Observed activity

Similar difficulties arise in the nitrations of 2-chloro-4-nitroaniline and /)-nitroaniline. Consideration of the rate profiles and orientation of nitration ( 8.2.5) these compounds suggests that nitration involves the free bases. However, the concentrations of the latter are so small as to imply that if they are involved reaction between the amines and the nitronium ion must occur upon encounter that being so, the observed activation energies appear to be too high. The activation energy for the simple nitration of the free base in the case of/>-nitroaniline was calculated from the following equation ... 

Theoretical treatment of the reaction as a conrotatory process proceeding through the very unstable Z,Z, -isomer of benzene satisfactorily accounts for the observed activation barrier. ... 

TABLE I.a Comparison of Observed Activity Coefficients of Cu and Au with Values Calculated from Observed Short-Range Order Parameters by the First-Order Quasi-Chemical Theory... 

The mathematical model was found to describe well the observed activity increase for numerous mechanical mixtures of a-Sb204/Mo03 at different oxygen partial pressures and temperatures.73... 

Doors present certain hazards, too, since a collision is likely to take place when two people approach a door from opposite directions at the same time. Even a small window in every door makes it possible to observe activities on the other side and prevent such problems. This may not be possible in those few cases where fire resistant doors are called for. 

Because of the fact that the NO conversion on AljO, increases faster than linearly with sample weight, the contribution of AI2O3 to the observed activity of AU/AI2O3 increases when a larger amount of catalyst is used, and at higher temperatures. When 0.1 g of catalyst is used, the data in Tables 2 and 3 show that A1,0, does not contribute much to the observed NO reduction... 

Although a few mechanisms have so far been proposed to explain the antimicrobial properties exhibited by proanthocyanidins (e.g., inhibition of extracellular enzymes) [86], Jones et al. [83] postulated that their ability to bind bacterial cell coat polymers and their abihty to inhibit cell-associated proteolysis might be considered responsible for the observed activity (Table 1). Accordingly, despite the formation of complexes with cell coat polymers, proanthocyanidins penetrated to the cell wall in sufficient concentration to react with one or more ultra-structural components and to selectively inhibit cell wall synthesis. Decreased proteolysis in these strains may also reflect a reduction of the export of proteases from the cell in the presence of proanthocyanidins [83]. 

Analogously to external mass transfer, internal mass transfer can be the rate-limiting step. In that case, it appears that the observed activation energy is related to the true activation energy as follows ... 

It has been shown that PLS regression fits better to the observed activities than principal components regression [53]. The method is non-iterative and, hence, is relatively fast, even in the case of very large matrices. 

In the case of radioactive materials contained in living organisms, an additional consideration is made for the reduction in observed activity due to regular processes of elimination of the respective chemical or biochemical substance from the organism. This introduces a rate constant called the biological half-life (Tbioi) which is the time required for biological processes to eliminate one-half of the activity. This time is virtually the same for both stable and radioactive isotopes of any given element. 

Jenner investigated the kinetic pressure effect on some specific Michael and Henry reactions and found that the observed activation volumes of the Michael reaction between nitromethane and methyl vinyl ketone are largely dependent on the magnitude of the electrostriction effect, which is highest in the lanthanide-catalyzed reaction and lowest in the base-catalyzed version. In the latter case, the reverse reaction is insensitive to pressure.52 Recently, Kobayashi and co-workers reported a highly efficient Lewis-acid-catalyzed asymmetric Michael addition in water.53 A variety of unsaturated carbonyl derivatives gave selective Michael additions with a-nitrocycloalkanones in water, at room temperature without any added catalyst or in a very dilute aqueous solution of potassium carbonate (Eq. 10.24).54... 

Usually the last term on the right side of equation 4.3.10 is only a very small fraction of the total. For example, if the observed activation energy (Ea) is 10 kcal at 500°K, the RT/2 term is only 0.5 kcal or 5%. Such discrepancies are usually within the scatter of the data. 

It was claimed that this model helps to explain earlier catalytic results using Cu-Ni alloys, but comparisons with alloys in granular, or other massive form, are difficult. The available catalytic results on Cu-Ni alloys show that the method of preparation of the catalyst can have a profound influence upon the observed activity pattern. The promoting effect on the catalytic activity, caused by cooling in hydrogen rather than in vacuum... 

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