Two-Cycle Organic Chemistry An Alternative to Course Proliferation David E. Minter and Manfred G. Reinecke Texas Christian University, Fort Worth, TX 76129 The nast 25 vears have seen undergraduate organic chemistry d&elop into one of the most heavily populited courses on the tvnical universitv campus. With the advent of multidisciplin&y programs such i s neuroscience, medical technology, environmental science, etc., chemistry departments have been faced with the dilemma of providing courses to meet the needs, interests, and capacities of a variety of students. The net result has been a proliferation of specialized organic chemistry courses accompanied by corresponding increases in faculty teaching loads and support staff for laboratories. At one time, our department tried to keep pace with larger deoartments bv offerine a two-semester. nonmechanistic c o k e with ladoratory & organic chemistry and a one-semester oreanichiochemistrv course for nonmaiors in addition to thestandard two-semester sequence for chemistry majors and those ore-health professional students who reauired it (premedical and predental). However, i t soon became apparent that we could not justify maintaining such courses with existing faculty and limited lahoratory facilities. In response t o this problem and in anticipation that repetition of the volumin&s material and complicated co&epts of organic chemistrv would be beneficial icf., "spiral curriculum" ( I ) ] , the following actions were taken: ~~
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1) the non-mechanistic course sequence was cancelled, 2) the standard two-semester sequence was reorganized as a two-
cycle course,
3) organic lectures and laboratories were made separate courses
and given unique course numbers, and 4) each Laboratory was increased to a two credit-hourcourse con-
sisting of one hour of formal lecture and four hours of experimental work per week. This plan has now been in effect for nine years and has nroven remarkablv successful. Not onlv has i t nrovided scheduling flexibility for faculty and stud& while;educing the total number of courses, it has also resulted in students being exposed to more and learning more organic chemistry. The concept of the "two-cycle approach" (2) is not new, hut our version of the concept is; and we hope that the following description will guide others in their efforts to streamline the teaching of organic chemistry. The first semester lecture is taueht as an exoanded overview and follows standard texts desipeb for short courses. We have used the books by Holum (3).Moore and Barton (4),Brown (5),and Hart (6),and find these to be virtually interchangeable. Special emphasis is placed on bonding, structure, nomenclature, isomerism, resonance, and aromaticity by including information that is not in the text. All classes of organic compounds are discussed individually with particular regard for the electronic features and characteristic reactions of each functional erouo. However. mechanistic chemistrv is limited to hrief descriptions of the fundamental ionic reactions. We shunen the discussion of organic sbnthesis and omit spectroscopy entirely to allow more time f i r the study of bioloeical molecules. The associated laboratory course emphnsizes safety, basic techniques, and organic synthesis. In the first half of the semester, separation and purification procedures including fractional distillation, extraction, recrystallization, TLC, and
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VPC are taught. One additional experiment covering sodium fusion analvsis and s i m ~ l oreanic e oualitative functional mouo tests has been added;ecenky. ~ithe end of the fir; five weeks. a written examination and a laboratorv. practical are . given. The laboratory practical is rather time-consuming for the instructor hut serves better than any other method we have used to evaluate student progress a i d comprehension. In general, each person is given one of several mixtures to separate o; a sample of a contaminated organic compound to purify. On the basis of data accompanying each sample and perhaps one or two simple chemical tests, the student must determine the correct technique and perform the separation. The second half of the first semester lahoratory course is nrenarative oreanic chemistrv. Exoeriments are diverse and &rporate thz following re&tionAtypes:Diels-Alder, anhydride hydrolysis, dehydration, dichlorocarhene addition, Fischer esterification, Grignard, and electrophilic aromatic substitution. Again, the practical is used at the end of the term to evaluate experimental proficiency. Each student is given the starting material and a procedure for a preparation that has not been used during the semester. Grading is based on abilitv to follow instructions and set up as well as . glassware on prbduct yield and purity. The laboratorv lecture allows discussion of each experim e n t t h e o r y , mechanism, procedure, safety, and possible problem areas. In addition, we use some lecture time to introduce the theory of infrared spectroscopy and to discuss the use of chemical literature. Each student is required to do a literature search and submit a written, structured report on an individually assigned organic compound. This 1ectureAaboratory combination constitutes a detailed short course that satisfies minimum requirements for the medical technology BS and chemistry BA degrees. Environmental science and nutritipn majors need take only the first semester lecture. Of those who continue the sequence, the majority are pursuing BS degrees in chemistry, biology, or neuroscience or are in the premedical or predental programs. The second semester lecture is a mechanistically oriented course for which we have used the texts by Morrison and Boyd (7),Streitwieser and Heathcock (81,Wingrove and Caret (9), and Solomons (10).The material is much more physical than descriptive and is taught on the assumption that students are familiar with all aspects of bonding, structure, nomenclature, elementary reactions, and principles. In one sense, the course is a review-of the first semester, but the level of sophistication is much higher. Emphasis is placed on thermodynamics, kinetics, transition state theory, reaction mechanisms, and multi-step organic synthesis. We have used two conceptually different methods for presenting the material. The classical approach follows the general outlines of the texts listed above. However. certain chapters are purely review and can be omitted entirely. Others can he shortened sienificantlv " " hv " disreeardine the first few sections on structural features, nomenclature, etc. Surprisingly, this approach allows us to cover a larger amount of material in one semester than we were able to cover in two semesters before the course was reorganized.
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Volume 62 Number 1 January 1985
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The "non-classical ao~roach."as defined in the oreface to "Organic Chemistry" hy~endrickson,Cram, and ~ a m m o n d ( l l ) , organizes reactions into broad classes by mechanistic type rather than by functional group. We have used a modification of this method with Wingrove and Caret (9),and Solomons (10) by treating these books as references instead of texts. Students are expected to use the table of contents to locate pertinent information when specific reading assignments are not given. The course is divided into eight maior topics primarZy by reaction type: free radical ;eactiois, electrophilic addition, nucleophilic addition, elimination, substitution at sp' carbon, substitution at sp2carbon, pericyclic reactions, and organic synthesis. The extent to which each tooic is subdivided is flexible. and subiecLs not addressed in the tkxt are easily included. For exampie, under the major topic of elimination reactions, we discuss E l , E2, E l c ~and , concerted eliminations (chromate ester decomposition, Cope elimination. acetate and xanthate ~vrolvsis.decarboxvlation. etc.). The "non-classical approach is probably bet& than the classical one for increasingthe students' predictive powers. Since discussions of mechanism are not limited to one functional group, students learn to recognize the similarities hetween elec&onically analogous stru&res even if they have not seen a specific case. Also, this teaching method allows a more definitive identification of particularly gifted individuals who tend to excell at learning by association. Although average students seem to learn just & Auch regardless of meihod, thiy are more secure when information is presented in the order of appearance in the text. The only disadvantage of the "non-classical approach" we have noted is that examination scores are sometimes widely scattered and difficult to evaluate. The second semester laboratory is a course in spectroscopy and organic qualitative analysis. At least 40% of the total lecture time is soent on the theow and oractical aoolications of 'H NMR an2 infrared spect;osco&. An additional two lectures cover briefly I3C NMR, ultraviolet spectroscopy, and mass spectrometry. The remaining time is used for discussing classification tests and svnthesis of derivatives. We use Shriner et al. (12) as the text and a supplementary spectroscopy workbook. Experimental work consists of identifying five singlecomponent unknowns by using chemical tests, physical constants, derivative melting points, and spectral features. Students are responsible for obtaining their own IR spectra of the unknowns. In addition, students are provided with 'H NMR spectra of any two samples they choose. Since we do not limit the selection of unknowns to those listed in the derivative tables of the text, students often find it necessary to utilize their knowledw of the chemical literature from the first semester laboratory course. One of the most useful tools we have found for teaching the systematic approach t o compound identification is an interactive comouter nroeram written on-camvus (13). . It eives us an early opportinit; to evaluate and correct if necessary the student's ability to interpret results and follow a logical sequence. The use of computer unknowns has resulted in a noticeable increase in laboratory efficiency and now allows us to conduct the course as a self-paced activity. Taken in its entirety, the coursework described above constitutes as rigorous a treatment of undergraduate organic chemistry as any we have seen. Taken individually, the first semester^ lecture and laboratory are discrete and self-contained; and it is precisely this organization that gives such enormous flexibility to the program. The advantages are numerous and have been summarized below:
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need 1. The ~-~ in oreanic ehemistrv -~ ..-for a seoarnte short course , is ~
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eliminated sinre the first lecture course rovers all functional groups and the aawriated laborntory tearhes all the bask techniques in a single semester. This frees organic faculty to teach special topies and help in other areas. 78
Journal of Chemical Education
2. It is easier to standardize each course. AU second-semester students have the same background regardleas of who teachea the fmt semester of lecture. 3. Becaw lectures and laboratorieshave differentmume numbers, they may he taken independently. Students such a8 our own environmental science and nutrition majors, who need only the first lecture course, are not forced unnecessarily into the laboratory. Overall, this decreases the total enrollment in laboratories. 4. Premedical students in the three-year curriculum who take the MCAT early in the spring of their sophomore year have already completed our annotated survey course. This is amueh better preparation for the MCAT than the first half of a standard two-semester sequence. The same advantage applies to premedical students in four-yearprograms who defer taking organic chemistry until the junior year. 5. Students like the organization of the course. Classroom surveys indicate that the overview followed by a sophisticated review is popular, and students helieve that they learn and retain more information.
The major disadvantage of our program is that transfer students who have already completed one semester of organic chemistry elsewhere do not have the appropriate background to continue the sequence a t Texas Christian University. Conversely, our students have a similar problem when they transfer to other universities. The use of different texts for each lecture and lab course adds to the total cost of textbooks but may have the advantage that students read some of the same material presented from two points of view. The real worth of our two-cycle hpproach, however, is that students are exposed to more, learn more, and retain more organic chemistry. American Chemical Society standardized final examinations, given periodically during the past 12 to 14 years, serve to substantiate that claim. The ACS examination designed for brief courses has been used often a t the end of the first semester. Invariably, the class median has ranked in the 80-95 vercentile ranee on the national norms. Such high scores are'to be expectd, however, since our first semester lecture is much more intensive than a standard short course; and the students, most of whom are science majors, are not restricted to those who normallv take survev courses. The most meaningful data are the scor& on the A& examinations for "long" organic chemistry given at the end of the second semester. As shown below, the first entry (1973-74) typifies class performances before introduction of the twocycle approach. Since 1974, when the course was reorganized, our students have ranked in the top 30% of the nation on the average. Scores on the ACS Examination for "Long" Organic Chemistry Given at the End of the Second Semester Academic Year
National ACS Percentile of the Class Median
1973-74 1974-75 1975-76
65
roan-a?
70
48 85
In conclusion, the use of a two-cycle course structure for undergraduate organic chemistry has increased both the efficiency with which our department can handle its teaching responsibilities and the quality of the instruction. We are convinced that the simplicity, flexibility, and efficacy of this methodology make i t one of the best ways to avoid the problems associated with creating new courses. Literature Clted (1) Brunar, J. S.,"ThePmceaofEducation," Harvard University P w ,Cambridge, MA, 1918,pp.13.52-54. (2) Gutaehe, C.V..andPasto, O.J.,"Fundamon+Aaof Organic Chemis~y,"Pmntiee.HaU Imc., E n & d Cliff%NJ,1975. (3) Holurn. J. R.,"OrganicChemis~y:A BriefCouns:'John WdeyandSans,NewYork, 1915.
(4) Mmm, J . A,, and Barton, T. J., "Organic Chemistry: An Overivem." W. B. Saundcra
Company. Phiisdeiphis. 1978. (5) B r m . W. H.. "lntmduction to OlgsnicChemistry." 2nd and 3rd ed., Willard Grant P-. Boston, 1978,snd 1982. (6) Hart, H.. '"Organic Chemistry: AShort murae."6thed., Houghton MifflinCompsny, Boston, 1983. (7) Morrison,R.T.. andBoyd, R N., 'WmanieChemiatry"3rd ed..AUynand Bamn,Inc.,
New York. 1981. (10) Soiomons, T. W. G.."OrganieChemistry." Znded., John Wiley and Sons,N w York, 1980. (11) Hendrickmn, J. B., Cram, D. J., and Hammand, G. S.. "Organic Chsmisry," 3rd ed., McGraw-Hill Bmk Company. New York, 1970. dnta(12) Shriner,R. L..Fwan. R. C., Curtin, D.Y.,-iM ficationof Ormnie Com~oundd'Othed.,John Wilevand Son.. NearYork. 1980.
Volume 62
Number 1 January 1985
79
