Thermodynamic stability base strength

SX Wang et al. (1998) have developed a parameter, S, to address the susceptibility to amorphization for oxides based on the analysis of glass-forming ability. The S parameter combines three factors the structural connectivity, bond strength, and thermodynamic stability. The use of the three factors is based on a consideration of their affect on the tendency of the damaged regions to recrystallize. The S parameter is defined as ... 

However, a A H calculation usually predicts the C-reacted compound to be thermodynamically more stable than the Z-reacted compound (mainly because of the greater C-Z bond strength in the C-reacted product compared to the C=C in the Z-reacted). However, this does depend on the relative C-E vs. 0-E bond strength. It is important to determine which is the dominant effect, product formation based upon product thermodynamic stability or upon kinetic direction from HSAB theory. To do this we need to determine whether the reaction is under kinetic or thermodynamic control. Figure 9.1 gives a flowchart for the decision for a common ambident nucleophile, an enolate anion (Z equals oxygen). 

Braga et al. [110] studied three polymorphic forms of the cocrystal 4,4 -bipyridine/pimelic acid, forms I, II and III. The three polymorphs presented very similar crystal packings. Nevertheless, small differences among the spectra made possible the distinction of the different forms. From the spectra, it could be determined that the reason of the thermodynamic stability of form II at room temperature was not because of differences in the strength of the hydrogen bond interactions, but due to differences in the crystal packing. It could also be noted from the and experiments that no proton transfer took place from the acid to the base, in the three forms. 

The lone pair of electrons can be broadly described as occupying an sp hybrid orbital of the nitrogen atom, but the precise character of this orbital depends upon the groups linked to the nitrogen atom. Thus the energy of the N—H bond produced, and the thermodynamic stability of the positive ion, depend on the nature of these groups. As a result of this and other factors the strengths of amines as bases vary considerably. 

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