129Xe NMR spectra of xenon adsorbed in Na-Y, K-Y, Mg-Y, Ca-Y, and B-Y zeolites have been measured as a function of the xenon loading at 144 and 293 K. At low xenon loadings, the 129Xe chemical shift shows two types of dependence on the xenon density in the supercage: linearly increasing and paraboliclike with a minimum. At 144 K, all the zeolites except Ca-Y have a linear dependence, whereas at 293 K, both Ca-Y and Mg-Y show a paraboliclike curvature. These dependences can be explained in terms of rapid exchange between xenon atoms adsorbed at special sites in the supercage and those remaining in the gas phase in the cages. Strong xenon adsorption at the special sites leads to the paraboliclike behavior, whereas weak adsorption yields the linear dependence. Formation of a partial bond between the xenon atom and 2+ cation by donation of one of the xenon 5p electrons to the empty s-orbital of the cation is proposed to explain the strong xenon adsorption in zeolites with 2+ cations. The bond formation introduces low-lying electronic excited states which lead to a large paramagnetic contribution to the chemical shift. By variation of the rate by which a sample is cooled to 144 K, it is shown that there is only one special adsorption site per supercage in the Y zeolites. In Na-Y, Mg-Y, and K-Y, the site can accommodate one xenon atom while in Ca-Y and Ba-Y, two xenon atoms can share the same site. At 144 K, a gas-liquid phase transition is observed when the xenon loading is between 7 and 9 xenon atoms/cage. The transition is characterized by rapid increase in the chemical shift and collapse of the line width. Before the transition, there are large increases in the line width that may be interpreted as the inhomogeneous broadening due to large fluctuations in the xenon number density in the cages. Measurements at 144 K with high loadings of xenon indicate that the supercage in Y zeolite can hold between 10 and 11 xenon atoms. The resulting chemical shift is between 250 and 270 ppm downfield from the resonance of 2 atm of xenon gas (at 293 K). At even higher xenon loading, the excess xenon condenses on the exterior surface of the zeolite microcrystallites to form solid xenon, which has a chemical shift of 304 ppm downfield.

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Powder x-ray diffraction has been the most common method for rapid structural analysis and identification of crystalline ceramic raw materials.However, new structural ceramic raw materials often have linebroadened or featureless XRD patterns due to structural strain or small crystallite size. Characterization of various silicon carbide and silicon nitride powders and ceramic fibers by Si-29 NMR-MAS spectroscopy has revealed structural details and differences in these materials previously indistinguishable by XRD or other routine methods.Unique variables intrinsic to a given ceramic synthesis process are reflected in the NMR-MAS spectra of the resulting products.

SynopsisA high-temperature, high-resolution I3C nuclear magnetic resonance spectroscopy technique was developed for the analysis of poly(p-phenylene sulfide) (HT/HR NMR of PPS). This technique can be applied to the identification and quantitative analysis of end groups and polymer structure in high-temperature polymers where solution temperatures above 2OOOC are required for analysis. Verification of calculated 13C NMR shift values of chloro-terminated and hydrogen-terminated end groups was made by HT/HR NMR of two oligo(p-phenylene sulfide) model compounds.Identification of the chlorine end group was made in high-molecular weight PPS. On the highmolecular weight PPS, identification and quantitative analysis of amino and N-alkylamino end groups were possible only after derivatization of the polymer with I3C-enriched benzoyl chloride.

3193temperature of 35 "C. The reactions were monitored by ' H NMR.In case of CD30D, the integral of the methanol peak was corrected for the small amount of CHDzOD (quintet) which is always observed in this solvent.The methine (OCH) resonances of the cyclic compounds were found at about 5.1 ppm, whereas methine peaks around 4.4 ppm were attributed to ring-opened products. 'H NMR data for the methoxy resonances of the various products are as follows. In CDSOD 5 , 3.81 (d), J = 12 Hz), 3.82 (d, J = 12 Hz, 2 isomers); 6, 3.73 (d, J = 11 Hz); CH30D, 3.36 (8). In DzO: 5, 3.86 (d, J = 12 Hz), 3.87 (d, J = 12 Hz); 9,3.67 (d, J = 11 Hz); CH,OD, 3.42The proton and carbon-13 magnetic resonance spectra of 5-thio-D-glucopyranose have been fully analyzed.This molecule differs from &glucopyranose in replacement of the ring oxygen by sulfur. The ' H spectrum showed the presence of two anomers, with an a/j3 ratio of 85/15. Analysis of the 'H-'H vicinal coupling constants showed that the ring of the major anomer, 5-thio-a-~-glucopyranose, is slightly puckered in comparison to that of a-D-glUCOpy"IOSe. All the axial-axial couplings are smaller in the sulfur heterocycle, and, most critically, J1,z (an axial-equatorial coupling) also is smaller. The electronegativity change for an 0 to S change would have predicted an increase in J1,z. The observed decrease confirms the puckered distortion that is also a property of the unsubstituted heterocycle thiane. The 13C resonances were assigned by a series of selective 13C ('H) experimenta. The resonance positions are readily understood in terms of standard a, j3, and y shielding effects.