Nuclear magnetic resonance has been carried out on all nuclei with nonzero magnetic moments present in the alkali ion pairs of deuterated and nondeuterated naphthalene radical anion in 1,2-dimethoxyethane. Both the sign and magnitude of the hyperfine splitting constant (h.f.s.c.) were measured, the alkali h.f.s.c. being studied as a function of the temperature. The Li and Na h.f.s.c. appear to be positive, those of Rb and Cs are negative, whereas that of K changes sign with temperature.The proton and deuterium linewidths were studied as a function of the concentration and were found to vary linearly with the reciprocal of the concentration, pointing to the predominance of the Fermi contact interaction.An analysis of the alkali linewidth is given in terms of the intramolecular relaxation processes. Especially in cases where two isotopes could be studied, i.e. (1H , 2D), (6Li, 7Li) and (85Rb, 87Rb), a quantitative interpretation is presented. . I n t r o d u c t i o nSince the pioneering work o f Atherton and Weissman on the association between sodium and naphthalenide ions [1], many papers have appeared on E.S.R. studies o f ion pairs and much information on alkali metal hyperfine splitting constants (h.f.s.c.) has been collected [2], The alkali metal hyperfine coupling was found to be very sensitive to the solvent and the temperature, suggesting that transfer o f spin density from the aromatic radical to the metal proceeds in a complex manner. Unfortunately E.S.R. experiments only give the absolute value o f the h.f.s.c., whereas in determining the mechanism o f spin transfer the sign o f the h.f.s.c. is also o f importance. D e Boer [3], in an E.S.R. study o f the pyracene anion radical, observed that the Cs and Rb h.f.s.c. exhibited an anomalous temperature dependence. He suggested that the h.f.s.c. o f these ions could be negative as well as positive.Negative alkali spin densities were also proposed by Dodson and Reddoch [4] and Hirota [5], in studying the alkali naphthalene ion pairs. They noticed that regularly decreasing plots o f spin density at the alkali nucleus (calculated as the ratio o f the observed hyperfine splitting in the ion pair to that o f the atom in the gas phase [6]) versus the radius r of the alkali ion, were obtained if the spin density at the Rb and Cs nucleus was taken negative. This correlation between spin density and ionic radius has also been observed for other systems, e.g. alkali anthracenides [5],

No abstract

The proton N .M .R. spectra of biphenyl-, fiuorenone-and phenanthreneand the deuterium N .M .R. spectra of biphenyl-dlO-and phenanthrene-dlOhave been measured in ethereal solutions at room temperature. Sign and magnitude of the hyperfine splitting constants derived from the measured contact shifts are reported and compared with E.S.R. data and predictions from theory. From the measured proton and deuterium relaxation times values for the electron spin and the rotational correlation times have been obtained.

No abstract

The proton relaxation has been studied in methyl substituted aromatic radical ions in solution. The linewidth parameter T 2 of the protons in such radicals is goveméd by two intramolecular interactions, namely, the Fermi contact interaction and the anisotropic dipolar interaction. For the methyl protons the interactions are modulated in time by both intemal rotation and tumbling of the whole molecule in solution. Equations have been derived to account for the effect of these motions on the CH3 proton linewidth. The resulting formulas are used to analyze the NMR proton linewidths for the anion of 3, 3'-dimethylbiphenyl.