Thermodynamics vs kinetic control

Stereochemistry of Diels-Alder Reactions. Thermodynamic vs. Kinetic Control... 

The reader may wish to revisit the discussion of thermodynamic vs. kinetic control provided in Chapter 1. 

Thermodynamic vs. Kinetic Control in the Formation of Isopropylidene Acetals from Butane-1,2,4-triols and Propane-1,2,3-triols... 

In the description of crystals and crystal structures the two terms/om and habit have very specific and very different meanings. Form refers to the internal crystal structure and etymologically is the descendant of the Greek morph. Hence, polymorph refers to a number of different crystal modifications or different crystal structures, and the naming of different structures as Form F or a Form follows directly from this definition and usage. As we have seen above, the difference in crystal structure is very much, although not exclusively, a function of thermodynamics. Certainly, only the structures which are thermodynamically accessible can ever exist, but there often is a question of thermodynamic vs kinetic control over which particular structure may be obtained under any particular set of crystal growth conditions. 

Balzer, W., 1982. On the distribution of iron and manganese at the sediment/water interface thermodynamic vs. kinetic control. Geochimica Cosmo-chimica Acta, 46 1153-1161. 

An interesting example of thermodynamic vs kinetic control was observed in the temperature dependence of carboxylation of methylcyclopentane in the presence of HF-SbFs (90). Carboxylations were carried out by bubbling CO through the reaction mixture either at —40°C or 0°C followed by quenching the resulting solution with ethanol. A reaction at -40°C yields quantitatively ethyl... 

This behaviour was rationalized by thermodynamic vs kinetic control, which is further supported by molecular-mechanics and quantum-mechanical calculations. ... 

AG, Free Energy of Activation Rate Constant Upper Limit on Concentration Diffusion-Controlled Limit Dropping the AG by 1.36 kcal/mol (5.73 kJ/mol) Increases the Rate of Reaction Tenfold at Room Temperature Reasonable Rate at 25°C Half-Life Lifetime of an intermediate Rate-Determining Step Transition State Position Reactivity vs. Selectivity Thermodynamic vs. Kinetic AG = AH -TAS, Enthalpy of Transition Entropy of Transition Stabilization of Intermediates Stabilization of Reactants... 

The voltammetric data and other relevant kinetic and thermodynamic information are summarized in Table 2. While for X = H the initial ET controls the electrode rate, as indicated by the rather large p shift and peak width, the electrode process is, at low scan rates, under mixed ET-bond cleavage kinetic control (see Section 2) for X = Ph, and CN. Although the voltammetric reduction of these ethers is irreversible, in the case of the COMe derivative, some reversibility starts to show up at 500 Vs in fact, this reduction features a classical case of Nernstian ET followed by a first-order reaction. The reduction of the nitro derivative is reversible even at very low scan rate although, on a much longer timescale, this radical anion also decays. 

Table V summarizes the results of both this investigation and those reported in the literature. The amount of ring metalation and relative ratios of isomers vary somewhat according to the procedure used and on standing. This is evidently a case of kinetic control vs. thermodynamic control, as pointed out by Broaddus (18). Therefore the procedure for metalation affected the initial amount of ring-isomer formation directly as expected in a kinetically controlled reaction that involves temperature of metalation, amount of TMEDA, and subsequent treatment or storage of the product solution. A recent report discusses a similar system of anion equilibration between m- and p-xylyllithium with TMEDA, and anion equilibration between the meta and benzyl positions of ethylbenzene using TMEDA or N,N,N/,N, N"-pentamethyldiethylenetriamine (PMDET) (20).

The elimination of FlCl from the diester 331 with base afforded a mixture of the diesters 332 and 333, both as E-Z mixtures, together with 334. During the course of contact with the base, the composition of the product mixture was determined by proton NMR spectroscopy and GLC. For the 0L,p- and j5,y-unsaturated esters, plots of composition vs time cross, showing their interconvertibility. Formation of the product 332 is kinetically controlled, and both 333 and 334 are the thermodynamically controlled products. At final equilibrium, the mixture of unsaturated esters 332-333-334 had the composition 12 84 4 Similar prototropic changes had been observe earlier during the dehydrochlorination of diethyl (2-chloropentyl)phosphonate. ... 

Figure 1.5 Three regimes of reaction control, (a) kinetic vs. thermodynamic control (b) kinetic vs. tunneling control. ...

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