A Problem-Solving Approach To Teaching Organic Laboratory James H. Cooley University of Idaho. Moscow, ID 83843 A number of papers in this and related journals have called for a laboratory curriculum that provides a greater intellectual challenge to students (1-7). Unfortunately these papers have not provided a very good description of how to proceed with such a program. In 1987 we presented a few suggestions ( 8 ) ,and this paper describes my further effort in this direction for the sophomore oraanic laboratorv. In this laboratory c&e the emGhasis was placid on studenrs ohtaininpr and interpreting data. These ohiectives contrast with the &a1 objectives For the organic Ghoratory of making representative compounds and learning techniques. I t was our finding that, when students are provided with a description of the data that they are supposed to obtain, they do not take the matter of collecting their own dataat all seriously. When they are given an explanation of what the data mean, they accept such interpretations without question and complete the laboratory with minimal effort or ability t o interpret data. Also tbeir level of appreciation of the value of various techniques used to study organic chemistry is slight. Published laboratory manuals that give the results to be expected and their meaning do not force the students to think about tbeir experiments. Consequently a group of experiments has been written ( 9 ) to fit my objectives. Never do we (teaching assistants or I) say what the melting point or infrared spectrum will be, and we ask the student to draw what conclusions they can from the data. I have been satisfied rhat theie added objectives are compatible with the alreudy accepted ones, the learning of techniques, and the making of compounds. The student who bas poor technique does not get results to interpret. Further, students are required to make compounds in order to make observations on them. The additional goal was to bring students to the point where they could run reactions and discover what had happened from physical data, chemicaltests, and spectra that they had obtained by the end of the first semester. Of course i t can be argued that the structure of the product is as close as the lecture text. That is true, but for the beginning student there is a measure of uncertainty in finding an answer in another source. Thus the exercise is still a worthy learning experience. Furthermore, students obtain considerable satisfaction in that the data they obtain verify what is in the lecture textbook. Lecture texts usually describe only conclusions without providing the detailed evidence for them. Students accept this seeming dogma witbout question, but a laboratory that illustrates the way these conclusions are obtained can be supportive of the lecture.
The table gives a brief description of some of our activities. While the table lists the kinds of data and the expected interpretations, i t does not indicate my expectation that the interpretations be related to underlying theory. For example, the interpretation in the chromatography, recrystallization, and extraction experiments must relate to principles of solubility. The first experiment in which the student prepared and identified a product was the irradiation of rrons-1.2-dihenzoylethylene (12). A percent carbon and hydrogen for the product was provided so that students would see that the composition of the product was the same as that of the starting material. The effort to analyze the data and to solve the puzzle of what had happened seemed to be a gripping experience. After the data had been collected, we met as a class to discuss it. The meaning of each bit of evidencecolor change, mp's, change of R,'s, shift of the C=O stretch in the IR spectrum, and percent carbon and hydrogen-was considered. Finally, possihle structures of the product were suggested by students, and the merits of the proposed structures were debated. One student who was repeating the laboratorv and had done the experiment before with the w x t b o o k ~ r e s e n t a t i ~and n e x p ~ a ~ a r i ovolunteered n that after this careful analysis of each bit of data she u,as nuw able to understand the kxperiment. I was encouraged that the stress placed on interpretation of data to reach an answer was very important in increasing understanding by the students. Student comments in general were quite favorable on this process. Next in the sequence, 'H NMR spectroscopy was introduced. For several years we have found it possihle to teach interpretation of simple NMR spectra in one 3-h period to students who have had no previous introduction to the subject. To do this students are asked to predict the number of signals a variety of compounds have. Then they are asked to predict the chemical shifts, peak areas, and splitting patterns for a variety of structures. The majority have been able to solve 11 unknowns-methanol, acetic acid, toluene, pxylene, methyl ethyl sulfide, i-nitropropane, cumene, transdiphenylethylene, 1,1,2-trichloroethane, methyl ethyl ketone, and isopropyl iodide-in the remainder of the period. As homework students were then given an assignment of predicting the expected spectra of nine compounds: ethyl benzoate, ethyl benzene, n-propyl benzene, 4-chlorotoluene, 4-methoxybenzyl alcohol, 2-butanol, n-butyl acetate, butyrophenone, and tetrahydronaphthylene. In the second laboratory period one of these compounds was used as an un-
Volume 88 Number 8 June 1991
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Table 01 Currlculurn in the Order Used Experiment and # o f 341periods
Data to be Collected
Expected Deductions Change of R;s wilh increasino solvent .~oiaritv. . Chanoe n R, r with ncreasing compound polaraly Change 01 R.'r with reversal 01 polarq 01 stationary and mobile phases ( 10). Changes observed as a reaction progresses. Identification of components of analgesics ( 1 1).
min-Layer Chromatography 2 Periods
R,. size and
Physical Properties 1 Period
mp range. mixed mp range, bp range, relrectiva index.
ldentlficationof two unknowns, a solid and a liquid.
Infrared Spectra 1 Period
run IR spectra
Idemiflcation of five unknowns from a list of possible
Cryslaliization 1 Period
physical propsflies of pure and impure cry* lais
lnadiation of trancl.2dibenmyl ethyl. ene 1 Period
mp.
6.IR
Product was identified from data collected, and percent C and H that was provided ( 1 2 ) .
'H NMR 1 Pericd
Provided
data interpreted using number of signals, chemical shins. integration, and splitting.
'H NMR 1Period
1NMR spectrum determined
Working in groups of four. students identily four compounds from a list of 10 possibilities.
shape Of 8p01
unknowns. Expected solubility in hot and cold solvents. Change in propenies of purified sampies
Product identlfled from these data a6 acety fenocene ( 13).
Ferrocwne with Acetic Anhydride 2 Periods
even our very best students. Although the ability of students to interpret data properly was at first quite poor, they were very receptive to i n explanation and wire able to g a s p the essential concepts when a full explanation was offered. The final two preparative experiments in the first semester, the reaction of ferrocene with acetic anhydride (13) and the reaction of p-chlorobenzaldehyde with sodium hydroxide (14), were not especially challenging. The earlier, labored efforts a t interpretation of data were by this time replaced with adirect and confident approach, and the determination of these structures was handled with comparative ease and very well by the majority of students. At this stage of development this material has been used by a colleague who remains enthusiastic about it. His general comments are that the approach wasmore work both for him and the teaching assistant and that the students learned more. He also reports that student comments were very favorable and felt that the laboratory had been a worthwhile learning experience. The experiments chosen were good for building confidence in lahoratory work. Virtually all students obtained good data and were able to solve the problems posed. That the better student had the better understanding of processes and nrincinles was made clear in renorts and on examination; and grading was based on these. The teaching of the laboratory sections was carried out by several graduate teaching assistants, one American, one from Bangladesh, and anewly arrived Nepalese. All teaching assistants grasped the intent of this problem-solving approach without difficulty. From this experience the method does not appear to be difficult to implement with teaching assistants. In summary: Student attitude toward the laboratory remained positive. Student interest was directed toward understanding the process as much as getting the "right" answer. There seemed to be good understanding on the part of students of the logical methods available for studying organic reactions. Our effort to teach in this way was at times clumsy. I offer this description as a suggestion to those who believe that problem solving is a better way to present the organic labopatory. Our effort has been used with five sections, each having between 12 and 24 students of "run of the mill" sophomores meeting for 13 3-h periods during the first semester of their study of organic chemistry. An extension of the program for the second semester is under development and will continue with more complicated experiments concerned with structure determination, mechanism, and synthesis. ~
Extraction 1 Period
weight of benlaic acid
Bsnmc acld removea bom methy ene chlor de oy 5 O o Sodium bicarbonate but not by water.
pChiorobenza1dehyde with NaOH 2 Periods
2 products iso-
F T ~ ~ U sepamted CD by exbac tion and den! Iea oy R.. mp. R, hMR, and so ubil ty
lated. mp. IR. RI. NMR
Literature Cited
known,and students learned how to run the N M R spectrometer so as to get the needed data. Working- in groups - - of fonr, they identified four unknowns to turn in. During the development of this approach it was sobering to find that students could not give the textbook interpretation of observations such as the change in Rr with change in polarity of the developing solvent. Even an explanation of the depression of the melting point when two different substances are mixed was a formidable task. Equally awkward was to find that the majority of students failed to observe that the product spot waxed while the reactant spot waned the first time that thin-layer chromatography was used to follow the progress of a reaction. Clearly the approach, which a t times seemed trivial to me, held considerable difficulty for
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Journal of Chemical Education
1. Venkatschelsm,C.;Rudalph. R. W. J. Chem Edur. 1974.51.479. 2. Brantz, S.J . Chsm. Educ. 1985.62.899. 3. Hathaway.B. A. J . Chem. Educ. L987,M. 367. 4. Piekering M. Chron. Higher Educ. 1980.19 Web 19).80. 5. Abrahsm,M. P. J.Res.Sci. Teach. 19R2, IS, 155. 6 Pirkering M.d Chem. Edur. 1985.62.871 7. Pickerin8.M. J. Chem.Educ, 198R,65,143. 8. Cooley, J. H.: Evain.E.J.. Northwest RegionalMeetingof American ChemicalSrriefy, .Ilino
19R7 A h s t ~ ~ ~ l 1 1 1
.....,...., .... 13, (el Bnzak, R. E. J. Cham. Educ. 1966,43,73. (bl Williamson, K. L.Mocroscal~and Micrascais Oqanie Experiments; Heath: Lexington, MA. 1989: p 4W. 14. (a) Mayo,D.W.;Butchor,S.S.;Pike,R.M.J.Cham.Edur. 1985,62.149. (h1Mayo.D. W.: Pike. R. M.: Butcher. S. S. Microscol~01mnic Loborolary, 2nd ed.: W i k u
