In the Classroom
A Simple Assignment That Enhances Students’ Ability To Solve Organic Chemistry Synthesis Problems and Understand Mechanisms Jennifer Teixeira and R. W. Holman* Department of Chemistry, Idaho State University, Pocatello, ID 83209-8023; *
[email protected] Second-year-level organic chemistry students seem to uniformly struggle with solving multi-step synthesis problems. The inability to readily solve multi-step synthesis problems stems, in part, from the inherent design of the traditional organic chemistry course itself. The majority of second-year-level organic chemistry textbooks are organized by functional group (1–4). Faculty traditionally teach the material within these chapters with the central focus being reactions of the featured functional group. This teaching approach, while orderly and quite reasonable for systematically introducing properties and general principles, is not ideal for preparing students for the thought process involved in solving organic synthesis problems (5). The textbooks present the reactions in a forward sense, namely, A + B → C, where A is the featured functional group. The retrosynthetic approach (involving the synthesis of a target compound) mandates that the students understand the reactions in a reverse sense: that is, C ← A + B, where C is the desired functional group. Students tend to have difficulty “thinking backwards”, and many find the transition to the retrosynthetic approach to be quite difficult (6, 7). For organic chemistry courses using texts arranged by mechanistic class (8–10), the same problem exists in that the students do not have exposure to organic reactions in a format that facilitates retrosynthetic problem solving. A second, related problem (11) with which most organic chemistry students struggle is the inability to predict chemistry on the basis of reaction mechanism. Problems understanding mechanisms seem to stem from lack of repetition and inability to visualize the step-by-step sequence of bond making and bond breaking events within the reaction. Creating a Functional Group Transformation Notebook Over the past few years, students in the organic chemistry course taught by one of us (RWH) have been given an ongoing out-of-class assignment that has enabled them to overcome both of the aforementioned difficulties. Starting in the middle of the first semester of organic chemistry—where treatments of reactions of alkyl halides and reactions of alkenes are first introduced—students are asked to begin constructing a “functional group transformation” notebook, or FGT. The notebook (a three-ring binder) is organized by “functional group formed”. For example, when reactions of alkenes are addressed in lecture and acid-catalyzed hydration, hydroboration, and oxymercuration–demercuration are presented, the students log these reactions in their FGT notebook under the heading “reactions that yield alcohols”. The next alkene reaction addressed, HBr addition, is logged under a new heading entitled “reactions that yield alkyl halides”. As the course proceeds, lectures are patterned after the style of the chosen text (2) whereby reactions of the various
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functional groups are addressed, and the students continually add these reactions into their FGT notebook in a backward, or reactions that yield context. This approach results in students’ constructing a compendium of reactions structured in a fashion that is consistent with that utilized in several synthetic serials and monographs (12, 13) with the additional added advantage of possessing detailed mechanisms. Each reaction logged within the FGT notebook has a required format. Students must:
• Number the reaction
• State the nature of the transformation (i.e., alkene ⇒ alcohol)
• Write the generic scheme for the reaction
• Present an example of the reaction
• Write out the complete mechanism for the reaction
• Write out any key statements regarding the reaction that were addressed in class (i.e., Markovnikov addition, anti addition, can rearrange, etc.)
By the middle of the second semester of organic chemistry, where the retrosynthetic approach is addressed in full, the students have a notebook organized by functional group transformation under 15 headings: reactions that yield alkyl halides, alkanes, alkenes, alkynes, alcohols, ethers, esters, ketones–aldehydes, acids, amines, amides, aromatics, nitriles, acid derivatives; and miscellaneous reactions). Throughout both semesters of organic chemistry, students are adding new entries into their FGT notebook after each lecture. As new reactions are addressed, students continue in the development of the FGT, which is an actively growing, on-going document. A copy of the student’s new FGT notebook entries is collected and graded on an announced and regular basis. This way, a mechanism is in place to ensure that students are working in a consistent, daily fashion. Wilson and coworkers have suggested (14) a related and useful project that is also designed to assist organic chemistry students in organizing their reactions. Our approach differs in these particular ways:
• We require a specific format
• Our format requires students to include mechanistic details and key points
• We stress both the construction of the FGT notebook and also using the notebook as a resource for students to solve real-time, in-class synthesis problems
• We grade the FGT notebook to ensure accountability
• Our FGT notebook approach differs in both scope and scale
Journal of Chemical Education • Vol. 85 No. 1 January 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
In the Classroom List 1. Advantages of Constructing of the FGT Notebook
List 2. Advantages in Possessing the FGT Notebook as a Resource
1.
Students are effectively recopying their notes after each class, and they do so in a different format so that the exercise is that much more efficacious
1.
The FGT notebook is an organized compilation of every pertinent reaction addressed in the full-year course, which is a resource of great value in and of itself
2.
Students are reviewing mechanisms after every lecture and recopying from their notes all the key mechanistic aspects of each reaction
2.
The FGT notebook serves as an outstanding resource for reviewing for exams after the formal course has been completed (MCAT, PCAT, DAT, etc.)
3.
Students are, in an ongoing sense, learning to think about organic reactions in both the forward and the reverse (retrosynthetic) sense, from the middle of the first semester of organic chemistry forward
4.
Students use the FGT notebook to solve synthetic problems both in class and in homework, thus establishing connectivity between the reactions covered in class and the solving of synthesis problems
5.
As the number of synthesis problems solved increases, student dependency upon the FGT notebook to solve problems is reduced
6.
Students testify that their note-taking and organizational skills and their general study habits have improved markedly as a result of having constructed a FGT notebook
The advantages to students enrolled in an organic chemistry course that requires a FGT notebook are numerous. We have summarized them in two distinct categories, based on the benefits to students from the process of creating the FGT notebook and the benefits to students of using the FGT notebook as a resource. See Lists 1 and 2 for details. Literature Cited 1. Bruice, P. Y. Organic Chemistry, 5th ed.; Pearson Education, Inc.: Upper Saddle River, NJ, 2007. 2. Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry, 5th ed.; W. H. Freeman and Company: New York, 2007. (We adopted this text, which organizes reactions by functional groups.) 3. Solomons, T. W. G.; Fryhle, C. B. Organic Chemistry, 8th ed.; John Wiley and Sons, Inc.: Hoboken, NJ, 2004. 4. Wade, L. G. Jr. Organic Chemistry, 6th ed.; Pearson Education, Inc: Upper Saddle River, NJ, 2006. 5. Corey, E. J.; Cheng, Z. M. The Logic of Chemical Synthesis; John Wiley and Sons: Hoboken, NJ, 1995.
6. Cannon, K. J.; Krow, G. R. J. Chem. Educ. 1998, 75, 1259. 7. Levy, I. J. J. Chem. Educ. 1988, 65, 853. 8. Hornback, J. M. Organic Chemistry, 2nd ed.; Thomson Brooks/ Cole: Belmont, CA, 2006. 9. Smith, J. G. Organic Chemistry, 1st ed.; Mc-Graw-Hill: New York, 2006. 10. Fox, M. A.; Whitesell, J. K. Organic Chemistry, 3rd ed.; Jones and Bartlett Publishers: Sudbury, MA, 2004. 11. Bhattacharyya, G.; Bodner, G. M. J. Chem. Educ. 2005, 82, 1402. 12. Larock, R. C. Comprehensive Organic Transformations: A Guide to Functional Group Preparations, 2nd ed.; John Wiley and Sons, Inc.: Hoboken, NJ, 1999. 13. Smith, M. B. Compendium of Organic Synthetic Methods, Vol. 8; John Wiley and Sons, Inc.: Hoboken, NJ, 1995. 14. Esteb, J. J.; Magers, J. R.; McNulty, L.; Wilson, A. M. J. Chem. Educ. 2006, 83, 1807.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Jan/abs88.html Abstract and keywords Full text (PDF) Links to cited JCE articles Supplement Example index for the FGT notebook (with 15 functional groups sorted by “reactions that yield”) Example of a functional group notebook category (detailing the 12 reactions that yield alkyl halides) Example application of the FGT notebook (three-step retrosynthetic problem worked from start to finish)
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 1 January 2008 • Journal of Chemical Education
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