1995 Syntex Award Lecture Correlation and prediction of rate constants for organic reactions

Abstract

Abstract:Marcus theory provides a framework for correlating rate and equilibrium constants, and thus the possibility of predicting rate from structure. This had been successful for a number of simple reactions, including the addition of hydroxide to carbonyl compounds, enolate formation from carbonyl compounds, and aldol addition and elimination reactions. The theory can be extended, as Multidimensional Marcus Theory, to cover concerted reactions such as E2 eliminations, the water-mediated proton switch, or the breakdown of the tetrahedral intermediate in amide hydrolysis. We have now found that Marcus theory can be applied not only to inter-molecular reactions but also to intra-molecular reactions. This is illustrated for aldol condensation and esterllactone formation.Key words: Marcus theory, concerted reactions, intramolecular reactions, aldol condensation, ester formation, proton transfer.Resume : La thCorie de Marcus offre un s y s t h e pour Ctablir des corrClations entre les constantes de vitesse et dlCquilibre et, de ce fait, la possibilitC de faire des pridictions relatives aux vitesses ii partir des structures. Cette approche a Ct C couronnke de succks pour un certain nombre de rCactions simples, y compris l'addition de l'ion hydroxyde ii des composks carbonylks, la formation d'Cnolates 5 partir de composCs carbonylks et les rkactions d'addition et d'klimination aldoliques. On a ktendue la thiorie, sous la forme de la thCorie multidimensionnelle de Marcus, pour couvrir les rCactions concertkes, comme les Climinations E2, 1'Cchange de protons avec l'eau comme mCdiateur ou 1adCpyramidalisation de l'intermkdiaire tCtraCdrique lors de l'hydrolyse des amides. On a trouvC que la thCorie de Marcus peut &tre appliquCe, non seulement aux rCactions inter~nolCculaires mais aussi aux rCactions intramolCculaires. On illustre ce point par la condensation aldolique et le formation d'esterllactone.

[2+3] Cycloaddition of Ethylene to Transition Metal Oxo Compounds. Analysis of Density Functional Results by Marcus Theory

“…In the following, we will use the Marcus equation, originally derived for electron-transfer reactions, to relate the activation barriers Δ E ‡ of ethylene [2+3] cycloaddition to a complex LMO 3 to the corresponding reaction energy Δ E 0 . The Marcus approach has been successfully applied to many chemical reactions, , also in a generalized multidimensional version, but failures have also been reported. , Most applications dealt with reactions of organic compounds, also with results obtained from ab initio calculations. , Marcus theory starts from a general schematic reaction profile (see Figure ): two parabolas for reactants and products along a formal reaction coordinate x that ranges from 0 to 1. Assuming the same parabola curvatures for reactants and products, straightforward algebra leads to the desired result: The intrinsic reaction barrier Δ E ‡ 0 , the central parameter of Marcus theory, represents the barrier of a thermoneutral reaction (Δ E 0 = 0) where the transition state is located midway between reactants and products, at x ‡ = 1 / 2 .…”

Hydration of Carbonyl Compounds, an Analysis in Terms of Multidimensional Marcus Theory

“…Rate and equilibrium constants for the addition of water to carbonyl compounds have been shown to follow Marcus theory. − We have examined this reaction several times, starting with a naive and simplified version of Marcus theory 11 and gradually using more sophisticated models: first explicit inclusion of diffusion steps leading to encounter complexes within which actual reaction occurs (when there is a second reactant other than solvent); then explicit allowance for the energetic cost of partially desolvating anions when they are in direct contact with the carbonyl compound . In these earlier treatments different intrinsic barriers were found for the different mechanisms: different models for the work term led to different values for the intrinsic barrier, because the two parameters are correlated.…”

Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD+ Analogues

“…Marcus theory of the relation between rate and equilibrium constants has been applied successfully and widely to proton transfer, hydride transfer, and group transfer as well as electron transfer reactions . Application of a modification of Marcus theory to the hydride transfer reaction shown in eq 1 leads to an interpretation of the Brønsted α, defined as [d(ln k )/d(ln K )] in terms of a parallel (Leffler−Hammond) effect and a perpendicular (Thornton) effect …”