Curtin-Hammett analysis

This system, however, is much more complex than the simple description in Figure 5.45 suggests. The proper analysis of such systems has to involve the Curtin-Hammett analysis of interconversion of reactive and unreactive conformers and the evolution of stereoelectronic effects along the interconnected reaction pathways. The critical examination of APL theory by Perrin also suggested that the role of conformational equilibria of reactive species, the involvement of syn-periplanar lone pairs, and the different stability of products should be included in the analysis. We will continue our discussion of cooperativity and anti-cooperativity between stereoelectronic effects in Chapter 11. 

Figure 5.12 Curtin-Hammett analysis for (kcalmoh 298K) are with respect to sep-the relative energies of the four mechanisms arated substrate and catalyst (PMejAu+) for the [3,3]-rearrangement of vinyloxy- computed at the B3LYP/LANL2DZ-CH2CI2-...

It is instructive to perform a similar kinetic analysis on the Taguchi system in Sect. 2.4. In view of the Curtin-Hammett principle the product ratio (RRR)-39 (SSR)-39 need not reflect the diastereomer ratio (SR)-2n (RR)-2n (as Taguchi and coworkers assumed it did) [31]. However, when 2n was generated at 67 °C, both benzaldehyde and acetaldehyde gave the same ratio (5 95, RRR SSR) of the diastereomers of the amino alcohols 39, suggesting that the assumption made by Taguchi and coworkers is correct, that Eq. 32 applies, and that RR-2n and SR-2n... 

The Curtin-Hammett principle (see below) applies to this scheme when the rate constants for product formation K and 2 are small relative to rate constants for interconversion over the reactants and intermediates k, k k- and k-2 (in other words, when I j and 1 2 ate in rapid equilibrium). A kinetic analysis of such a process shows that the selectivity depends only upon the free-energy difference between the transition states [ZMSfl and [ -f f]. The ratio of the diastereoi-someric primary products is given by the same relationship as before ... 

Olefin polymerization is not a simple single-step olefin insertion process it involves complex kinetics and multiple equilibria. Insertion is preceded by olefin complexation (Scheme 7.2a) or olefin complexation coupled with counterion displacement (Scheme 7.2b). In view of this complexity, how can the use of barrier differences be justified The use of barrier height differences arises from the Curtin-Hammett principle. The Curtin-Hammett principle is a kinetic analysis that describes product distributions for reactions involving a pair of equilibrating reactants or intermediates, each capable of forming a product. The stereodifferentiation of general isotactic polymerization can be... 

Seeman, J. I. The Curtin-Hammett Principle and the Winstein-Holness Equation. New Definition and Recent Extensions to Classical Concepts /. Chem. Educ. 1986, 63, 42-48. Winstein, S. Holness, N. J. Neighboring Carbon and Hydrogen. XIX. rerf-Butylcyclohexyl Derivatives. Quantitative Conformational Analysis /. Awj. Chem. Soc. 1955, 77, 5562-5578. Curtin, D. Y. Stereochemical Control of Organic Reactions. Differences in Behavior of Diastereoisomers. I. Ethane Derivatives. The Cis Effect Rec. Chem. Pro ir. 1954, 15, 111-128. An alternative to the Curtin-Hammett argument presented on page 295 is that the epoxide reacts with thiophenoxide from conformation 64b such that the product is bom in the B ring boat (or twist-boat) conformation of 65b. 

The Curtin-Hammett principle is an old example of the simplicity of an energy-based analysis instead of one using rate constants. This principle states that the selectivity can be defined by the relative height of the selectivity determinii transition states, which is conceptually easier than having to take into account four rate constents ... 

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