Abstract NMR‐Kontaktverschiebungen, Linienverbreiterungen und Relaxation wurden für einige weitere Alkohole mit einem Nitroxidradikal in Lösungen von Tetrachlorkohlenstoff untersucht. Für primäre Alkohole wurden Hyperfeinkopplungskonstanten der OH‐Protonen zwischen — 1,4 und — 1,5 MHz gefunden, für sekundare Alkohole von — 1,2 MHz und für tertiäre Alkohole von — 0,9 MHz. Eine mögliche Temperaturabhängigkeit der Kopplungskonstanten und die Spindichteverteilung im Alkoholmolekül werden diskutiert. Aus Messungen der Linienbreite und Relaxation bei verschiedenen Temperaturen und Frequenzen werden Aussagen über Bewegungsverhalten, Struktur und Lebensdauer der Komplexe abgeleitet. Die Diskussion faßt die Ergebnisse der drei Arbeiten dieser Serie zusammen.
The 23 Na and the 7 Li NMR spectra from several binary- and ternary alkali silicate and alkali borate glasses have been examined as a function of composition and temperature. At temperatures well below room temperature both the magnetic dipolar interactions between various nuclei and the electric quadrupolar interactions with the surroundings remain more or less the same in all the glasses. Upon increasing the temperature the width of the central transition of the 7 Li absorption decreases, the 23 Na dispersion changes from a quadrupolar to a more dipolar like shape, and important spin lattice relaxation is produced. Substitution of other alkali ions for lithium and sodium, respectively, affect the dynamic rather than the static behaviour of the glasses. The results are discussed with the assumption that the main contribution to the NMR signal is from nuclei belonging to alkali-rich regions which look similar in silicate and borate glasses, and for different alkali ions. The phenomena of motional narrowing, temperature dependent relaxation and drastic change of dispersion spectra are attributed to the diffusion of the alkali cations. From the relaxation data activation energies between 14 and 22 kcal/Mol have been obtained. Particular attention has been paid to the mixed alkali effect.
Wideline 1H NMR studies have been carried out in various hydrated layered chalcogenides of the type A+x(H2O)y [TaS2]x− at temperatures from 148 to 300 K, where A=Na, K, NH4, Cs, and Ca. Some measurements have been made at 77, 363, 398, and 425 K, respectively, and a sample with Nb instead of Ta has also been examined. Depending upon the temperature range and upon the particular compound, three different types of spectra have been observed. The rigid lattice H2O spectra are characterized by intra- and intermolecular dipole–dipole interactions. At elevated temperatures, the spectrum equals rather perfectly the theoretical shape of the proton spectrum for an isolated two-spin system. This suggests the occurance of a range of activated ordered mobility which is explained by a two-dimensional diffusion of water inside the interlayer space. For compounds with bilayers rather than monolayers of water, rotation of H2O about its C2 axis is also activated. This is supported by measurements of the spin–lattice relaxation time T1. Finally, an additional narrow line, which appears at high temperature, is attributed to a subphase of water undergoing random motion.
The frequency and temperature dependences of the 1 H NMR relaxation rates T 1 -1 for rotating CH 3 groups in solids look quite anomalous at intermediate hindering potential barriers. In order to explain the experimental behaviour and to extract parameters from the NMR T 1 experiments that account for tunnelling at low temperatures and random reorientation at elevated temperatures, we have calculated T 1 -1 vs. T -1 curves to be expected under various conditions. New experimental results for methyl iodide, methyl bromide, 3-methylthiophene, p-xylene, and methyl isocyanate have been fitted by this procedure and all the parameters that describe the motional behaviour have been derived. The single particle rotational potential has been determined using the first two terms of the Fourier expansion.
Statistical models that have been used so far for the description of relaxation and dynamic polarization in spin systems are extended to more general stochastic processes. The Campbell theorem provides a means of calculating a great number of spectral intensity functions. Almost any measured frequency- and temperature-dependence of relaxation rates and dynamic polarization coupling parameters can thus be interpreted from simple molecular physical concepts.
Für den Nachweis von engen magnetischen Kernresonanzlinien eignet sich eine Modulations-Nach-weistechnik, bei der die Modulationsperiode kleiner als beide Relaxationszeiten ist. Die komplizierten Modulationseffekte, die wiederholt mathematisch beschrieben worden sind, werden auf einfache Weise an Hand eines makroskopischen Modells zur Analyse des Bewegungsablaufes der Kernmagnetisierung verständlich gemacht. Mit der Methode des rotierenden Koordinatensystems läßt sich der Verlauf der Absorptionssignale in Abhängigkeit von den Versuchsbedingungen verstehen. Die gewonnenen Ergebnisse werden in einigen graphischen Darstellungen wiedergegeben, welche die praktische Anwendung erleichtern. Es wird weiter gezeigt, daß neben anderen Vorteilen die Empfindlichkeit besser als bei den sonst in der Kernresonanzspektroskopie meist üblichen Nachweismethoden ist.
