Solute shifts

1 Neutral solutes. Perhaps the most informative studies have been 

2 Ions. There was extensive early work on concentration shifts for alkali-metal and halide ion resonances. These are strongly dependent upon salt concentration and on the nature of the gegen ions [23]. Clearly, dehydration and ion pairing are both involved in these shifts, which tend toward the pure salt values. However, no firm structural information has been forthcoming. 

Proton resonance shifts for salts in water have been studied for many years [25,26], but have proven difficult to interpret. Apart from the other problems associated with time-averaged shifts, this arises because of the problem of assigning separate shifts to cations and anions in a non-empirical fashion. Because of its relative simplicity, we have studied methanol rather than water [27] and endeavoured to extrapolate to aqueous solutions [28]. 

Fortunately, for methanolic solutions, the first problem can be simplified by using Mg salts at low temperatures such that the band of Mg(MeOH) units is separately resolved because of slow exchange [29]. It was originally argued that shifts in the bulk MeOH resonance is then purely due to the anions [26,27]. However, this cannot be the case if the effect of changes in concentrations of and groups are also considered [30,31]. 

When this is done, a reasonably self-consistent set of results is obtained. Using shift values for and (LP), units taken from infrared correlations, a 

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The potassium chloride precipitates from the solution shifting the equilibrium to the right side. On heating to 100 °C this NaaSs sample decomposed exothermically to a 1 1 mixture of NaaSa and Na2S4 similar to the one described above. 

If one of two equilibrating diastereomers crystallizes out of solution, shifting the equilibrium in one direction, the process is referred to as an asymmetric transformation of the second kind lUPAC Compendium of Chemical Technology, 2nd Edition, Mc-Naught, A. D., Wilkinson, A., Eds. Blackwell Science, 1997. 

Membrane uptake of nonionized solute is favored over that of ionized solute by the membrane/water partition coefficient (Kp). If Kp = 1 for a nonionized solute, membrane permeability should mirror the solute ionization curve (i.e., membrane permeability should be half the maximum value when mucosal pH equals solute pKa). When the Kp is high, membrane uptake of nonionized solute shifts the ionization equilibrium in the mucosal microclimate to replace nonionized solute removed by the membrane. As a result, solute membrane permeability (absorption rate) versus pH curves are shifted toward the right for weak acids and toward the left for weak bases (Fig. 7). 

Cyclization of 776 with ortho-esters gave (83JOC1628) [l,2,4]triazolo-[4,3-fc]pyrimido[5,4-< ][ 1,2,4]triazines 777, whereas reaction with sodium nitrite afforded the corresponding tetrazolopyrimidotriazine 778.3-Azido-pyrimido[4,5-e][l, 2,4]triazine 779 exists in a cyclic form as tetrazolo derivative 780, as shown by X-ray analysis (86KGS114). In solution the position of the 779 780 equilibrium depended on temperature and solvent. Higher temperatures favored 779. Azido compound 779 predominated in water, and tetrazolo compound 780 predominated in pyridine. Addition of sodium azide to the aqueous solution shifted the equilibrium toward 780. The... 

At the beginning stage of dehydrogenation, the substrate organic hydride is adsorbed onto the catalyst surface from the liquid phase directly and easily. Catalytic reaction processes will succeed it, until the surface sites are filled with the adsorbed reactant and products. Once product desorption starts to form and grow a bubble, product readsorption becomes unfavorable due to the increment of translational entropy of the product molecule in the bubble, if compared with that in the solution, shifting the adsorption equilibrium for the product and suppressing its effect of rate retardation. 

The addition of base (OH-) shifts the equilibrium to the left while acidification of the solution shifts the equilibrium to the right in favor of Cr20 2. In other coIor/pH relations, red CrOs is acidic, green Cr20s is amphoteric and the black CrO is basic in nature. 

Acidic and basic compounds often show more complex behavior with non-linear van t Hoff plots and with an increased retention at high temperatures in some cases. This is due primarily to the impact of temperature on the various equilibrium constants at play in the solutions [25], All equilibrium constants are temperature dependent. When the solute has multiple equilibrium forms, the retention depends on the fraction of the solute in each form, with the neutral form being more highly retained on the reverse phase HPLC column. The p/f of water is also temperature sensitive, with the pH of a neutral solution shifting to a lower pH as the temperature increases. 

Also, different metallothioneins, a group of peptides and proteins, which play an important role in metabolism of metals in living organisms, have been studied [101, 102]. In the range of more anodic potentials, cycKc voltammograms recorded in the absence of metal ions were similar to those obtained for disulfide-containing proteins. The presence of metal ions in the solution shifted the voltammetric peaks, depending on the stability of the formed complex. 

Indicators have different colors in the combined and dissociated forms. The equilibrium of the indicator in solution shifts according to Le Chatelier s principle as an acid or base is added to the solution. The shift in equilibrium to the right or left causes the color to change accordingly. 

Figure 5a also indicates that the Rb,i value corresponding to the maximum solute separation of case I solute shifts gradually to the smaller value as the h2 value decreases and ultimately disappears when... 

Photooxidation of Eosin with periodate ion has been used to initiate the polymerization of acrylonitrile in aqueous solution [187]. Addition of acrylonitrile to a periodate solution shifts the absorption maximum from 220 to 280 nm. This spectral change is interpreted as being due to complex formation between the monomer and oxidizing agent. The rate of photopolymerization increases linearly with the absorbed light intensity and monomer concentration. The observed intensity dependence indicates the main chain terminator is not produced photochemically. Polymer is not formed when the concentration of periodate ion is lower than 0.5 mM and the rate of polymerization is independent of its concentration for higher values. 

When the metal ion of an insoluble salt forms a complex ion, the aquo cation is removed from solution, shifting the solubility equilibrium toward solution species. 

The MPE study of the dielectric environment effects on the spin-spin coupling constants of acetylene [43] allowed for a comparison with experimentally measured gas-to-solution shifts for a series of solvents of varying polarity. It has been found in the experimental study that 1JCC changes considerably with the solvent, and that the changes correlate approximately with the solvent polarity. This tendency has been qualitatively reproduced by the MPE MCSCF linear response calculation, although the calculated changes constitute only approximately 30 % of the experimental shifts. 

An increase in the number of methyl substituents on the alkylidene carbon atom of the hydrazones 63 (R4 = R5 = H < R4 = H R5 = Me < R4 = R5 = Me) displaces the equilibrium in favor of the open-chain tautomer. The steric demands of the open-chain 63A and the cyclic 63B tautomers clearly differ from those in the systems 59 and 61, where an opposite effect was detected. An increase in the temperature of the solutions shifts the equilibrium toward the open-chain tautomer. In most cases, an equilibrium shift in the same direction was observed on increase of the solvent polarity (83ZOR2310). /V-(3-Aminoprophyl)-A-methylhydrazones 65 (R = H, Me) exist as stable open-chain isomers and do not exhibit any tendency to seven-membered-ring closure (83ZOR2310). 

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