Activity pubs.acs.org/jchemeduc
A Jigsaw Classroom Activity for Learning IR Analysis in Organic Chemistry T. Nicholas Jones,* Kate J. Graham, and Chris P. Schaller Department of Chemistry, College of Saint Benedict and Saint John’s University, St. Joseph, Minnesota 56374, United States S Supporting Information *
ABSTRACT: A modified jigsaw classroom activity is presented for the integrated study of functional groups and their characteristic infrared absorption frequencies. Students individually performed semiempirical studies on the vibrational frequencies of an assigned molecule and compared the results to an experimental spectrum from a database. The results of these studies were discussed in a small group exercise to discover the spectral features that are most useful in identifying particular functional groups and their relationship to structures.
KEYWORDS: Second-Year Undergraduate, Organic Chemistry, Collaborative/Cooperative Learning, IR Spectroscopy, Molecular Modeling
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of a large topic yet still demands individual responsibility throughout the process.
modified jigsaw activity was developed to introduce characteristic IR absorptions for a variety of different functional groups. The goal of the activity was to enable students to discover the relationship between IR spectroscopy and functional groups. To accomplish this goal, groups of 4−6 students compared experimental IR spectra with theoretical vibrational calculations to discover characteristic absorption frequencies and associated bond vibrations for a set of related molecules. These groups then shared their conclusions with the class to produce a comprehensive view of spectroscopy relationships. This activity was used in the fall semester of a two-semester introductory organic chemistry sequence at a small, liberal arts college; there were about 30 students in a lecture section. Despite many apparent advantages, group work in the classroom can present some difficulties.1−6 Most notable is the problem of disparate levels of ability and motivation among group members, as a result of which one good student dominatesand learnswhile the others watch or a weak student is supported by everyone else’s work. Group work can also be frustrating if the same approach is overused, as these methods depend in large part on student motivation that can be diminished if activities become mundane. Thus, it can be important to employ a range of approaches in the classroom. Although they have not received much attention, jigsaw7 classroom activities8−10 in which students work on “puzzle pieces” of a larger topic are an effective way to lead students to construct concepts while encouraging full group participation. This approach is particularly attractive in dealing with the unmotivated student because it focuses on group understanding © 2012 American Chemical Society and Division of Chemical Education, Inc.
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ACTIVITY DESCRIPTION Students were assigned a textbook reading on functional groups and a computational modeling assignment. The modeling assignment required them to perform a semiempirical calculation to determine the vibrational frequencies of their assigned compound.11 Rapid geometry optimization and frequency calculations were performed using the AM1 method of Spartan. It is important to note that the AM1 method overestimates frequencies by about 10%.12,13 Upon completion of the calculation, students visualized the molecular vibrations corresponding to the calculated frequencies and compared these data to an actual spectrum.14 In the computational experiment, students explored a variety of stretching and bending vibrations to be sure that they found frequencies characteristic of the functional group of interest. This is done to emphasize that IR spectroscopy is based on specific bond types absorbing radiation of discrete energies. The students were instructed to explore a variety of signals before preparing their data and analysis table. Students then prepared a table of six molecular stretches or bends for their compound. In this way, each student became an “expert” on the IR spectrum of one compound. At the beginning of class, students handed in a copy of their IR Spartan assignment for grading15 and met in small groups wherein the compounds studied were similar (e.g., carbonyl Published: July 25, 2012 1293
dx.doi.org/10.1021/ed200334n | J. Chem. Educ. 2012, 89, 1293−1294
Journal of Chemical Education
Activity
learn and retain information better when active constructivist approaches are used.20−24
compounds, hydrocarbons, etc.) but differed in key ways. The groups were instructed to find the similarities and differences between their spectra (i.e., what key absorbances distinguish these functional groups?). Unlike traditional Jigsaw activities, this one does not include an “expert group” meeting. This choice in conjunction with the Spartan assignment grading prevents students from blending in and supports individual accountability. Toward the end of the class period, groups were asked to develop a short presentation on their related compounds for the entire class. Drawing from these informal presentations, a compiled table of characteristic absorbances was developed on the blackboard by the instructor. Although there are a variety of introductory IR spectroscopy activities for both class and laboratory settings,13,16 this one is unique in that individual student computational experiments are coupled with jigsaw-based group and whole-class presentations.
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ASSOCIATED CONTENT
* Supporting Information S
Notes to instructors, student handouts, sample data tables, grading rubric, assigned compounds. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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RESULTS The most striking feature of this exercise was the way it allowed coverage of multiple concepts in one class: all of IR interpretation as well as a brief introduction to functional groups. These concepts were subsequently further developed in a homework assignment entailing more detailed functional group nomenclature and in laboratory experiments17 requiring IR analysis to help determine the structures of unknowns. Students were graded on their individual computational assignment that was unique from all the other students’ assignments, thereby enforcing individual responsibility. As a result, preparation before class was generally good and led to all students participating in the group activity. The students have easily found the correlation between the physical vibration that they viewed and the frequency for the same bond stretch or bend reported in a table. Difficulties in this area are typically associated with students skipping a step in the directions such as not making the 10% correction or failing to look at an IR table. Typical student responses to discussion questions indicated that this activity allowed them to develop a sense of when IR spectroscopy would be most useful as well as its limitations. Many students responded that they could narrow a list of given compounds to those with similar functional groups, but not necessarily be able to identify exact compounds without a reference spectrum. Nearly all students recognized that IR spectroscopy could be useful for validating an expected product. Most students noted that IR analysis of purity would work best if the contaminant contained functional groups that did not overlap with those of the compound of interest.
REFERENCES
(1) Bodner, G. M. J. Chem. Educ. 1986, 63, 873−877. (2) Dinan, F. J.; Frydrychowski, V. A. J. Chem. Educ. 1995, 72, 429− 431. (3) Harvey, L. C.; Hodges, L. C Chem. Educator 1999, 4, 89−93. (4) Browne, L. M.; Blackburn, E. V. J. Chem. Educ. 1999, 76, 1104− 1107. (5) Paulson, D. R. J. Chem. Educ. 1999, 76, 1136−1140. (6) Spencer, J. N. J. Chem. Educ. 2006, 83, 528−533. (7) For a brief history and discussion of the jigsaw approach see http://www.jigsaw.org. (accessed Jul 2012). (8) Seetjaraman, M.; Musier-Forsyth, K. J. Chem. Educ. 2003, 80, 1404−1407. (9) Whitlock, C. R. Chem. Educator 2009, 14, 96−97. (10) Davis-McGibony, C. M. J. Chem. Educ. 2010, 87, 409−411. (11) See Supporting Informations for IR Frequency Calculation Assignment. (12) Although we have chosen to use uncorrected AM1 frequencies for our activity, it is possible to obtain better agreement between calculated and observed frequencies using scaled HF/3-21G* results.13 (13) Stokes-Huby, H.; Vitale, D. E. J. Chem. Educ. 2007, 84, 1486− 1487. (14) Students were able to retrieve authentic vibrational spectra from Sigma-Aldrich (http://sigmaaldrich.com) or Structural Database for Organic Compounds SDBS (http://riodb01.ibase.aist.go.jp/sdbs/cgibin/cre_index.cgi?lang=eng). (accessed Jul 2012). (15) See Supporting Informations for the IR Spartan assignment grading rubric. (16) Bennett, J.; Forster, T. J. Chem. Educ. 2010, 87, 73−77. (17) Graham, K. G.; Johnson, B. J.; Jones, T. N.; McIntee, E. J.; Schaller, C. P. J. Chem. Educ. 2008, 85, 1644−1645. (18) Milner-Bolotin, M. The Effects of Topic Choice in ProjectBased Instruction on Undergraduate Physical Science Students’ Interest, Ownership, And Motivation. Ph.D. Thesis, The University of Texas at Austin, 2001. (19) Wood, C. M. J. Marketing Educ. 2003, 25, 240−249. (20) Yager, R. E. Sci. Teach. 2000, 67, 44−45. (21) Gutwill-Wise, J. P. J. Chem. Educ. 2001, 78, 684−690. (22) Fink, L. D. Creating Significant Learning Experiences: An Integrated Approach to Designing College Courses. Jossey-Bass Publishers: San Francisco, CA, 2003. (23) Ram, P. J. Chem. Educ. 1999, 76, 1122−1126. (24) Hmelo-Silver, C. E. Educ. Psych. Rev. 2004, 16, 235−266.
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CONCLUSIONS Implementing a variety of active classroom activities can be a useful approach to encourage active learning and still demand individual responsibility in the organic chemistry classroom. Although the preparatory activities are somewhat timeintensive, a large topic can be covered in one class period. We have observed that our students rapidly developed an understanding of the utility of IR spectroscopy and its limitations. This observation ties with the knowledge that they will be responsible for material as the expert on a “puzzle piece”; they tend to do the assigned project or homework more carefully.18,19 The modified Jigsaw approach eliminated the “expert group” meeting, thus, reinforcing individual accountability. This approach builds on recent findings that students 1294
dx.doi.org/10.1021/ed200334n | J. Chem. Educ. 2012, 89, 1293−1294
