Constant tentative

Oxygen + water. Battino s recommended four constant equation from an earlier work (5 ) was used to represent the low temperature (273-348 K) mole fraction oxygen solubility values. The data determined at the Battelle Memorial Institute laboratories in the early 1950 s (10,12) were used to estimate the one atmosphere oxygen pressure solubilities at higher temperatures. The data sets were combined in a linear regression to obtain the parameters of the three constant tentative equation for the solubility between 350 and 600 K (Table V, Figure 9). 

Fig. 28.16. Tentative design for o self-sprung wheel. The spokes and the rim both deflect. The design ensures that the sum of the deflections is constant.

Dependence of apparent constants on concentration. We continue the consideration of Scheme XXIII by making chemically reasonable tentative selections of the forms of A a and k[. First, consider the acetyl chloride-alcohol reaction. Because the spectral observations show that intermediate formation is essentially complete, this system belongs to the case in which kdk i may be treated as infinite (Scheme XXIV). The observed reaction is then... 

Attempts have been made to deduce the structure of the predominant form of a potentially tautomeric compound from the shifts which occur in the ultraviolet spectrum of the compound in question on passing from neutral to basic or acidic solutions. The fact that no bathochromic shifts were observed for 2- and 4-hydroxy quinoline and 1-hydroxyisoquinoline under these conditions was taken as evidence that they existed in the oxo form [similar work on substituted quinol-4-ones led to no definite conclusions ]. A knowledge of the dissociation constants is essential to studies of this type, and the conclusions can, in any case, be only very tentative. A further dif-... 

Recently, many investigators have extended the early observations that the ultraviolet spectra of - and y-hydroxypyridines resemble those of their A -methyl (not the 0-methyl) derivatives. This spectral resemblance is found both in aqueous solutions and in solutions of solvents with low dielectric constants, e.g., quinol-4-one in benzene, indicating that these compounds exist predominantly in the oxo form under all conditions. These data are summarized in Table I. In contrast, 4-hydroxyquinoline-3-carboxylic acid has been tentatively concluded to exist in the hydroxy form %- pjTid-2-one-4-carboxylic acid has also been formulated as a hydroxy compound, but this has been disputed. ... 

In recent years various attempts have been made to account for the observed differences between the dissociation constants of organic acids, whose molecules differ only slightly from each other. The proposed explanations have naturally been given in each case in terms of the structures of the respective neutral acid molecules.1 In the tentative discussion of HN03 and HI03 that has just been given, the approach has been quite different we focused attention, not on the neutral molecule or on the structure of the anion, but on the condition of the solvent in the vicinity of the anion. 

The values of i calculated from (8) and (8) do not agree very closely, and it would appear, as Weinstein (loc. cit. 1068) remarks, that Although the calculations undoubtedly establish the legitimacy of the system of equations, the great uncertainty in the numerical determination of the decisive magnitudes forms a practical defect which will only be removed by observations over very wide intervals of the variables. Any discrepancy between the results of actual observations of equilibria, and those calculated by means of Nernst s chemical constants, need not, in the present state of uncertainty of the latter, cause any great alarm. Nernst himself apparently regards the constant < >, obtained from vapour-pressure measurements, as the most certain, and the others as more or less tentative. 

However, an evaluation of the observed (overall) rate constants as a function of the water concentration (5 to 25 % in acetonitrile) does not yield constant values for ki and k2/k i. This result can be tentatively explained as due to changes in the water structure. Arnett et al. (1977) have found that bulk water has an H-bond acceptor capacity towards pyridinium ions about twice that of monomeric water and twice as strong an H-bond donor property towards pyridines. In the present case this should lead to an increase in the N — H stretching frequency in the o-complex (H-acceptor effect) and possibly to increased stabilization of the incipient triazene compound (H-donor effect). Water reduces the ion pairing of the diazonium salt and therefore increases its reactivity (Penton and Zollinger, 1971 Hashida et al., 1974 Juri and Bartsch, 1980), resulting in an increase in the rate of formation of the o-complex (ik ). 

The unexpected dependence of the rate constant on the reactant concentration was tentatively assigned to traces of... 

Tentative values of a reaction order, x, and rate constant, k, for the proposed distillation reaction can be calculated from the data in Table V using Equation 23 and the relationship... 

In nitrate and sulfate media, Cr(III) is not very stable and the reaction Cr(II) -> Cr tends to be irreversible. The rate constants obtained in these media are tentative because of excessive adsorption of chromous ions in these media. The rate constants have been... 

For frequency calculations one usually starts out with a set of approximate existent force constants (e.g. taken over from similar, already treated molecules under the preliminary tentative assumption of transferability), and subsequently varies the force constants in a systematic way by means of a least-squares procedure until the calculated frequencies (square roots of the eigenvalues of Eq. (10)) agree satisfactorily with the experimental values. Clearly, if necessary, the analytical form of the force field is also to be modified in the course of this fitting process. 

The electrochemical behavior of niclosamide was described on the basis of d.c. polarography, cyclic voltammetry, a.c. polarography, and differential pulse polar-ography, in the supported electrolytes of pH ranging from 2.0 to 12.0 [32], A tentative mechanism for the reduction of niclosamide is proposed that involves the transfer of 4 e . Parameters such as diffusion coefficients and heterogeneous forward rate constant values were evaluated. 

For the reasons we have just been discussing, we shall focus attention on the uptake of hydrogen by samples hydrogenated by exposure to plasma products for times of the order of an hour at 300°C and shall analyze the data on the assumption that the surface chemical potential / for given external and surface conditions is roughly independent of donor or acceptor doping. However, our conclusions will be tentative, since presently available data are limited and both the assumption of local equilibration and that of constant surface p need further checking. 

The initial rate is given by the numerical value of m1 from polynomial fitting. The rate proved to be a function of three concentration variables, [1], [PyO] and [PPh3]. Values of the rate were determined in series with two variables maintained constant and the third varied. This led to this tentative rate equation ... 

This expresses tR as a function of the fundamental column parameters t0 and k tR can vary between t0 (for k = 0) and any larger value (for k > 0). Since to varies inversely with solvent velocity u, so does tR. For a given column, mobile phase, temperature, and sample component X, k is normally constant for sufficiently small samples. Thus, tR is defined for a given compound X by the chromatographic system, and tR can be used to identify a compound tentatively by comparison with a tR value of a known compound. 

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