From Proton-Magnetic-Resonance Measurements

Less direct evidence for the position of the H atom also comes from proton magnetic resonance studies and from values of residual entropy. The positions of the protons in the H2O molecules in gypsum have been determined indirectly from the fine structure of the n.m.r, lines they are found to lie at a distance of 0-98 A from the 0 atom along an O-H-0 bond. For n.m.r. studies of a number of hydrates see p. 564 the method has also been used to locate the H atoms in Mg(0H)2 (p. 521). Measurements of residual entropy confirm the existence of two distinct locations for the proton in hydrogen bonds in ice (p. 539), salts of the type of KH2PO4, and Na2S04.10 H2O (which has residual entropy about two-tenths that of ice). 

This effect is probably due to the structure of water in the gel, which is most probably different from the water structure within the coil. According to proton magnetic resonance measurements, the water within the gel in poly(styrene sulfonic acid) is less ordered than that outside the gel. Since the degree of order varies with the density of cross-linking, this discovery could also explain why the selectivity of an ionized gel with respect to ions goes through a maximum with increasing cross-link density. 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

Infrared measurements show that cefalori-dine exists in a, 6, e, and y. forms (that is, six forms after recrystallisation from different solvents). Proton magnetic resonance... 

Structural assignments have been made for each peak in the proton magnetic resonance spectrum of sodium phenoxymethyl penicillin (fourth line of Table 5 in reference 5) by Green and co-workers. Proton resonance lines were measured in D2O solution at 38°,with either t-butyl alcohol or sodium 3-(trimethylsilyl) propane-l-sulfonate (assumed to be 2 cycles per second below Me Si) as the internal standard, with the results referred to tetramethylsilane (Me4Si=10.Ot). Cohen and Puar made structural assignments for the peaks of potassium phenoxymethyl penicillin measured in D2O solution at 33° with the results referred to tetramethylsilane as the external standard (Me Si O. Ot). Figure 2 is the spectrum of the Squibb Primary Reference Substance from which proton assignments were made . Spectra in both laboratories were measured on Varian A-60 spectrophotometers. 

It was possible to rationalize the family of Arrhenius plots measured for Nafion 117 at different water contents [46]. Under an assumption that the surface conductivity has higher activation energy, supported by microscopic considerations in Refs. 40, 43, the Arrhenius slope should become steeper with the decreasing amount of water in the membrane [39], that is, the smaller the amount of the bulk water that we have in pores. Activation energies obtained from these plots are 0.1 eV for the largest possible water contents (Activation energies of proton transfer in water, estimated from nuclear magnetic resonance relaxation times, are 0.1 eV [47].) and 0.3-0.4eV at small water contents. How to rationalize this variation. ... 

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