Robert George Landolt Muskingum College New Concord, Ohio 43762
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A o n e - M O N ~Course ~ in instrumental Organic structural Analysis
During our first January "Winterim," we offered a problem-oriented course in qualitative organic analysis based entirely on instrumental determination of structure.' The class was composed of eleven junior and senior chemistry majors, each of whom was asked to identify a series of four "unknowns." Techniques available to the students included proton magnetic resonance, infrared, and ultraviolet-visible spectroscopy. Course Structure
One advantage of an "interim" semester is concentration on one subject; of equal importance, however, is the flexibility afforded an instructor in designing his course. In the present case, a modified lecture-discussion approach was utilized. At the beginning of each of four weeks, reading assignments, workbook problems,%and the week's unknown were assigned. One to two hours of lecture were held on Mondays and Tuesdays, followed by a question-and-answer period the next day. Discussions were sometimes carried into Thursdays, but generally the group met together on the last two days of the week to discuss results of each individual's investigation of his own problem. Each student was expected to characterize fully all of his unknowns. Beyond this, there were no quizzes or final This approach is not unique with Muskingum. I n late 1967, after I had laid plrtns for this course, I learned of a similar course being offered a t Austin College, Sherman, Texas. At this time I worlld like to acknowledge the helpful conversations held with Dr. W. B. Guerrant, then a t that institution. Mnskingum College operates under s. modified 14:4: 14 weekratio semester plan. Each student may elect to take one course during the month-long January term for hourly credit, and
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Molecular formulas were supplied with the first set. The number of protons, molecular weight, and elements present were given with the second set, and the molecular weight plus the elements present were provided with the last sets. As a last resort, n. student in difficulty was provided with the percent carbon and hydrogen for his last unknown. Our sincere appreciation is given to the following companies for supplying developmental compounds a t no charge: Velsicol Chemical Corporation, Luhrizol Corporation, General Aniline and Film Corporation, Crown Zellerbach, Calumbian Carbon Company, Ethyl Corporation, Michigan Chemical Corporation, Ott Chemical Company, Maumee Chemical Company, and Petro-Tex Chemical Corporation. VARIANASSOCIATES, "High Resolution NMR Spectra Catalogne," Val. 1, 1962; Vol. 2, 1963. 6 NATIONAL RESEARCH COUNCILAND NATIONAL BUREAUOF STANDARDS, U. S. Government, "Infrared Spectral Data Cards.'' This collection of over 2500 infrared spectra is indexed by molecular iarmula and is also sortable according to absorption bands.
exam as such. The instruments were available to students throughout the week. Students receive a brief introduction to infrared spectroscopy in their first semester of organic chemistry, the prerequisite for this course. No further lecture time was spent in this area. I n fact, none of the techniques was subject to rigorous lecture treatment. Nuclear magnetic resonance, ultraviolet spectroscopy and, to a lesser extent, mass spectrometry, were introduced with illustrations, and various available reference resources were discussed. As was intended, a considerable number of questions were raised by students, and the discussions that arose from them provided the balance of instruction. Choice of "Unknowns"
The choice of unknowns was the most difficult but most intriguing part of course preparation. In the relatively small class, an attempt was made to match student to unknown for each of the four sets, avoiding duplication of functionality, etc., and assigning compounds to parallel student interests and capability. All compounds in the first set were relatively uncomplicated and were picked to illustrate simple nmr chemical shift concepts and to review identification of functional groups by infrared. Each succeeding set of compounds had more complicated structures, and less information was provided as to elemental compo~ition.~ Common stockroom compounds sufficed for the simpler unknowns; more complicated ones were selected from research program stocks and from industrial source^.^ The latter were picked for two reasons: general safety and handling information were available from chemical companies, and students were more or less intrigued with working with non-trivial developmental materials. Modus Opemndi
Because each student was confronted with his own problem, considerable individual initiative was required from the beginning, and most of the students responded well. I n addition to using tabular data in references, most learned early the value of such compilations of spectra as the "Varian catalog^"^ and the "Infrared Spectral Data Cards Colle~tion."~As unknowns became complicated the literature was used more thoroughly, and the complementary value of various techniques grew more apparent. The practice of seeking good model compounds was encouraged. Though mass spectrometry hardware was unavailable, concepts were introduced, and students made good use of the "nitrogen rule," the method of determination of molecular formulas from elemental tables, and the use Volume 46, Number 10, October 1969
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of molecular formula in determining the number of "unsaturation sites."' Results and Comments on Student Response
Of forty-four unlcnowns issued, thirty-seven were completely identified. A few errors resulted from inability to distinguish between positional isomers of aromatic compounds or between possible configurations of double bonds; in others missed, significant progress was made t,oward identification of functionality, but pieces were not put together properly. Student response to the course was exceptional. This probably is attributable to several factors including: the possibility for concentrated work afforded by thc interim program; the lack of "quizzes" which reduced the tendency to memorize; and the problemoriented nature of lab work. The fact that each iudividual had his own problems both encouraged independence and provided incentive for class participation. One never knew when an approach used by a classmate on a differentproblem might apply to his own situation.
' SILVERSTEIN, R. M., A N D BASSLER, G. C., "Spectrometric Identification of Organic Compounds," John Wiley & Sans, Inc., . New York, 1967, C h a ~ 1.
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Journal o f Chemicol Educofion
From the viewpoint of the instructor, in addition to the flexibility of the interim system mentioned earlier, this course was an especially enjoyable one because the problems were not cut and dried. Often unexpected situations arose involving stubborn solubilities, overlapping absorptions, or difficulties in finding model compounds which developed into good learning situations. Qualitative analysis by instrumental techniques is a particularly useful teaching method because it brings home in a forceful manner the realities of molecular architecture we call structure. Students readily appreciate the unique character of benzene derivatives as shown by down-field shifts of aromatic protons in nmr spectra. Bathochromic shifts observed with a,p-unsaturated chromophores show clearly the ramifications of conjugation. Nuances of structure can be demonstrated with considerable impact when one is faced with the problem of proceeding from spectral evidence to reasonable structures. The three nnsplit nmr methyl absorptions of a compound later identified as camphor, for instance, effectively illustrated the locked conformer effect of the cage structure. Thus, spontaneity of learning by encounter experienced by students in classical qualitative analysis was carried over into the realm of modern instrumental analysis.
