Chemical Education Today edited by Susan H. Hixson
NSF Highlights
National Science Foundation Arlington, VA 22230
Incorporation of FT-NMR throughout the Chemistry Curriculum
Richard F. Jones Sinclair Community College Dayton, OH 45402-1460
by D. Scott Davis* and Dale E. Moore Through funding from the former Instrumentation and Laboratory Improvement (ILI) program of the National Science Foundation and matching funding from Mercer University, our department was able to recently install a Varian Inova 300-MHz broadband Fourier transform nuclear magnetic resonance (FT-NMR) instrument (DUE #9751056). Our use of this instrument comprises a significant part of a broader departmental initiative to integrate computer-interfaced instrumental techniques into all of our courses. In this communication, we specifically outline the approach that we have taken in incorporating FT-NMR throughout all levels of the chemistry curriculum. Many chemistry departments serving primarily (or exclusively) undergraduate students may have continuous wave (CW) NMR instruments collecting dust, believing that these instruments have outlived their usefulness, and our department was no exception. In developing our NMR-based curricular proposal, we found ourselves considering the fate of our CW Varian 360L 60-MHz NMR instrument and planned to retire it. Fortunately, we discovered that the utility of our CW NMR could be renewed with Fourier transform capability through a console upgrade—the EFT spectrometer available from Anasazi Instruments.1 This impressive package converted an archaic, user-unfriendly instrument into a modern, computer-driven workhorse that was ideally suited to introductory, instructional use. Importantly, the greater student throughput of the EFTNMR—1H spectra could be acquired in about three minutes—has enabled a complete laboratory section (ca. 30 students) to easily acquire individual spectra during a three-hour laboratory period. Due to the ease of use of the interface software (WinNuts2), we now include an NMR-based experiment in our first-year chemistry laboratory curriculum.
The calendar placement of the first student experiment with the 60-MHz EFTNMR has been textbook-dependent, but scheduled to coincide with in-class discussions of electronegativity and molecular structure—topics that typically come together in the first-year curriculum in addressing polar molecules. Prior to using the NMR, student familiarity with spectroscopic analysis and instrumentation was established through their use of benchtop UV–visible absorbance instruments, such as the Milton Roy Spectronic 20+. An inclass rudimentary description of 1H NMR preceded the experiment, and student teaching assistants assisted in familiarizing first-year students with the WinNuts instrumental interface in the laboratory. In the experiment itself, first-year students performed an experiment to qualitatively and quantitatively compare the impact of electronegativity and molecular polarity on proton chemical shifts: 1H NMR spectra were obtained for various sealed samples of mono-, di-, and trisubstituted halomethanes.3 This series of compounds was chosen because each compound demonstrated only a single proton resonance. Each student collected the spectrum for one compound in the series; then students worked in groups, pooling their data and making predictions about the expected chemical shifts for “untested” members of the series. We have immediately begun using spectroscopy routinely in the second-year, organic chemistry sequence of courses. Although it is nontraditional, we believe that an early introduction to spectroscopy offers pedagogical advantages over delaying until later in the course sequence. When presenting parallel in-class discussions of both organic functional groups and their expected NMR spectra, students have benefited from NMR characterization in the laboratory as reinforcement of the in-class topical material (1). In the second lab week, organic chemistry students have learned sample prepa-
Table 1. Incorporation of NMR into Each Level of the Chemistr y Curriculum Level
Experiment
Introductor y Chemistr y (Freshman Level)
Study of Electronegativity by Additive Effects of Halogens on Methane
Organic Chemistr y (Sophomore Level)
Basic Identification of Simple Known Organic Molecules by 1H and 13C NMR Identification of Student-Prepared Unknowns throughout the First Semester Transition to 300-MHz NMR; 2D-NMR Lab (COSY, HETCOR, DEPT) Identification of Intermediates and Products from Synthesis Project (1H, 13C, 2D-NMR)
Integrated Laborator y (Junior Level)
Determination of the Structure of an Ester from an Unknown Alcohol and Carboxylic Acid by 2D-NMR (3); Stereochemical Outcome of an Enzyme-Catalyzed Reaction (10); Conformational Analysis of Various Substituted Cyclohexanes (Computational Component Included); Synthesis of a "Molecular Tweezer" and Subsequent Binding Studies (Variable-Temperature 1H NMR); Determination of Magnetic Susceptibilities of Transition Metal Complexes5
Research (Senior Level)
H and 13C NMR of Intermediates and Products; P NMR of Novel Herbicides
1
Cd NMR on Nanoparticle Clusters;
111
31
JChemEd.chem.wisc.edu • Vol. 76 No. 12 December 1999 • Journal of Chemical Education
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Chemical Education Today
NSF Highlights ration and independent spectral data acquisition in determining the structures of two simple organic “unknowns” by 1H NMR and FTIR spectroscopies. (We have used from 20–50 different unknowns representing a variety of aldehydes, ketones, carboxylic acids, and esters.) This experiment has been performed on the 60-MHz instrument and has been preceded by a fairly extensive, in-class discussion of NMR theory. Thereafter, throughout the first semester of organic chemistry laboratory, students have been required to follow up all syntheses with spectroscopic characterization (NMR, IR) of the reaction products they obtain. Our students made the transition from the 60-MHz to the 300-MHz instrument midway through the organic chemistry sequence of courses. Once the use and interpretation of NMR spectroscopy became routine, we introduced advanced NMR techniques. In the second-semester laboratory, all organic chemistry students performed COSY, HETCOR, and DEPT experiments as a demonstration of available structural elucidation tools.4 Following this, students embarked on extended synthetic research projects, attempting to complete two-step syntheses of their own designs (2). At this stage, our organic students regularly use the 300-MHz instrument for 1H and 13C NMR analyses of their products, and some are also able to repeat the more advanced experiments, such as COSY, HETCOR, and DEPT. In a recent change to our laboratory curriculum beyond the second year, we replaced course-specific (or even areaspecific) laboratory courses with a single, “integrated” laboratory course sequence. This sequence emphasizes studentdriven research with investigative projects crossing the traditional chemistry subdisciplines. In this laboratory setting, the NMR instrument becomes important not only as a powerful structural characterization tool, but as an instrumental platform for physical experimentation as well. Specific projects proposed to exploit the power of the 300-MHz FTNMR instrument and to require students to design their own NMR protocols include the synthesis of esters from “unknown” pairs of carboxylic acid and alcohol starting materials with subsequent product characterization by advanced NMR experiments (3); the determination of the magnetic susceptibilities of transition metal complexes by the Evans method (4) with comparison to measurements by the Guoy balance method and by the benchtop magnetic susceptibility balance;5 using chiral shift reagents in the determination
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of the specificity of two dehydrogenases relative to NADH (5); and the variable-temperature (220 to 80° C) analyses of substituted cyclohexanes to determine the barriers for conformational exchange (6). Our undergraduate chemistry major culminates with senior-level research projects using the 300-MHz NMR instrument extensively. Besides employment in the identification of organic intermediates and products, 13C NMR of organic ligands coordinated to colloidal CdS particles has aided in elucidating the molecule-to-surface bonding mode. Heteronuclear experiments have also been undertaken: 111Cd NMR studies on the structure of colloidal CdS particles and 31 P NMR studies on novel herbicides are currently in progress. Table 1 summarizes the incorporation of nuclear magnetic resonance into each level of our chemistry curriculum. Notes 1. Anasazi Instruments, Inc., 4101 Cashard Ave. #103, Indianapolis, IN 46203. 2. Acorn NMR, Inc., 46560 Fremont Blvd. #418, Fremont, CA 94538; http://www.acornnmr.com. 3. This is a locally developed activity utilizing sealed samples of CHCl3, CH2Cl2, CH3Cl, CHBr3, CH2Br2, CH3Br, CHI3, CH2I2, and CH3I. 4. Compounds employed include isopentyl acetate, 4-methyl-2pentanol, and the various methyl substituted hexanols. 5. One such instrument is available from Johnson Matthey Fabricated Equipment, 436 Devon Park Dr., Wayne, PA 19087.
Literature Cited 1. Hugdahl, J. D.; Davis, D. S.; Nichols, K. J. Chem. Educ., submitted for publication. 2. Davis, D. S.; Hargrove, R. J.; Hugdahl, J. D. J. Chem. Educ. 1999, 76, 1127. 3. Branz, S. E.; Miele, R. G.; Okuda, R. K.; Straus, D. A. J. Chem. Educ. 1995, 72, 659. 4. Live, D. H.; Chan, S. I. Anal. Chem. 1970, 42, 791. 5. Mostad, S. B.; Glasfield, A J. Chem. Educ. 1993, 70, 504. 6. Diaz, A.; Radzewich, C.; Wicholas, M. J. Chem. Educ. 1995, 72, 937.
D. Scott Davis and Dale E. Moore are in the Department of Chemistry, Mercer University, 1400 Coleman Avenue, Macon, GA 31207; email:
[email protected] and
[email protected].
Journal of Chemical Education • Vol. 76 No. 12 December 1999 • JChemEd.chem.wisc.edu
