Stability relationships

For the 2223 compound of the Tl-Ba-Ca-Cu-0 compound the loss of thallium is reduced by surrounding a pre-fired, and thallium-deficient, sample with powder of the compound and refiring. These substances also show a temperature-oxygen partial pressure stability relationship, similar to the classical 123 compound, but the details have not yet been elucidated. 

Some fundamental structure-stability relationships can be employed to illustrate the use of resonance concepts. The allyl cation is known to be a particularly stable carbocation. This stability can be understood by recognizing that the positive charge is delocalized between two carbon atoms, as represented by the two equivalent resonance structures. The delocalization imposes a structural requirement. The p orbitals on the three contiguous carbon atoms must all be aligned in the same direction to permit electron delocalization. As a result, there is an energy barrier to rotation about the carbon-carbon... 

One of the most important and general trends in organic chemistry is the increase in carbocation stability with additional alkyl substitution. This stability relationship is fundamental to imderstanding many aspects of reactivity, especially of nucleophilic... 

Because these stability measurements pertain to the gas phase, it is important to consider the effects that solvation might have on the structure-stability relationships. Hydride affinity values based on solution measurements can be derived from thermodynamic cycles that relate hydrocarbon p T, bond dissociation energy and electrochemical potentials. The hydride affinity, AG, for the reaction... 

Provide an explanation for the relative reactivity or stability relationships revealed by the following sets of data. 

Stability relationships among analogous molecular addition compounds of group III elements. 

Y. Mozhaev, I. Berezin, and K. Martinek, Structure stability relationship in proteins Fundamental tasks and strategies for the development of stabilized enzyme catalysts for biotechnology, CRC Crit. Rev. Biochem., 23, 235 (1988). 

Among the oxyacids of sulfur the predilection to form an anhydride with a sulfur-sulfur bond, rather than one with an oxygen bridge between the two sulfurs, is not restricted to sulfenic acids. We will see in a subsequent section that sulfinic acids also do this. Their anhydrides have the sulfinyl sulfone structure. RS(0)S02R, rather than RS(0)0S(0)R. What is unique about the sulfenic acid-thiolsulfinate system, however, is the fact that the anhydride (thiolsulfinate) is strongly preferred thermodynamically over the acid at equilibrium. With any other type of common acid the reverse is true, of course. The uniqueness of the sulfenic acid-thiolsulfinate situation can perhaps best be appreciated by realizing that, if the same stability relationship between acid and anhydride were to exist for carboxylic acids, acetic acid would spontaneously dehydrate to acetic anhydride ... 

A comprehensive review covers stability relationships and reactions of these explosive compounds and their derivatives. Bromine, chlorine and iodine azides all explode violently in contact with magnesium, zinc or white phosphorus. 

V. H. Naringrekar, V. J. Stella, Mechanism of Hydrolysis and Structure-Stability Relationship of Enaminones as Potential Prodrugs of Model Primary Amines , J. Pharm. Sci. 1990, 79, 138 - 146. 

In conjugated molecules one or other of the possible protonation sites may be more or less favoured by solvation effects and for this reason sites of protonation are often solvent dependent. In some instances, similar stability of two possible cations results in tautomeric equilibria and these too may be solvent dependent. Just as solute-solvent interactions have an effect on the relative stability of two possible cations formed from a conjugated molecule, so in solid salts stability relationships depend on the mode of packing of ions, which determines interactions with the nearest neighbours. Therefore the types of cation observed in solid salts are not necessarily the most stable ones in solution. 

Let us examine in detail the phase stability relationships of the four end-members of the pyroxene quadrilateral. Figure 5.24A shows the P and T stability ranges of the various polymorphs of the Mg2Si206 compound, according to Lindsley (1982). The stable form... 

Mozhaev, V.V. and Martinek, K. (1984) Stmcture-stability relationships in proteins new approaches to stabilizing enzymes. Enzyme Microb. Technol., 6, 50-59. 

De Diego, T., Lozano, R, Gmouh, S., Vaultier, M., Iborra, J.L., Understanding structure-stability relationships of Candida antartica lipase B in ionic liquids, Biomacromol., 6,1457-1464, 2005. 

In addition to the three principal polymorphs of silica, three high pressure phases have been prepared keatite [17679-64-0], coesite, and stishovite. The pressure—temperature diagram in Figure 5 shows the approximate stability relationships of coesite, quartz, tridymite, and cristobalite. A number of other phases, eg, silica O, silica X, silicalite, and a cubic form derived from the mineral melanophlogite, have been identified (9), along with a structurally unique fibrous form, silica W. 

The section on crystallization comprises zeolite synthesis, kinetics and mechanism of formation, stability relationships, recrystallization processes as well as the genesis of natural zeolites. Recent advances in this field have been surveyed, and some new perspectives have been outlined in the review by E. M. Flanigen. Most of the studies in this field are still empirical because of the complexity of the systems involved. Considerable progress has been made, however, towards a better understanding of the processes and mechanisms governing zeolite crystallization. It is not unreasonable to expect that conditions for synthesizing new zeolite structure types can eventually be predicted. 

Hay, B.P. Rustad, J.R. Hostetler, C.J. Quantitative structure-stability relationship for potassium ion complexation by crown ethers. A molecular mechanics and ab initio study. J. Am. Chem. Soc. 1993, 115 (24), 11158-11164. 

The staring point is the baseline state of consciousness(b-SoC), usually the ordinary d-SoC. The b-SoC is an active, stable, overall patterning of psychological functions which, via multiple stabilization relationships (loading, positive and negative feedback, and limiting) among its constituent parts, maintains it identity in... 

Some very important features of thermal aging cannot be easily understood without a kinetic reasoning. In the following section, a simple kinetic model is postulated, which, in spite of its oversimplification, allows us to understand most of the general properties of thermal aging. The structure-thermal stability relationships are briefly examined and then some practical aspects are presented. 

From the above examples it is apparent that a pertinent classification of thermal stabilities is not obvious. however, some clear structure-stability relationships can be derived from experimental results. The most important characteristic to be found is the mechanism by which thermal aging proceeds a chain process or a step process. The most unstable polymers are those that undergo degradation chain processes, for example ... 

Structural and compositional characterization of individual elements of a combinatorial library can be important for the initial validation of a particular combinatorial synthesis method. Many earlier reports on combinatorial synthesis and screening of electrocatalysts fall short of reporting the complete structural and compositional characterization of individual library elements of interest. The workflow described here includes catalyst characterization before and after screening, thereby establishing an activity-composition-structure-stability relationship for electrocatalysts. This can be relevant in light of the extreme conditions present in a conventional fuel cell environment. 

Martell, A. E., R. J. Motekaitis, and R. M. Smith. 1988. Structure stability relationships of metal complexes and metal speciation in environmental aqueous solutions. Environmental Toxicology and Chemistry 7 417—434. 

Entering adulthood Experimenting with different job settings, stabilizing relationships, and possibly starting a family... 

In many cases the most important aspect of structural studies is that knowledge of the structure of a protein leads to improved understanding of its function. For instance, if a protein has to be administered for lifetime or long-firm TAnjswmnii therapy (c.g, insulin, growth hormone, factor IX), it is import tant to know all about its stmcture-function-stability relationships. A longer turnover time or a higher specific activity, for example, allows for a smaller dose to... 

Stone, F. G. A. Stability Relationships among Adducts of Group III Elements, Chem. Revs., 58, 101 (1958). 

Example 3.4 Investigation of the stability relationship between gibbsite and kaolinite in natural waters at pH <7. 

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