This literature discussion is based on a paper by Bill Jones and Frank Feher (J. Am. Chem. Soc., 1986, 108, 4814-4819). In this paper, they study the activation of aromatic C-H bonds by a rhodium complex. Through careful experimental design, they were able to examine isotope effects on the selectivity of the reaction. Analysis of the rate data allowed them to prepare a reaction coordinate free energy diagram. This paper also introduces the effects of C-H bond breaking in early or late transition states on the vibrational energy spacing at both ground and excited states. The paper is a good way to bring kinetic isotope effects into the classroom. The paper also introduces the concept of deuterium labeling experiments and what that information can tell you.
An important aspect of this paper, and what makes it so interesting, is that they are able to get two kinetic isotope effects, one for each step of the reaction. From these two KIEs alone they are able to determine the unexpected rate-determining step of the reaction. It is a triumph of mechanistic investigation into intermediates that are undetectable.
This LO presents a series of guided reading questions that help a student approach and understand the material presented in the paper in a more thorough way. Part one is a guided inquiry that allows the students to derive and understand differing zero point energies for proteated and deuterated compounds. Part two guides students through the results presented in the paper to help them better understand how experimental data can be used to understand the mechanism of a chemical reaction. There is more to the paper than kinetic isotope effects, but that is the focus I chose while developing it. The LO is suitable for junior or senior undergraduates in an organometallics course or unit within an inorganic course.
I would like to acknowledge Ryan Pakula and Joanne Redford from my Chem 165 course in 2008 who wrote early versions of some of the questions about vibrational states, and a careful critical read by Nancy Williams, who understands this stuff at a much deeper level than I do.