curricular and laboratory changes.
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