In the Laboratory
Incorporating Guided-Inquiry Learning into the Organic Chemistry Laboratory Barbara A. Gaddis Science Learning Center, University of Colorado at Colorado Springs, Colorado Springs, CO 80918 Allen M. Schoffstall* Department of Chemistry, University of Colorado at Colorado Springs, Colorado Springs, CO 80918; *
[email protected] Conventional wisdom acknowledges that the science laboratory plays a critical role in undergraduate education. One group of authors has identified 1547 specific goals of laboratory work (1), which can be broadly grouped into these four categories: 1. Improving conceptual understanding by making abstract concepts more concrete 2. Developing science inquiry skills 3. Developing technical skills 4. Motivating student learning
In spite of the numerous goals that the laboratory curriculum is expected to achieve, there is little evidence to suggest that these goals are being attained. Too often students come out of the traditional chemistry laboratory with little more understanding than when they entered (2, 3). Why don’t students learn more in the laboratory? Several reasons have been proposed, including an over-emphasis on lower-order skills (3, 4), spending too much time trying to get the “right” answer (5), and performing too many trivial synthetic experiments that require little student thought (6). These problems are exacerbated by expository laboratory experiments that are commonly used in organic teaching laboratories today, where students churn out products with little understanding of the chemistry involved (6–9). Instructional Laboratory Pedagogies In spite of a preponderance of literature that demonstrates the advantages of other laboratory pedagogies, expository experiments (also called verification labs, or traditional labs) still comprise the most common type of experiment (10). Students follow specific detailed directions to arrive at a predetermined outcome, the success of which is determined by how closely the students’ results mirror the known value. Expository experiments are often used to illustrate an important organic reaction or to verify a scientific principle or theory. The attractiveness of this type of experiment is one reason that expository experiments dominate the laboratory curriculum: the experiments are easy to set up, to supervise, and to grade (11). Exercises can be neatly fitted into available time blocks. Teaching assistants can be trained to monitor student progress and student questions are easily predictable. The instructor is generally in control as students produce the outcome of the experiment. Unfortunately, little meaningful conceptual learning occurs as a direct result of performing many of these experiments (2, 12) and students are generally not interested in doing these experiments because they can do the experiments without investing much thought (11). 848
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In contrast, open-inquiry experiments are those having no predetermined outcome. Students are expected to develop their own hypotheses and design their own procedures (13, 14). Such experiments enhance formal operational thought and critical thinking (5, 15). This is similar to the type of thinking expected of students who enter into laboratory research projects, in which much more planning and thinking are necessary than for doing expository experiments. However, instructors using this type of experiment may find organization to be a serious problem (16) and students may not have an adequate knowledge base to achieve a successful result (17). It is essential that instructors monitor student anxiety and assist in decision making, often through a process known as scaffolding (18). These experiments are student-designed and constrained by students’ knowledge and experience. Problem-based experiments also require experimental design by students. These experiments are often presented to students in terms of scenarios that require students to plan and carry out an experiment to solve the proposed problem. Problem-based experiments, which are deductive by design, are found frequently in upper-division undergraduate courses and in medical school laboratory settings. These experiments generate lots of interest and improve critical thinking skills, although they require extensive knowledge about the research topic by student participants and are very time intensive (19, 20). Involvement of the instructor in decision-making is important for the success of these experiments. Problem-based experiments, like open-inquiry experiments, have an experimental design created by students within the boundaries of their knowledge and experience. Guided-inquiry experiments combine the pedagogical advantages of open-inquiry methods with the practical advantages of expository experiments. Guided-inquiry experiments, also known as discovery-based experiments, usually provide students with a tested procedure to arrive at a predetermined, but unspecified outcome. As a result, students can be expected to gain higher cognitive achievement than from verification experiments (5, 6, 15). Unlike open-inquiry or problem-based experiments, guided-inquiry experiments can be readily adapted to large laboratory sections. In addition to inducing students to think more deeply, the guidedinquiry experiments often add an element of mystery for students. Exercising their critical thinking ability increases student interest in the activity. That is, students get to join in the hunt—just as in an open-inquiry experiment—yet without having to design the experiment. As with other laboratory pedagogies, there are also drawbacks to guided-inquiry experiments. The success of these experiments depends upon students’ obtaining good data and
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Textbox 1. Comparison of Laboratory Pedagogies (adapted from ref 16) Pedagogy
Experimental Design
Primary Learning Approach
Conclusion
Expository
Instructor-generated
Deductive
Predetermined
Open inquiry
Student-generated
Inductive
Undetermined
Problem-based
Student-generated
Deductive
Undetermined
Guided inquiry
Instructor-generated
Inductive
Predetermined
interpreting results correctly (21). The timing of experiments is often crucial. For guided-inquiry experiments to be most effective, students should perform the experiment well in advance of learning the concepts in lecture (22). In addition to the problem of timing of the experiments, other perceived disadvantages of guided-inquiry experiments are increased instructor time and possible student frustration (5, 21). Guidedinquiry labs are most successful when they focus on a single concept and provide opportunities for individual reflection and for class discussion (21). The four categories of experiments differ with respect to experimental design (whether the procedure is specified by the instructor or generated by the student), learning approach (whether inductive or deductive reasoning is required), and in the conclusion (whether one or multiple conclusions can be reached from the data). A summary of characteristics of the different types of experiments is presented in Table 1. A similar tabulation has been reported (16). Implementing Guided-Inquiry Experiments in the Lab Instructors have several options for incorporating guidedinquiry experiments into the laboratory curriculum. One method is to use published laboratory procedures from this Journal (22–31) or from a text containing discovery-based organic chemistry experiments (32, 33). A second method is to transform existing expository experiments to discoverybased experiments.
Literature Examples of Guided-Inquiry Experiments There are four primary categories of guided-inquiry experiments in the literature: 1. Inferring principles such as determining the pathway, mechanism, or stereoselectivity of a reaction 2. Solving an unknown 3. Solving the structure of an unanticipated product 4. Determining trends from multiple data collection
Inferring Principles Inferring principles after carrying out a reaction can be done by having instructor-generated procedures leading to a product, the identity of which will not be obvious. By applying principles addressed in the lecture class and by considering the physical, chemical, or spectral properties of the product, students can identify the product and rationalize the reaction pathway. Excellent examples of experiments in the inference of principles category are the study of selectivity in a reaction (34), the study of a reaction mechanism (25), and the study www.JCE.DivCHED.org
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of a rearrangement mechanism (29). Guided-inquiry experiments designed to focus on stereochemical analysis include using NMR spectroscopy to determine stereochemistry (23), determining the diastereoselectivity resulting from a Grignard synthesis (26), and evaluating the stereospecific reduction of benzil (33). By using spectroscopy and chromatographic techniques, students can deduce the mode of addition and predict relationships between products.
Solving for an Unknown A second type of guided-inquiry experiment involves identifying one or more unknowns. Qualitative organic analysis, most commonly included in the second-semester organic laboratory curriculum, is one example. Students can experience interesting and thought-provoking experiments using solubility tests, simple chemical tests, melting points of derivatives, and spectroscopic analysis. Asking students to predict structure and functionality from the physical property measurements and the outcome of each chemical reaction provides a better learning experience than merely matching student results with a table of unknowns (33). Some colleges have modified the traditional qualitative organic analysis scheme by having a greater spectroscopic emphasis (35). An experiment based upon both wet chemistry and spectroscopy can be included in the first-semester organic laboratory course, during which students identify an unknown alkyl halide, alkene, alkyne, or diene (33). Students study the reactivity of these functional groups and design a flow scheme to differentiate the functional groups based upon solubility, chemical reactivity, and spectroscopic methods. Other examples of experiments involving unknowns are combinatorial drug synthesis (36) and determination of the nature of products from nitration of unknowns (33, 37). An example of a similar experiment using a different reaction is that of an unknown starting material reacting by a known type of reaction, followed by isolation and identification of the product using spectroscopic analysis (40). Solving for an unknown need not be a rote activity, although if little thought is required of students to solve an unknown, it may become similar to a verification experiment (38). Identification of Unanticipated Products An extension of solving for an unknown is examining the structure of an unanticipated product of a reaction and then inferring the reaction mechanism. Examples from the recent literature include a mechanistic puzzle (30), a tandem aldol condensation with Michael addition (27), and an epoxidation of an alkene under two sets of reaction conditions leading to different products (39).
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In the Laboratory
Figure 1. Acetylation of phenanthrene.
Figure 2. Disproportionation reaction of 2-cyclohexenone.
Analysis of Trends
mechanistic argument to account for formation of the observed products (33). Another guided-inquiry experiment for aromatic substitution is the acetylation of phenanthrene (33). Even if students have prior exposure to the concepts of aromatic substitution, they will be unlikely to be able to predict the major reaction product. As shown in Figure 1, acetylation of phenanthrene can theoretically occur at one or more of five different positions on the three-ring system (33). Matching the possible products with standards using thin layer chromatography allows students to identify the main product of the reaction. Such an experiment also provides a good opportunity for discussions not only about techniques used and products formed, but also about the theory of electrophilic aromatic substitution and the applicability of resonance forms in predicting products. An even more challenging experiment is one involving an aldol condensation–Michael addition sequence in which students are asked to determine the structure of the product based upon NMR spectroscopic analysis (27). Based upon the structure of the product, students can propose a mechanism to explain its formation.
Determining trends from multiple data collection is an excellent path to guided inquiry, including examples such as these: • Collecting NMR shift values on representative functionalized molecules to generate a table of chemical shifts (31) • Investigating reactivity effects and directive effects on a series of substituted aromatic compounds towards bromination (33) • Determining characteristics of SN1 and SN2 reactions with respect to nucleophile, structure, leaving group, and solvent (33) • Determining the effect of structural features (such as molecular weight, chain length, branching, and functional group) on intermolecular forces and boiling point (23)
From Expository Labs to Guided-Inquiry Experiments A second method of incorporating guided inquiry learning into the organic chemistry laboratory curriculum is to modify an existing expository experiment. Often an expository experiment can be rewritten so that the outcome of the reaction is unknown to the student. This is particularly beneficial when the reaction can theoretically give several different products. Through identification of the product actually obtained, the student focuses on the mechanism of the reaction. Several examples of rewriting expository experiments to incorporate guided inquiry learning are discussed briefly here.
Aromatic Substitution Nitration of aromatic compounds, such as the synthesis of methyl 3-nitrobenzoate from methyl benzoate and sulfuric and nitric acids, is a typical second-semester organic experiment. In the expository experiment, students are given a step-by-step procedure, the structure of the product that will be obtained, and told how to match up properties of their obtained product with the spectral and physical characteristics of the meta-product. Rewriting and allowing students to determine the structure of the product through spectroscopic analysis (37) produces an element of guided inquiry. However, the experiment is still largely verification. To make this experiment a deeper learning experience, students might be asked to nitrate different aromatic compounds, post their identified products and use the combined class data to discern trends in the aromatic compounds that gave meta versus ortho- or para-substitution. Students may then postulate a 850
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Catalytic Transfer Hydrogenation Another example of transforming an expository experiment into a guided-inquiry experiment is catalytic transfer hydrogenation (41). Monosubstituted alkenes such as allylbenzene undergo catalytic transfer hydrogenation in excess cyclohexene at reflux in the presence of 10% Pd on C catalyst (33) or at room temperature in the presence of Pd on aluminum oxide catalyst (42). The expository version of this experiment provided the structures of the expected products. The experiment can be rephrased to give students the procedure for transfer hydrogenation of allylbenzene without telling them about the nature of the products (33). Following isolation and characterization of the products, students can deduce what has happened during the reaction and propose a mechanism to account for the aromatization of cyclohexene to benzene. A follow-up transfer hydrogenation experiment requires higher-order analytical skills: 2-cyclohexanone undergoes a disproportionation reaction, which is catalyzed by 10% Pd on charcoal. A redox reaction at the surface of the palladium catalyst causes oxidation of half of the 2-cyclo-hexenone to form phenol and reduction of the other half to form cyclohexanone (see Figure 2). Each of these compounds can be synthesized, separated, and purified and the structures worked out using NMR spectroscopy and GC–MS analysis. Students can then propose a pathway and a reaction mechanism based upon their characterization of the products (33).
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In the Laboratory
Conclusion Inclusion of guided-inquiry experiments in organic chemistry laboratory courses is desirable to improve conceptual understanding. The literature suggests (43a–d) that students tend to be more interested in and learn better from guidedinquiry experiments than from expository experiments. Several different types of guided-inquiry experiments have been categorized and discussed. This Journal contains numerous examples of guided-inquiry organic chemistry experiments that can be implemented easily in the undergraduate laboratory (22–31). Guided-inquiry experiments can also be created by modifying existing expository experiments to incorporate more unknown compounds and uncertainty on the student’s part about the outcome, thus generating greater interest in the experiment and what the experiment is intended to illustrate. Literature Cited 1. Boud, D.; Dunn, J.; Hegarty-Hazel, E. Teaching in Laboratories; Open University Press: Berkshire, UK, 1986; p 182. 2. Gallet, C. J. Chem. Educ. 1998, 75, 72–77. 3. Rubin, S. F. Evaluation and Meta-Analysis of Selected Research Related to the Laboratory Component of Beginning CollegeLevel Science Instruction. Ed. D. Dissertation, Temple University, Philadelphia, PA, 1996; p 95. 4. Hilosky, A.; Sutman, F.; Schmuckler, J. J. Chem. Educ. 1998, 75, 100–104. 5. Domin, D. S. J. Chem. Educ. 1999, 76, 109–111. 6. Pickering, M. J. Chem. Educ. 1988, 65, 143–144. 7. Crouch, R. D.; Holden, M. S. J. Chem. Educ. 2002, 79, 477– 478. 8. Schoffstall, A. M.; Gaddis, B. A. Discovery Experiments in Organic Chemistry. Abstracts of Papers, 223rd ACS National Meeting of the American Chemical Society, Orlando, FL, April 7–11, 2002; American Chemical Society: Washington, DC, 2002. 9. Gaddis, B. A. Conceptual Change in an Organic Chemistry Laboratory: A Comparison of Computer Simulations and Traditional Laboratory Experiments. Ph.D. Dissertation, University of Colorado–Denver, Denver, CO, 2001; p 351. 10. Abraham, M. R.; Cracolice, M. S.; Graves, A. P.; Aldamash, A. H.; Kihega, J. G.; Gill, J. G. P.; Varghese, V. J. Chem. Educ. 1997, 74, 591–594. 11. Montes, L. D.; Rockley, M. G. J. Chem. Educ. 2002, 79, 244– 247. 12. Gunstone, R. F.; Champagne, A. B. In The Student Laboratory and the Science Curriculum, E. Hegarty-Hazel, Ed.; Routledge: London, 1990; pp 159–182. 13. Green, W. J.; Elliott, C.; Cummins, R. H. J. Chem. Educ. 2004, 81, 239–241. 14. Senkbeil, E. G. J. Chem. Educ. 1999, 76, 80–81. 15. Tobin, K.; Tippins, D. J.; Gallard, A. J. Research on Instructional Strategies for Teaching Science. In Handbook of Research on Science Teaching and Learning, Gabel, D. L., Ed.; McMillan: New York, 1993. 16. Domin, D. S. J. Chem. Educ. 1999, 76, 543–547. 17. Hodson, D. Journal of Curriculum Studies 1996, 28, 115–135.
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