Since the students became familiar with cyclic voltammetry, one trend of interest involves the ionization potential of the substituted ferrocenes. One student project involved a comparison of several known substituted ferrocenes (6) and their gas phase models (Figure 1 and Table 2). The gas phase models were used since the expected solvent dependence has not been observed using the CAChe system due to initial limitations with project leader. The initial calculated ionization potentials were adjusted by subtracting 7.647 eV. This sets the ferrocene/ferrocenium couple at zero as is customary (6). These values and a least squares regression plot were then plotted. In general, a downward trend in the least squares regression is observed with the more easily reduced ferrocenes containing electron withdrawing substituents having positive ionization potentials. Conversely, the more easily oxidized ferrocenes with electron donating substituents are calculated with negative ionization potentials. Deviations from experimental data may be accounted for since the student was comparing gas phase ferrocene models and acetonitrile ferrocene electrochemistry (6).
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Fig. 1. Student CAChe Project
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Table 2 Student CAChe Project
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ConclusionThe incorporation of an iterative question into each of our advanced inorganic undergraduate laboratories has allowed students to plumb the depths of their chemical knowledge and to acquire new tools that improve their use of the scientific method. The students enjoy the high success rate of the ferrocene/acetylferrocene lab. They also appreciate the chance to acquire new synthetic techniques such as the use of Schlenk techniques. In addition, the use of novel instrumental analysis such as electrochemistry is beneficial to their overall undergraduate education. They seem to thrive on the diverse exposure and the opportunity to stretch themselves. This allows them to become excited about chemistry and like the experiment that they are conducting, they come full circle and view chemistry in a new light as a useful, valuable tool. The addition of the iterative question to a classical laboratory can therefore provide an additional richness to the traditional wet chemistry.
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AcknowledgmentsResearch supported by NSF under Grants # DUE-9452023 and DUE-9452131.
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Literature Cited1. Kauffman, George B. J. Chem. Educ. 1983, 60, 185.2. Kealy, T. J.; Pauson, P. L. Nature 1951, 168, 1039.3. Jolly, W. L., The Synthesis and Characterization of Inorganic Compounds, Prentice-Hall: New Jersey, 1970.4. Bozak, R. E. J. Chem. Educ. 1966, 43, 73.5. Szafran, Z.; Pike, R. M.; Singh, M. M., Microscale Inorganic Chemistry, Wiley: New York, 1991.6. Geiger, William E. J. Organomet. Chem. 1990, 22, 142.7. Wade, Leroy G. J. Chem. Educ. 1978, 55, 208.8. Rosenblum, Myron, Chemistry of the Iron Group Metallocenes: Ferrocene, Ruthenocene, Osmocene Part One, Interscience Publishers: New York, 1965.