Constant proton-dependent

FIGURE 13.18 The appearance of the splitting pattern of two coupled protons depends on their coupling constant J and the chemical shift difference Av between them. As the ratio Av/J decreases, the doublets become increasingly distorted. When the two protons have the same chemical shift, no splitting is observed. 

The observation that the macroscopic proton coefficient is a function of adsorption density and pH has several implications for macroscopic modeling of cation and anion adsorption. The dependency of x on pH and T affects 1) the relationship of the macroscopic partitioning coefficient to pH and adsorption density, 2) the notion of metal ion preferences for a particular surface in systems with multiple solid phases, 3) the accuracy of predictive models when used over a range of adsorption density and pH values, and 4) conclusions about site heterogeneity based upon partitioning expressions which use constant proton coefficients. 

Organophosphorus compounds rarely have more than one P atom in the molecule, giving rise to a doublet for any C atom within three bonds (assuming the proton-carbon coupling has been removed) and so these compounds show clearly the connectivity of carbon atoms close to the P atom. The size of the coupling constant is dependent on the number of bonds and the phosphorus oxidation state, such that Vis the largest at about 45-150 Hz, while V and V are of the order of 10-15 Hz. 

Acidity constants always compare the acidity of a proton donator with the basicity of the solvent. Therefore, only acidity constants relating to the same solvent can be compared [iii, iv]. The acidity constant strongly depends on the dielectric constant of the solvent and solvent-solute interaction parameters. About relations between the acidity constants of one acid in different solvents see reference [v]. 

Geminal proton—proton coupling constants (2J) depend markedly on substituents, as indicated in Table 5.1. The trend of 2J with substitution has been treated successfully by theory and will be discussed in Section 5.3. 

Most of the alcohol radicals have hyperfine coupling constants slightly dependent on both temperatures and solvents. Ayscough and McClung (220) have also studied in detail the effect of temperature variation on proton hyperfine splitting of the biacetyl semidione radical in the range 250-400 K. Livingston and Zeldes (156) observed... 

One method of circumventing this problem is the spectrophotometric measurement of competition for the metal by another thermodynamically well-characterized hgand, typically EDTA. To convert the resultant proton-dependent equilibrium constant into the conventional formation constant, it is necessary to know the hgand protonation constants. ... 

Protonation becomes a rapid reaction in protic solvents and in the presence of acids, as demonstrated for, e.g., -butyl acrylate in aqueous solution [207], methyl acrylate in EtOH [208], cinnamates in the presence of phenol in DMF [209], and benzaldehyde in ethanolic buffer solution [210]. Rate constants for protonation of aromatic radical anions (anthracene [211], naphthalene, 2-methoxynaphthalene, 2,3-dimethoxynaphthalene) by a number of proton donors including phenols, acetic acid, and benzoic acids in aprotic DMF were found to vary from 5.0 X 10 M- s-> (for anthracene, in the presence of p-chlorophenol) to 6.2 x lO s (for anthracene, in the presence of pentachlorophenol) [212]. For dimedone, PhOH, or PhC02H the rate of protonation depends on the hydrogen-bond basicity of the solvent and increases in the order DMSO < DMF MeCN [213],... 

I. Tvaroska and F. R. Taravel, One-bond carbon-proton coupling constants Angular dependence in a-linked oligosaccharides, Carbohydr. Res., 221 (1991) 83-94. 

Under our experimental conditions, the overall rate constant of the photochemical reductive dissolution of lepidocrocite in the presence of oxalate is pH-dependent. Thus, the pH dependence of the rate reflects more than the pH dependence of oxalate adsorption at the lepidocrocite surface. Various pH effects may account for this observed pH dependence of ka. One possibility is catalysis of detachment of the reduced surface iron centers by protonation of their neighboring hydroxo and oxo groups. The following question then arises How does the observed rate constant, ka, depend on surface protonation The general rate expression of the proton-catalyzed dissolution of oxide... 

Due to the covalent nature of chemical bonding, properties of zeolitic protons depend on local electronic structure details. This is illustrated in Fig. 10 [105]. Using a basis set that predicts the NMR quadrupole coupling constants (QCC), accurately measured QCCs in zeolite ZMS-5 for Al tetrahedra in the proton form and deprotonated Al tetrahedra (e.g., by cation exchange) are compared with predicted QCCs from cluster model calculations. One... 

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