IR Cards: Inquiry-Based Introduction to Infrared Spectroscopy

In the Laboratory

IR Cards: Inquiry-Based Introduction to Infrared Spectroscopy Jacqueline Bennett* and Tabetha Forster Department of Chemistry and Biochemistry, SUNY College at Oneonta, Oneonta, New York 13820 *[email protected]

Infrared spectroscopy (IR) is common in the undergraduate chemistry curriculum because it is an effective, inexpensive, and rapid instrumental tool for identifying functional groups in organic samples. IR is often the first instrumental method discussed in organic courses because of its simple conceptual background. Many organic textbooks cover functional groups within the first several chapters, making IR an easy fit into early laboratories. Traditionally, students are introduced to IR in the following order: (i) wave theory and the electromagnetic spectrum, (ii) correlation table emphasizing numerical ranges of peak locations, and (iii) pictures of spectra to compare to the table for interpretation. One of the essential skills that students must develop to be proficient in IR interpretation is visual recognition of what an IR spectrum means. Unfortunately, even though students are frequently expected to analyze their experimental samples using IR, many students cannot interpret their spectra and must consult a correlation table every lab throughout a full-year course and still often have problems identifying their samples correctly. In our experience, students cannot translate the picture of the spectrum into meaningful information. Instead, they attempt to match every peak location to numbers in the correlation table, often ignoring the essential visual cues provided within the spectrum. In other words, they often miss the forest for the trees. We examined a number of common lecture textbooks to see how IR spectroscopy is presented. Even though IR interpretation is a visual process, most of the textbooks deemphasized the visual cues and instead focused on the peak locations by prominently displaying correlation tables early in the chapter. As shown in Table 1, few spectra are shown before correlation tables and only about half of the textbooks supply an adequate number of spectra for comparing similar functional groups (e.g., aldehydes and ketones). There does not appear to be any significant difference between IR coverage in full-year versus one-semester textbooks within the IR chapters, but outside of the IR chapters there is a significant difference. In the full-year textbooks, IR spectra are scattered throughout subsequent chapters, often as part of endof-chapter questions, whereas in the one-semester textbooks, coverage is restricted to the IR chapter. As one might expect, organic laboratory textbooks generally provide more examples of IR spectra. We examined three popular textbooks (Table 2) and found the same general trend of introducing a correlation table after just a few example spectra and then providing the bulk of the spectra later in the chapter. The two main differences between lecture and laboratory textbooks are that laboratory textbooks typically have a larger variety of functional groups represented and provide spectra of dispersants, which are absent in the lecture textbooks.

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Table 1. Presentation of IR Spectra and Correlation Tables in Organic Lecture Textbooks Spectra Total Number Preceding of Spectra IR the Correlation (Problem Chapter Table Spectraa)

Text Full-Year Solomons and Fryle (1)

2

0

McMurry (2)

12

4

5 (0) 6 (2)

Carey (3)

13

1

6 (1)

Wade (4)

12

0

36 (14)

Bruice (5)

12

3

22 (2)

Brown et al. (6)

12

1

13 (0)

Hornback (7)

13

10

24 (5)

Smith (8)

13

3

17 (5)

McMurry (biological) (9)

11

1

6 (0)

One-Semester McMurry and Simanek (10)

13

2

2 (0)

Brown and Poon (11)

11

1

16 (2)

Bruice (12)

15

1

12 (0)

a

Note: The problem spectra do not include the end-of-chapter problems.

Table 2. Presentation of IR Spectra and Correlation Tables in Organic Laboratory Textbooks

Text

IR Section

Spectra Preceding the Correlation Table

Total Number of Spectra (Problem Spectraa)

Williamson (13)

Chapter 12

0

16 (0)

Pavia et al. (14)

Part 6: Technique 25

6

25 (0)

Lehman (15)

Operation 36

2

15 (0)

a

The problem spectra do not include the end-of-chapter problems.

We describe an inquiry-based approach for interpreting IR spectra that is strongly grounded in the visual realm. Inquirybased and discovery-based instruction, as well as other inductive methods, has been shown to improve learning significantly in the sciences (16). Whereas the terms inquiry and discovery are often used interchangeably, an explanation of these and other inductive teaching techniques is provided by Prince and Felder (17). Inquiry-based instruction, in this article, is used to mean that students are not explicitly told how molecular structure

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r 2009 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 1 January 2010 10.1021/ed800009k Published on Web 12/18/2009

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Journal of Chemical Education

73

In the Laboratory

Figure 1. Example aldehyde IR cards: conjugated (benzaldehyde and cinnamaldehyde) and unconjugated (propionaldedhyde and valeraldehyde) compounds.

correlates with IR peak position and appearance. Instead, students deduce this relationship during the course of the described experiment. There are a number of inductive experiments previously described in this Journal, for example, regiochemistry of carvone epoxidation (18), student-designed procedures for electrophilic aromatic substitution (19), reconciliation of a “false assumption” with experimental data (20), and a discovery-based multistep synthesis (21). In all cases, “cookbook” approaches are minimized and students are not told the expected outcome. The inductive component of these experiments usually involves students deducing which product is synthesized by using tools such as spectroscopy, with which it is assumed students are already proficient. Inductive approaches to learning spectroscopy, in contrast, appear to be absent. Our technique is based on easily manipulated index cards, which we call “IR cards”, each containing an IR spectrum, a skeletal structure, and a chemical name (Figure 1). The approach is suitable for either a one-semester or a first semester of a fullyear course and familiarizes students with the important skills of problem-solving and pattern recognition, in addition to IR interpretation. Although students are provided with some basic guidance, they independently figure out the signature patterns of IR spectra within a functional group and later deduce how to distinguish between functional groups containing similar structural features. Manipulatives have been used successfully in organic laboratory; for example, Nelson created a two-page summary device to help students distinguish trends in electrophilic aromatic substitution (22) as well as a two-page device called the Nucleophile/Electrophile Reaction Guide to help students visualize reactions (23). We could find only one example of a manipulative for an instrumental technique, which was a general chemistry experiment for exposing students to 74


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Vol. 87 No. 1 January 2010

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fragmentation patterns in GC-MS (24). Because these students had no organic chemistry background, no real organic compounds were used. Rather, the “spectra” on these cards were created from “isomeric” words where word fragments were assigned mass values. Methods Preparation of the IR Cards All spectra were acquired on a Varian Scimitar 1000 Series FT-IR. Because our IR has an attenuated total reflectance (ATR) sample cell, we felt it necessary to acquire realistic IR spectra to use on these cards resembling spectra that students would later acquire for themselves. There are three significant differences between ATR spectra and non-ATR spectra accessible from free, online databases (25) or in textbooks (1-15): (i) high frequency peaks in ATR spectra are much weaker than in non-ATR spectra, (ii) carbon dioxide interference is more common in ATR spectra, and (iii) ATR spectra from solids are cleaner because no dispersant is necessary. Nine functional groups were included in this introductory experiment. Each noncarbonyl functional group was represented by three spectra. Each carbonyl-containing functional group was represented by four spectra (two conjugated and two unconjugated examples) to demonstrate the effect of conjugation on peak position. All IR cards included skeletal structures as well as chemical names and were printed on 58 index cards for easy manipulation. Execution of the Experiment Three classes participated in this experiment: the first semester of the full-year course (fall 2007), which primarily comprised chemistry and biology majors and other prehealth

pubs.acs.org/jchemeduc

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r 2009 American Chemical Society and Division of Chemical Education, Inc.

In the Laboratory Table 3. Student Survey Resultsa Fall 2007 (full year)

Fall 2007 (one semester)

Spring 2008 (one semester)

The IR cards made it easier to recognize functional groups in my own experimental IR spectra in later laboratories.

77

85

78

The IR spectra cards were easy to use and helped me identify characteristic peaks for each functional group represented.

79

71

78

The hands-on learning approach of the cards made it easier for me to recognize functional groups on IR spectra.

81

82

78

It was easy overall to identify similar IR characteristics for each type of functional group by comparing spectra from different compounds containing the same functional group.

74

56

70

I would have preferred to get a table of bond stretch types, stretching frequencies, and peak descriptions instead of the cards to learn IR interpretation.

30

35

37

The IR inquiry lab made me feel more confident in my ability to recognize functional groups from IR spectra.

53

56

59

Without the IR cards it would have been more difficult to understand IR spectra and functional group peaks.

74

82

67

Using IR cards was helpful for me to learn to recognize different functional groups from drawn structures.

72

62

78

Without IR cards I would have had a similar understanding of molecular structure and IR peaks of functional groups.

13

9

15

I would recommend future organic students use the IR cards to help learn to interpret IR spectra.

79

85

89

Checking out the IR cards would be useful to study for exam questions.

83

94

78

Figuring out for myself the relationship between functional group IR spectra appearance by seeing many different pictures of spectra and structures is more effective than getting a table of numbers (without pictures) to use.

62

47

48

Survey Items

a

The responses are indicated as percentages of students who agreed or strongly agreed with the statement.

students, and two different groups of a one-semester course (fall 2007 and spring 2008), which primarily comprised dietetics and biology majors. Each group of 2-3 students was provided with a deck of 31 IR cards that they first sorted into functional groups and then determined each functional group's signature pattern. A worksheet was provided to guide students and to help summarize their findings. Students then looked at the effect of conjugation as well as how to distinguish functional groups with similar structural characteristics (e.g., alcohols and carboxylic acids). In the fall 2007 courses, no IR background was provided beforehand. In the spring 2008 one-semester organic course, the traditional background approach was provided before students participated in this experiment. Assessment In all courses tested, student perceptions of the IR cards were surveyed. The IR worksheets that accompanied the IR cards were used to compare the classes that participated in this experiment. Instructor observations were also noted. Additional informal assessment data are included in the supporting information. Hazards There are no significant hazards in this experiment.


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Results and Discussion Student Perceptions Students evaluated the experiment favorably in several areas (Table 3). Students found the cards to be helpful for reinforcing their ability to classify organic compounds into functional groups both from their structures and from their spectra. All three courses rated each statement similarly except for the last statement, where both groups of the one-semester students found the process of figuring out IR patterns for themselves somewhat less effective than the full-year students did, which may be a function of the planned careers of these students. Students in the full-year course plan on careers with a high degree of problem solving and thus may have had a higher appreciation for this type of approach than the other students did. IR Worksheets The only means we have of a direct comparison among all three groups was the graded IR worksheet that accompanied the IR cards (Table 4). In the fall courses, when no IR background had been provided beforehand, students performed well and the performance between the two different level courses was consistent. In the spring course, when a more traditional approach was used, the performance was poorer overall. We saw that these students tended to rely on the numerical information from the


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In the Laboratory

to couple this experiment with a simple synthesis that yields several possible products distinguishable by IR, such as the alcohol oxidation puzzle by Pelter et al. (26), to further reinforce learning. Other innovative approaches, such as computational modeling (27) or online interpretation of practice IR spectra (28), could be combined with this experiment to make it a more effective learning experience. Because of the promising results, we are in the process of developing card systems for 13C and 1H NMR. This pattern-based system could be used for any technique that has a high pattern-recognition component.

Table 4. Worksheet Scores from the Classes

Term

Worksheet Treatment (Before or Percent After Traditional Scores Background) (av ( SEM)

Fall 2007 (first-semester of full-year course)

Before

87 ( 0.97

Fall 2007 (one-semester course)

Before

89 ( 0.90

Spring 2008 (one-semester course)

After

79 ( 2.0

correlation table provided as part of the background instead of using the visual cues within the spectra. Rather than evaluating peak characteristics, the students only considered peak locations and were not able to explain how to distinguish between functional groups. They simply supplied the numbers with little or no attempt at an explanation, showing a higher reliance on memorization of the correlation table numbers rather than the visual cues in the spectra. Instructor Observations One of the most striking differences between the fall and spring one-semester courses was students' ability to correctly determine functional groups when shown an IR spectrum in lecture. The fall-semester students could more often choose the correct functional group and were generally close to the correct answer when they chose an incorrect answer (e.g., ketone instead of aldehyde). Students in the spring semester, however, were generally very wrong when they chose an incorrect answer (e. g., alcohol instead of aldehyde). One example in particular that stands out is as follows: in a review session for the exam following the IR experiment, the instructor showed an IR spectrum of a terminal alkyne having a sharp peak of moderate intensity at about 3300 cm-1. Several students answered that this spectrum represented an alcohol. Their justification was “because alcohols have peaks at about 3300”. There was no consideration of peak shape. It was as if once the correlation table was presented, all other spectroscopic features became invisible. There were no errors of this magnitude in the fall semester. There was also less uncertainty in lab. Students were generally more capable of quickly deducing whether their reactions had succeeded and if their IR spectra “looked good” instead of asking the instructor these questions week after week. There was also less reliance on correlation tables, especially in the fall semester. Informally, the student author (T.F.) interviewed some of her peers with which she had organic chemistry during the 2006-2007 academic year. After describing the IR card experiment, these students said they would have preferred having a similar lab rather than the traditional approach that was used. They found learning functional groups and how to identify them using IR difficult and had not retained the information well. Conclusion We observed promising results after using the IR cards in lab. Students were more proficient in interpreting their IR spectra in later experiments if they did not see a correlation table before using the IR cards. We plan to expand our current selection of IR cards to include additional functional groups for use in an intermediate-level experiment. We also are planning 76


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Acknowledgment The authors are grateful to SUNY College at Oneonta for the purchase of the Varian Scimitar 1000 FT-IR equipped with ATR cell, Larry Armstrong for helping to test this experiment in his first-semester organic course during fall 2007 and for sharing ACS exam information, and the students from Chem 221 and 226 who participated during the 2007-2008 academic year. Literature Cited 1. Solomons, T. W. G.; Fryhle, C. B. Organic Chemistry, 8th ed.; J. Wiley & Sons: Hoboken, NJ, 2004. 2. McMurry, J. Organic Chemistry, 7th ed.; Thomson Brooks/Cole: Belmont, CA, 2008. 3. Carey, F. A. Organic Chemistry, 6th ed.; McGraw-Hill: Dubuque, IA, 2006. 4. Wade, L. G. Organic Chemistry, 6th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2006. 5. Bruice, P. Y. Organic Chemistry, 5th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2007. 6. Brown, W. H.; Foote, C. S.; Iverson, B. L. Organic Chemistry, 4th ed.; Thomson Brooks/Cole: Belmont, CA, 2005. 7. Hornback, J. M. Organic Chemistry, 2nd ed.; Thomson Brooks/ Cole: Pacific Grove, CA, 2006. 8. Smith, J. G. Organic Chemistry, 2nd ed.; McGraw-Hill: Boston, 2008. 9. McMurry, J. Organic Chemistry: A Biological Approach; Thomson Brooks/Cole: Belmont, CA, 2007. 10. McMurry, J.; Simanek, E. Fundamentals of Organic Chemistry, 6th ed.; Thomson-Brooks/Cole: Pacific Grove, CA, 2007. 11. Brown, W. H.; Poon, T. Introduction to Organic Chemistry, 3rd ed.; Wiley: Hoboken, NJ, 2005. 12. Bruice, P. Y. Essential Organic Chemistry; Pearson Prentice Hall: Upper Saddle River, NJ, 2006. 13. Williamson, K. L. Organic Experiments, 9th ed.; Houghton Mifflin: Boston, 2004. 14. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. Introduction to Organic Laboratory Techniques: A Small Scale Approach, 2nd ed.; Thomson Brooks/Cole: Belmont, CA, 2005. 15. Lehman, J. W. Microscale Operational Organic Chemistry: A ProblemSolving Approach to the Laboratory Course; Pearson Prentice Hall: Upper Saddle River, NJ, 2004. 16. Bransford, J. D.; Brown, A. L.; Cocking, R. R. How People Learn: Brain, Mind, Experience, and School. 2000. http://www.nap.edu/ html/howpeople1/ (accessed 4 Jun 2009). 17. Prince, M.; Felder, R. J. Coll. Sci. Teach. 2007, 36, 14–20. 18. Mak, K. K. W.; Lai, Y. M.; Siu, Y.-H. J. Chem. Educ. 2006, 83, 1058–1061. 19. Reeve, A. M. J. Chem. Educ. 2004, 81, 1497–1499. 20. Garner, C. M. J. Chem. Educ. 2005, 82, 1686–1688.


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In the Laboratory 21. Moroz, J. S.; Pellino, J. L.; Field, K. W. J. Chem. Educ. 2003, 80, 1319–1321. 22. Nelson, D. J. Chem. Educ. 2001, 6, 142–146. 23. Nelson, D. J. Proc. Okla. Acad. Sci. 2000, 80, 71–78. 24. Nowak-Thompson, B. Chem. Educator 2005, 10, 179–180. 25. (a) Sigma-Aldrich. Online Catalog. http://sigma-aldrich.com (accessed 4 June 2009). (b) SDBSWeb: Spectral Database for Organic Compounds. http://riodb01.ibase.aist.go.jp/sdbs/ (accessed 4 June 2009). 26. Pelter, M. W.; Macudzinski, R. M.; Passarelli, M. E. J. Chem. Educ. 2000, 77, 1481.


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27. Stokes-Huby, H.; Vitale, D. E. J. Chem. Educ. 2007, 84, 1486– 1487. 28. Merlic, C. A.; Fam, B. C.; Miller, M. M. J. Chem. Educ. 2001, 78, 118–120.

Supporting Information Available Student handout and worksheet; worksheet key; instructions for preparing IR cards; raw survey data for the three courses involved; additional assessment data; and copies of all 31 IR spectra used in this experiment. On request, the authors will send Keynote or PowerPoint slides of the IR cards. This material is available via the Internet at http://pubs.acs.org.


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IR Cards: Inquiry-Based Introduction to Infrared Spectroscopy

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