Kinetics versus

Basic Mechanistic Concepts Kinetic versus Thermodynamic Control, Hammond s Postulate, the Curtin-Hammett Principle... 

SECTION 4.4. BASIC MECHANISTIC CONCEPTS KINETIC VERSUS THERMODYNAMIC CONTROL, HAMMOND S POSTULATE. THE CURTIN-HAMMETT PRINCIPLE... 

The idea of kinetic versus thermodynamic control can be illustrated by discussing briefly the case of formation of enolate anions from unsymmetrical ketones. This is a very important matter for synthesis and will be discussed more fully in Chapter 1 of Part B. Most ketones, highly symmetric ones being the exception, can give rise to more than one enolate. Many studies have shown tiiat the ratio among the possible enolates that are formed depends on the reaction conditions. This can be illustrated for the case of 3-methyl-2-butanone. If the base chosen is a strong, sterically hindered one and the solvent is aptotic, the major enolate formed is 3. If a protic solvent is used or if a weaker base (one comparable in basicity to the ketone enolate) is used, the dominant enolate is 2. Enolate 3 is the kinetic enolate whereas 2 is the thermodynamically favored enolate. 

FIGURE 6.3 Free energy profile illustrating kinetic versus thermodynamic control of product. The starting compound (A) can react to give either B or C. 

Swackhammer, D.L. and R.S. Skoglund. 1993. Bioaccumulation of PCBs by algae kinetics versus equilibrium. Environ. Toxicol. Chem. 12 831-838. 

Blaustein It seems to me to be a question of kinetics versus the steady-state condition. In the steady-state you will probably have the same amount of Ca2+ there, if you wait long enough, even though uptake is slower. 

For those readers requiring further information on the factors effecting the kinetic versus diffusion control of the SSP process, this has been reported by several authors (for example, kinetic aspects [4, 8, 20] and diffusion-influenced aspects [5-7, 9, 11-13, 15]). 

Directions for Future Work. The measurement of rates of proton transfer from a single acid to more bases differing only in thermodynamic base strength should allow the construction of BrjSnsted plots of kinetic versus thermodynamic acidity. The bases we have used at this early stage of development of the subject have involved different proton acceptor atoms and cannot be so used (although comparison of the Et N transfer rates of... 

Schicks, J.M. Ripmeester, J.A. (2002). The Coexistence of Two Different Methane Hydrate Phases under Moderate Pressure and Temperature Conditions Kinetic versus Thermodynamic Products. Angew. Chem. Int. Ed., 43,3310-3313. 

This chapter provides a general discussion of kinetics versus thermodynamics, chemical kinetics versus geochemical kinetics, and an overview of the basics of various kinetic processes and applications. Subsequent chapters will provide in-depth development of theories and applications of specific subjects. The purpose of the overview in this chapter is to provide the big picture of the whole field before in-depth exploration of the topics. Furthermore, this chapter is a standalone chapter that may be used in a general geochemistry course to introduce kinetics to students. 

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