The Role of Surprise in the Organic Laboratory Jeffrey E. Keiser Coe College, Cedar Rapids, IA 52402 Teachers of organic lahoratory must contend with many aspects of human psychology. One of these is the problem of expected results. A common example of this situation is students' expecting "the answer" (some sort of perfect result) and being unsatisfied with their own data as the best available result. I t is true that many experiments of necessity must have an expected, normal, or even perfect result that students are expected to achieve. This necessity, however, can contribute to the problem of students' approaching their lahoratory work in an unthinking way, following a recipe that they expect will give them a particular result without thinking about either the process or the result. I t is the view of this teacher that this psychological problem can e offset a t least in part, by assigning experiments that givjthe stuj dents unexpected results. Some of my favorite examples follow. Fractional Distillailon Fractional distillation procedures are common in organic lahoratory courses. Assigning a mixture of toluene and methanol together with gas chromatographic analysis of the distillation fractions illustrates the surprise principle very nicely. Students expect the first fraction to he nearly pure methanol and the third to be nearly pure toluene. A recent class averaged 72 wt % methanol for fraction 1and 97 w t % toluene for fraction 3. The volume of fraction 1averaged 16 mL, fraction 3 averaged 4 mL. (The students started with 24 mL of a50-50vlvmixture.) These datacaused some consternation among the students, and I let them ponder the matter for a few days before leading a discussion of the results. Before very long, students were suggesting azeotrope formation as an explanation for these data. The reported (I)value for the methanol-toluene azeotrope is 72 wt % methanol.
health advantages (3). Dichromate procedures offers some educational advantages, however, and are included in some contemporary textbooks (4). Dichromate procedures nicely illustrate the surprise concept. Student cyclohexanone samples prepared according to textbook dichromate procedures often contain 20-30% starting material by gas chromatography. Students tend to expect their products to he nearly 100%pure. The actual and surprising result of impure products can lead to interesting class discussions of the impact of variables on purity and can also lead students to conduct experiments testing possible improvements to the procedure. Chlorlnatlon of 2,4-Dimethylpentane This surprise, first reported in 1966 (51, has been suggested to me by a colleague (6). The chlorination of 2,4& methylpentane (isoocatane) can produce the three isomeric monochlorderivatives (71,
Reduction of Ketones
The process of reducing an aldehyde or ketone t o its parent alcohol is common in many organic lahoratory textbooks. The sodium horohydride reduction of camphor as described in a now out-of-print textbook (2) is a nice example. (Providing a textbook citation conveys a ring of authority and authenticity that enhances the later surprise.) I like to assign the procedure as described in the book and require an infrared spectrum of the crude product, stressing the expected result of disappearance of the carbonyl hand and awearance of OH absorbance. The student spectra. howeve;;contain quite an intense carhonyl hand, p;esumably due to contamination of the expected product with starting material. Some students notice thiscarbonyl absorbance, are surprised, and think ahout their experimental results, sometimes reaching the correct conclusion. Some others just hand in the spectrum without noticing the unexpected peak and are chagrined when their oversight is pointed out to them. All are stimulated to examine their experimental results critically. Oxidation of Cyclohexanol Commercial blearh may be replaring dichromate as an oxidizing arent for secondary alcohol^ in the organic lahoratory becaus&the former offe~seconomic,environmental, and 78
Journal of Chemical Education
corresponding to the abstraction of primary, secondary, and tertiary hydrogens, respectively. Students expect a concentration of isomer 3 greater than the statistical share of hydrogens leading to it since they are aquainted with the free radical reactivity sequence for hydrogens of 3O > 2O > lo. What they find, however, is that these particular hydrogens have abnormally low reactivity. This low reactivity has been explained (5,8,9) in terms of conformational effects which shield these 3" hydrogens from attack by free radicals. I am firmly convinced that surprises can often shake students out of an unthinking approach to their laboratory work, and I recommend both the concept and the above examples to other organic laboratory teachers. Literature Cited
3.
Mohrig.J.R.:Nienhuls,D.M.;Linck,C.F.;VanZoren,C.:For,B.G.:Mahaffy.P.G.J. Chem. Educ. 1985.62.519-521 and references therein.
4. A u k A. Techniques and Experimentsfor Organic Chsmhfry, 5th ed.; Allyn & Bacon:
Boston, 1987; p 366. Durat, H.D.;Gokel, G.W. Experimenfol Ormnie Chemulry. 2nd ed.: Mffimu-Hill: New York, 1987: pp 3%-391. 5. Rusnell,G.A.:Hamey.P.G. J.01p. Cham. 1966.31, 1369.1871. 6. Auk. A , Cornell College, personal mrnrnunication, 1936.
7. Ault, A. Techniques and Ezpwimentsfor Orsonic Chemwtry, 5th ed.: Allyn & Bacon: Boston, 1987,pp 1&141. 8. Bmok, J. H. T. Trons. Forodoy Soc. 1957.53.327-332, 9. Bridger,R.F.;Russell,G.A. J, Am. Chrm. Soc. 1963,85. 3754-3765.
Volume 65
Number 1
January 1988
79
