Thermodynamic versus kinetic issue

Many reviews deal with the main mechanistic aspects of the metathesis reaction [10]. There are three basic metathesis reactions (apart from polymerization reactions) the ring-closing metathesis (RCM), the cross-metathesis (CM) and the ringopening metathesis (ROM) [11]. Among the fundamental aspects that govern the reaction course, the thermodynamic versus kinetic issue is particularly important when considering the application of RCM to the construction of macrocydes. 

Careful product and kinetic studies for selected electron-deficient alkenes, electron-rich dienes and vinyl-substituted aromatic systems have provided some clarification of the [2 + 2] versus [2 + 2] cycloaddition issue. The thermodynamically favored product can often be anticipated on structural grounds. Reactions of TCNE with vinyl-substituted benzenoid aromatics, protoporphorins or heteroaromaticsgive [2 + 2] products, but for some styrenes the [2 + 4] addition may be kinetically favored. p-Methoxystyrene and TCNE react to form a charge-transfer complex which leads reversibly to the Diels-Alder product, and eventually to the finally isolated [2 + 2] adduct. An isomer of di-cyclopentadiene shows the same pattern, with the initially formed Diels-Alder adduct giving rise to a [2 + 2] adduct. 

Before commencing this discussion, it is appropriate to consider briefly the issue of kinetic versus thermodynamic control in the reactions of preformed Group I and Group II enolates and to summarize the structure-stereoselectivity generalizations that have emerged to date. It is now welt established that preformed lithium, sodium, potassium and magnesium enolates react with aldehydes in ethereal solvents at low temperatures (typically -78 °C) with a very low activation barrier. For example, reactions can often be quenched within seconds of the addition of an aldehyde to a solution of a lithium enolate. ... 

For any sort of linear free-energy correlation, a very interesting issue to explore is that of using the pK of the nucleophile rather than the reaction exothermicity itself Not untypically, discussions of nucleophilicity (a kinetic quantity) versus basicity or proton affinity (a thermodynamic quantity) result. In principle, no reason exists to use the pK of the nucleophile rather... 

One of the first assumptions in our economic considerations was that all the technological challenges were met. This remains, at the moment of writing, uncertain. In the above discussion, a number of issues have passed, such as sealing technology, thermodynamic phase stability of the cubic perovskite versus brownmillerite, and kinetic demixing. In relation to this, we have not mentioned creep resistance as yet. For SCF, this was shown to be very low [40], which is likely to be the case for BSCF as well. 

To tackle this problem, you have to invoke the principles of kinetic versus thermodynamic control (review Sections 11-6, 14-6, and 18-2) that is, which enolate is formed faster and which one is more stable Divide your team so that one group considers conditions A and the other conditions B. Use curved arrows to show the flow of electrons leading to each enolate. Then assess whether your set of conditions is subject to enolate equilibration (thermodynamic control) or not (kinetic control). Reconvene to discuss these issues and draw a qualitative potential-energy diagram depicting the progress of deprotonation at the two a sites. 

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