Stability prediction

Apart from this simple result, comparison of stability predictions for the two limiting situations can be made only by direct numerical computation, and for this purpose a specific algebraic form must be assumed for the reaction rate function, and a specific shape for che catalyst pellet. In particular, Lee and Luss considered a spherical pellet and a first order... 

The following nuclides lie outside the band of stability. Predict whether each is most likely to undergo p decay, P"1 decay, or a decay, and identify the daughter nucleus ... 

The high stability of the compounds could thus be related to the strong interaction between a last transition metal (acting as an electron donor, Lewis base) and an early transition metal acceptor (Lewis acid). This stability prediction has been found in... 

The acyclic precursor is an oc, 3-unsaturated amido aldehyde that was condensed with iV-methylhydroxylamine to generate the nitrone ( )-48, which then underwent a spontaneous cycloaddition with the alkene to afford the 5,5-ring system of the isoxazolidinyl lactam 47. The observed product arises via the ( )-nitrone transition state A [or the (Z)-nitrone equivalent] in which the position of the benzyl group ot to the nitrone effectively controls the two adjacent stereocenters while a third stereocenter is predicted from the alkene geometry. Both transition states maintain the benzyl auxiliary in an equatorial position and thus avoid the unfavorable 1,3-diaxial interaction with the nitrone methyl or oxygen found in transition state B. Semiempirical PM3 calculations confirm the extra stability, predicting exclusive formation of the observed product 47. Related cycloadducts from the intramolecular reaction of nitrones containing ester- rather than amide-tethered alkene functionality are also known (83-85). 

Theoretically, use of fuel as a coolant is convenient. But, it is well known that heating oils for even short periods of time accelerates gum and sediment formation. (In fact, this is the basis for many stability prediction tests in the petroleum industry.) It was not unexpected then, that when fuels are heated in aircraft fuel systems, temperatures would be high enough to cause some fuel degradation... 

Table I. Comparison of Coko Oven Stabilities Predicted from Highly Oxidized Coals on an As-Received and Corrected Basis...

The following nuclides lie outside the band of stability. Predict whether they are most likely to... 

When the more than 3600 known nuclides are plotted on the neutron/proton grid in Figure 22.3, they fall in a curved band sometimes called the "band of nuclear stability." Even within the band, only 264 of the nuclides are stable indefinitely. The remainder decay spontaneously, although their rates of decay vary enormously. On either side of the band is a "sea of instability" representing the large number of unstable neutron/proton combinations that have never been seen. Particularly interesting is the "island of stability" predicted to exist for a few superheavy nuclides near 114 protons and 184 neutrons. The first members of this group—287114,288114,289114, and 292116—were prepared in 1999 and do indeed seem to be unusually stable. Isotope 289114, for example, has a half-life of 30.4 seconds. 

Furlanetto S, Mura P, Gratteri P, Pinzauti S. Stability prediction of cefazolin sodium and cephaloridine in solid state. Drug Dev Ind Pharm 1994 20 2299-2313. 

Monkhouse D. Excipient compatibility possibilities and limitations in stability prediction. Paperback APY, 1993. 32 (Stability Testing in the EC, Japan and the USA) 67-74. 

The stability of BHs (and conjugated systems in general) is usually appraised through the topological resonance energy per electron, TRE(PE), [31]. Unfortunately, though we cannot deny that the concept of TRE has a certain elegance and simplicity, there are numerous examples of the stability predictions based on TRE that are contrary to the chemical sense. In particular, molecules with unpaired electrons (radicals) are predicted to be excessively stable within the TRE approach [32]. 

S. Furlanetto, P. Mura, P. Gratteri, and S. Pinzauti, Stability predictions of cefazolin sodium and cephaloridine on solid state, Drug Dev. Ind. Pharm., 20 2299 (1994). 

Write equations for the following acid-base reactions. Label the conjugate acids and bases, and show any resonance stabilization. Predict whether the equilibrium favors the reactants or products. If in doubt, you can consult Appendix 4 for acids not shown in Table 1-5. 

In addition to the steric and electrostatic descriptors, it was proposed to use other 3D molecular fields characterized by the sampling over the rectangular grid - in particular, the hydrophobic field/molecular lipophilic potential (MLP), ° hydrogen bonding and quantum-chemical parameters, e.g., orbital densities.Descriptor selection techniques are often recommended to enhance the stability, predictivity and interpretability of the CoMFA models. ... 

As shown before, it takes a quantitative method of complex stability prediction rather than some qualitative argument like HSAB (Pearson) or A/B patterns (Ahrland et al.) to give sense to the observed relationships among substrates/products and (biocatalytic) metal ions. It must thus be feasible to derive binding properties to a given metal ion directly from properties of substrates and products. Metals tend to be coordinated rather stably to plant... 

It should be understood that since the stability predictions involve reaction-rate properties, planar Chapman-Jouguet detonations are stable for suitable rate functions. For example, if the rate of heat release decreases monotonically with an increasing extent of reaction behind the shock, then the mechanism for the instability is absent. The failure to find Chapman-Jouguet detonations without transverse structures reflects the inability to encounter real chemical systems with reaction-rate properties suitable for stability. 

The last row of Table 2.3 reveals the profound difficulties in using the 6-311G basis set where the triple split of the valence set might normally be expected to be an improvement over 6-3IG. Instead, the SCF BSSE is more than doubled, and an increase of similar magnitude occurs in the correlated superposition error. Indeed, the correlation component is completely distorted by superposition effects Essentially all the (1.93 kcal/mol) stabilization predicted by MP2 with this basis set is due to the artifact of superposition. Removal of this error leaves only a net stabilization of less than 0.1 kcal/mol. 

Unfortunately, it is expected that the chemistry of these elements will not be able to be studied because the theoretical investigations of nuclear stability predict that these elements will be unstable and have very short hfetimes. Before this was known, a large number of theoretical calculations of the ground-state electronic configurations were made in this region because the proton number Z = 126 was long expected to be the center of the first island of stability. Now this is considered unhkely. Nevertheless, the chemistry of these elements would be very interesting. 

The same residence time of 195 seconds which fits the fibril stabihty versus M data for PS also can be used to predict the fibril stability in the blends of high and low molecular weight PS. The computed fibril stability for these blends is shown as the solid curve in Fig. 36. The general decrease in fibril stability predicted as the volume fraction of high molecular weight PS in the blend is decreased is in reasonable agreement with the data. 

The thiazolidine structures in the dihydrothiazolyl hydrazones 53a and 54a were confirmed both by crystallography and in solution by NMR. The stability of the endocyclic N-3 (N-3/N-6 tautomerism) tautomeric forms 53b and 54b, in the gas phase and in water, were confirmed by energy calculations at the MP2/6-31- -G(d) level. These tautomeric structures are expected to be the most abundant form (>90%) of the molecule. The <7 A- -conformations observed in the crystal structures were retained in solution in agreement with stability predictions (Scheme 3) <2002J(P2)1012>. 

Chemical stability predictions are sometimes complicated by the difficulty of determining the pH value of suspensions, which often changes because of surface coating of electrodes and differences between bulk-suspension and supernatant-vehicle readings. Accelerated elevated temperature stability testing often has a pronounced adverse effect on viscosity, particle solubility, and size distribution. 

FSSF is isomeric with SSF (3). Qualitative evidence has been presented (1 ) which indicates that SSFg is the more stable isomer. From our estimated free energy data, we predict a Gibbs energy change for the isomerization reaction FSSF(g) = SSF (g) of -15.4 kcal mol at 298.15 K, indicating that SSF is substantially more stable than FSSF. This conflicts with relative stability predictions based on results from two Independent MO studies (5, 6). These semiempirical (CNDO/2) calculations indicate that the instability of FSSF relative to SSF amounts to only about 2.0 kcal mol". If we assume that these MO calculations are correct, we calculate that Dq (FS-SF) > Dq (S=SF2) by roughly 7.0 kcal mol". This seems very unlikely in view of what is known (1 ) about the... 

M. A. Zoglio, H. V. Maudling, W. H. Streng and W. C. Vincek. Nonisothermal kinetic studies III rapid nonisothermal-isothermal method for stability prediction. /. Pharm. Sci., 64, 1381 (1975)... 

To ensure better stability predictions, an understanding of the limitations of experimentally obtained heat of activation values is critical. For instance,... 

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