The exercise starts with the microscale SN2 synthesis of 1-bromobutane from 1-butanol as described by Williamson (8). The students complete the synthesis and place one drop of the distilled product in a screw capped vial. The vials are then sealed, labeled with the students name and taken to the mass spectrometry laboratory by a teaching assistant.

Students are instructed to sign up for a 20-min block of time over the next few days in order to analyze their sample. When the student arrives at the laboratory, he or she adds 1 ml CH2Cl2 to the sample and injects 0.3 microliters of the solution into the gas chromatograph. The samples typically contain the 1-butanol starting material and the 1-bromobutane product along with traces of dibutyl ether. The figure shows a mass chromatogram along with the mass spectra of the starting material and product from an actual student run. For this analysis to be applicable to large numbers of students, the gc separation must be as rapid as possible. We have been able to analyze each sample in 6 minutes on a 30 m DB-5 capillary column with the following temperature program: 70 oC for 1 min, 70-80 oC at 10 oC/min, 86-140 oC at 67.5 oC/min, 140-210 oC at 70 oC/min, and 210 oC for 1 min. A mass range of 20-200 amu is scanned with a solvent delay of 2 min. Under these conditions each analysis takes the student about 10 min and two students are scheduled per 20 min block.

Since the instrument is under computer control, students operate the computer during the run. As the peaks appear on the mass chromatogram, their mass spectra are obtained and the student decides which corresponds to product and evaluates product purity and the structure of impurities. There is ample time to display all spectra, conduct library searches, and print data. This relatively simple laboratory exercise has the advantage of allowing each student to carry out an analysis on his or her own product. The fact that a brominated product is obtained introduces a discussion of isotopic patterns in mass spectrometry. The experiment is scheduled to coincide with the lecture discussion of spectroscopic structure determination and after SN2 reactions have been covered. One of our mass spectrometer satellite data stations is interfaced with a "3-gun" projector in a large lecture hall allowing the display of actual mass spectra from our instrument to lecture sections.

Acknowlegement

Literature Cited

1. Brush, R. C.; Rice, G. W. J. Chem. Educ. 1994, 71, A293-A294.
2. Asleson, G. L.; Doig, M. T.; Heldrich, F. J. J. Chem. Educ. 1993, 70, A290.
3. Novak, M.; Heinrich, J. J. Chem. Educ. 1993, 70, A150. (b)
4. Novak, M.; Heinrich, J.; Martin, K. A. J. Chem. Educ. 1993, 70, A103-104.
5. Harman, C. S.; Myers, D. P.; Rittle, K. J. J. Chem. Educ. 1991, 68, 438-42.
6. Mabbott, G. A. J. Chem. Educ. 1990, 67, 441-5.
7. Hill, D. W.; McSharry, B. T.; Trzupek. J. Chem. Educ. 1988, 65, 907-10.
8. Williamson, K. L. Macroscale and Microscale Organic Experiments, 2nd ed.; D. C. Heath: Lexington, MA, 1994; pp 247-51.