Thermodynamic tendency toward

A single-phase system that is in thermodynamic equilibrium and not subject to external forces will have particles uniformly distributed in space. But a system having concentration gradients may not be in equilibrium. The thermodynamic tendency toward equilibrium is a tendency toward uniform concentrations. 

Most chemical reactions are exothermic. In the few endothermic reactions that are known, heat is absorbed into the reaction product or products, which are known as endothermic or energy-rich compounds. Such compounds are thermodynamically unstable because heat woiild be released on decomposition of their elements. The majority of endothermic compounds possess a tendency toward insta-bihty and possibly explosive decomposition under various circumstances of initiation. 

Calculations of the nucleophilic reactions with MeO" were performed for the carbocations 4H+, 5H+ and 6H+ in order to simulate the crucial step of aza-PAH/adduct formation. These reactions were considered as models for evaluation of the reactivity trend for these carbocations toward nucleophiles. Thus, the thermodynamical tendency of each carbocation to react with the nucleophilic sites of DNA was estimated. 

Heterocycles with conjugated jr-systems have a propensity to react by substitution, similarly to saturated hydrocarbons, rather than by addition, which is characteristic of most unsaturated hydrocarbons. This reflects the strong tendency to return to the initial electronic structure after a reaction. Electrophilic substitutions of heteroaromatic systems are the most common qualitative expression of their aromaticity. However, the presence of one or more electronegative heteroatoms disturbs the symmetry of aromatic rings pyridine-like heteroatoms (=N—, =N+R—, =0+—, and =S+—) decrease the availability of jr-electrons and the tendency toward electrophilic substitution, allowing for addition and/or nucleophilic substitution in yr-deficient heteroatoms , as classified by Albert.63 By contrast, pyrrole-like heteroatoms (—NR—, —O—, and — S—) in the jr-excessive heteroatoms induce the tendency toward electrophilic substitution (see Scheme 19). The quantitative expression of aromaticity in terms of chemical reactivity is difficult and is especially complicated by the interplay of thermodynamic and kinetic factors. Nevertheless, a number of chemical techniques have been applied which are discussed elsewhere.66... 

When a steady state condition has been achieved. Equation 21 implies that the relative surface concentrations are only functions of the bulk concentrations and the sputtering coefficients. This point cannot be overemphasized. Many authors have misinterpreted their data because they did not understand the consequences of this result. Once the sputtering coefficients are known, then thermodynamic properties, such as a tendency towards surface segregation, do not affect the surface concentration. However, the sputtering yields themselves are partially determined by binding energies and the type of compounds which are present in the surface region. These parameters are, of course, influenced by thermodynamic considerations. 

For purposes of illustration in what follows, we consider the cases of various specific biopolymer mixtures demonstrating the roles of different thermodynamic parameters in determining the tendency towards phase separation. The deciding role of a greater positive value of Ay is indicated for mixtures in which there is a small difference in thermodynamic affinities of the two biopolymers for the solvent, AA2 = A - Au. A pair... 

Finally, we note here that the dehydration of biopolymers associated with their attractive non-ionic interactions (dipole-dipole, hydrophobic) can increase the contribution of the mixing entropy. This in turn can lead to a tendency towards enhancement of the thermodynamically favourable interactions between them (Appelqvist and Debet, 1997 Cai and Arnt-field, 1997 Semenova a/., 1991b). 

In general, the greater the thermodynamic stability of the imine complex, the smaller the tendency towards hydrolysis. The hydrolysis of the imine formed from aniline and benz-aldehyde is enhanced 100,000 times in the presence of copper(n). The importance of the electron configuration of the metal ion is seen in the reactions of this same ligand the imine is stabilised with respect to hydrolysis on co-ordination to a d6 iron(n) centre. This may be partially ascribed to the effective back-donation from the low-spin d6 centre (Fig. 4-24). In this case, the free imine is reasonably stable to hydrolysis in the absence of metal ions. 

These ABO4 compounds, although they have high thermodynamic stability, have a pronounced tendency toward polymorphism, the rationale for which is incompletely formulated (2, 3). There is... 

The exceptional rank of water is manifested by its unusual properties compared with most other liquids, the so-called anomalies. These anomalies comprise thermodynamic as well as structural and dynamic properties, especially their pressure and temperature dependence. The key to understanding these properties lies in two competing influences on the local structure the attempt to build low-density tetrahedral structures (with low energy) versus the tendency toward closer packing (with higher entropy) (19). 

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