For many decades, the concept of a "rate-determining step" has been of central importance in understanding chemical kinetics in multistep reaction mechanisms and using that understanding to advantage. Yet a rigorous method for identifying the rate-determining step in a reaction mechanism was only recently introduced, via the "degree of rate control" of elementary steps. By extending that idea, we argue that even more useful than identifying the rate-determining step is identifying the rate-controlling transition states and the rate-controlling intermediates. These identify a few distinct chemical species whose relative energies we could adjust to achieve a faster or slower net reaction rate. Their relative energies could be adjusted by a variety of practical approaches, such as adding or modifying a catalyst, modifying the solvent, or simply modifying a reactant's molecular structure to affect electronic or steric control on the relative energies of the key species. Since these key species are the ones whose relative energies most strongly influence the net reaction rate, they also identify the species whose energetics must be most accurately measured or calculated to achieve an accurate kinetic model for any reaction mechanism. Thus, it is very important to identify these rate-controlling transition states and rate-controlling intermediates for both applied and basic research. Here, we present a method for doing that.

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Page 4191. The absolute stereochemistry of compounds in Table 2 has been revised on the basis of an empirical model proposed previously and by analogy to related π-allyl reactions. 13 For entry 7, the absolute stereochemistry of the sulfamate product was determined following its conversion to the known (R)-tert-butyl-1-hydroxybut-3-en-2-ylcarbamate; the stereochemical result is in accordance with the empirical model. Structures depicted in the Supporting Information should reflect the changes made in the corrected version of In this paper, we extended Campbell's "degree of rate control of each elementary step" to similarly define the "degree of rate control of each intermediate" for the general kinetic analysis of any multistep reaction mechanism. We did not realize that a very similar extension had already been made by Kozuch and Shaik, 1 who introduced the "degree of turnover frequency control of each intermediate" for analyzing multistep catalytic mechanisms. Kozuch and Shaik also had previously presented many useful applications of this concept, and ideas that evolve from it, 1,2 some of which are similar in some ways to points made in our paper. We sincerely apologize for not having cited their two pioneering papers in these very important respects. Table 2. Pd-Catalyzed Asymmetric Allylic Amination a Reactions were performed in THF using 2.5 mol % Pd 2 (dba) 3 · CHCl 3 , 7.5 mol % (S,S)-L 1 at 0.2 M; yields are based on limiting amounts of nucleophile 2. Literature Citedb Reaction conducted using (R,R)-L 2 . c Reaction conducted in dioxane.

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