ENRICHING THE ORGANIC CHEMISTRY LABORATORY: A DIRECTORY OF GUIDED INQUIRY ORIENTED EXPERIMENTS
For this experiment and many others, a much newer site has been uploaded: http://murov.info/orglab/orglab.htm
In recent years, the organic chemisty laboratory instructor has been provided a choice of several new generation organic laboratory manuals. Most have detailed and excellent sections on techniques and spectroscopy and a representative selection of experiments. The addition of micro and small scale experiements enable students to perform experiments in shorter periods of times while using much small quantities of materials. This substantially decreases chemical and disposal costs while providing a safer envirnoment and the opportunity to perform more experiments.
However, there is still considerable room for improvement.The experiments in introductory and general chemisty laboratory courses usually include the measurement or determination of some quantity unknown to the student. It seems to be regressive then that in their second chemistry course, organic chemistry, students use most of their time verifying information given in the laboratory manual. Typically, experimental instructions include not only detailed manipulative directions but also physical and spectroscopic properties of the expected product. For educational and motivational reasons, the laboratory should involve more than a technique learning experience. Some aspects of a research atmosphere are needed with strong connections made to material covered in the lecture portion of the course. This must be accomplished without producing an unsafe and unmanageable laboratory environment. Students need and undoubtedly want the challenge of an exploration rather than continuous verification. [For a controversial paper on the these issues by a late colleague and friend, see Miles Pickering, J. Chem. Ed., 1988, 65, 143] In the last couple of years, two new organic laboratory manuals that are worthy of inspection because of their guided inquiry approach have been published: Mohrig, J. R., Hammond, C. N., Morrill, T. C. and Neckers, D. C., Experimental Organic Chemistry, Freeman, N.Y., 1999; Lehman, J. W., Operational Organic Chemistry, Prentice-Hall, N.J., 1999.
The purpose of this web site is to establish a directory of organic laboratory experiments that include exploration and are relatively safe, inexpensive and manageable. This directory will include references to journals, organic laboratory manuals and web sites as well as a small number of complete laboratory experiments that are at least partially guided inquiry or discovery oriented in nature. Guidelines that will be used to select the experiments are:
1. Early in the course, most experiments emphasize the learning of techniques for the determination of physical properties such as melting point, boiling point, density and refractive index. Each of these technique experiments should include at least one unknown. At this stage however, it is probably wise to provide a limited list of possible unknowns.
2. The amount of product information provided in the experiment should be minimal. Learning to use chemistry resources is a very important part of the laboratory experience. Students should have to find physical, chemical and spectroscopic properties using readily available references including handbooks, spectroscopic collections and the internet.
3. Syntheses should be designed or selected so that it is posssible to write logical mechanisms to more than one possible product. Students can discover or at least test rules or predictive tools such as Markovnikov's, Saytzev's and aromatic substitution orientation by determining product structure.
Odor of Optical Isomers. Based on the elegant
research of L. Friedman and J. G. Miller (Science, 1971,
172, 1044) and G. F. Russel and J. I. Hills (Science, 1971,
Pickering and I wrote an article for JCE about the separation and purification of the carvones from spearmint and caraway oils and a comparison of their properties. Subsequent articles have added to the possible techniques useful for the separation. This experiment has been incorporated into many of the currently used organic chemistry lab manuals. Unfortunately, from my perspective, almost all instructions have made the experiment cookbook in nature. For safety purposes, there is no need to provide anything more than instructions for separation and purification and a list of properties that should be measured. Properties that can be determined are boiling point, density, refractive index, ir, nmr, gas chromatographic retention times, very careful smell determinations and optical rotations. For the optical rotations, we supply polarimeter tubes already filled with the two carvones as polarimetry usually requires more material than the students obtain. An additional option for this experiment after the identity of the compounds has been determined or given is to have students perform an internet search for d-carvone and l-carvone for their properties. It is interesting to note, however, that the reported LD50 values for the two are 3.7 mg/kg and 1640 mg/kg respectively. The very high reported toxicity of d-carvone was unexpected and was hard to believe especially in light of its use as a flavoring. This apparent discrepancy led me to make an inquiry to the FDA and they responded that a typographical error from the original data has been sustained during subsequent publications of the data. The correct LD50 is apparently 3.6 g/kg, a value much more consistent with that of its enantiomer and with its acceptable use in foods.
Two possible approaches to this experiment are the following:
1. Have students select a partner and give one student spearmint oil and the other caraway oil. Each student then performs the separation, purification (by distillation or chromatography) and property determinations independently. Students then compare the properties of each product and are asked to make appropriate conclusions.
2. A shorter option involves supplying each partner with one of the two carvones. Relatively pure samples of both carvones are commercially available at costs that are not prohibitive. For this option, each student then does all the property determinations eliminating the not too trivial separation and purification portion of the experiment. Another option is to use the two limonenes instead of the carvones however the smell differentiation is questionable.
S. L. Murov and J. Pickering, J. Chem. Ed., 1973,
R. H. Mitchell and P. R. West, J. Chem. Ed., 1974, 51, 274.
D. L. Garin, J. Chem. Ed., 1976, 53, 115.
Laboratory Manual Examples
Bromination of Cinnamic Acid. After bromination, the melting point of the product and an analysis of possible mechanisms leads to the conclusion that the addition had to have been anti. Extreme care must be exercised when using bromine and this part of the experiment must be performed in a hood.
J. W. Lehman, Operational Organic Chemistry, a Laboratory Course, Prentice Hall, 2 nd ed., 1988, 191 - 199.
An interesting example of a reaction with potentially different product structures involves the addition of dichlorocarbene to 2-methyl-1-buten-3-yne. For instructions for this two step synthesis, jump to http://murov.info/carbene.htm
This site (orginally uploaded 1/16/98) is in its very early stages of construction and it is anticipated that this site will be continually updated as appropriate experiments are located. If you are aware of references to lab experiments of this type or would like links established to sites that have guided inquiry experiments, please send an e-mail message to: firstname.lastname@example.org
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