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The influence of ion-pair equilibria can be neglected since the hyperfine data are not substantially affected when replacing the potassium/crown ether counterion by benzyltrimethylammonium (Table II). Moreover, the results obtained in 8CB demonstrate that the isotropic hyperfine couplings are not significantly altered when passing from the isotropic to the smectic phase. Consequently, the phase transition is not accompanied by a substantial change in the solvation or the ion-pair structure. It should be noted that the isotropic coupling constants of 2 in liquid crystalline solvents are in agreement with those obtained in dimethylformamide.15 A similar invariance is found for the large coupling of 1 (-2.73 ± 0.01 MHz, ethanol or toluene), whereas the small coupling is strongly solvent and temperature dependent (-1.53 MHz, ethanol, 210 K;-1.33 MHz, toluene, 210 K; -0.89 MHz, 8CB, 315 K). This probably accounts for the anomalous temperature behavior of the shifts of 1 in "phase IV" (Table I).Since there is considerable interest in studying quadrupole splittings by means of ENDOR in liquid crystals, it is noteworthy that we succeeded in observing deuterium quadrupole splittings in the ENDOR spectrum of 3. The splitting amounts to about 160 kHz for the para positions (8CB, 294 K), whereas splittings for the ortho or meta positions could not be resolved.2H ENDOR quadrupole splittings are strongly dependent on the orientation of the C-D bond, being largest for an orientation parallel to the magnetic field.3 Therefore, a trans configuration of 3 can be assumed, and the long axes of the molecules are preferentially oriented parallel to the long axes of the solvent molecules. Further ENDOR studies of radical ions in liquid crystals are in progress.

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