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MO calculations predict that the monoanion of 1,3,5-triphmylbenzene (Tpb) is in an orbitally degenerate ground state. Nevertheless, the ESR spectrum in liquid NHj is well resolved; the derivative linewidth is equal to 0.06 Oe only. The g value and the electronic relaxation times Ti and T-t were comparable in magnitude to those of orbitally nondegenerate radicals. It is suggested that twisting of the phenyl rings out of the plane of the molecule, which may lift the orbital degeneracy, is the principal reason of this behavior. 'H and ZD N M R experiments were performed on a reduced sample of Tpb, containing both normal and perdeutero-Tpb. From the Fermi contact shifts signs and magnitudes of all hyperfine splitting constants have been determined, and they agreed very well with the ESR splitting constants. From the proton linewidths the electronic and dipolar correlation times were inferred. Quadrupole coupling constants for all deuterium nuclei were calculated from the 2D linewidths.

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Abstract:The optical absorption spectra have been measured of alkali metal reduced solutions of triphenylene in 2-methyltetrahydrofuran from -155 to +75°. Several ion pairs have been observed. A linear correlation between frequency of absorption and reciprocal of catioh radius has been demonstrated for both solvated and contact ion pairs. The low-temperature spectra show a clear equilibrium between two types of ion pairs at high radical concentrations. lts thermodynamic parameters have been measured for sodium, potassium, and rubidium triphenylene solutions. At low-radical concentration dissociation occurs into free ions. The dissociation enthalpy and entropy have been determined. The high-temperature spectra show a gradual increase in frequency as the temperature is increased. This shift has been interpreted as due to an equilibrium between solvated and contact ion pairs. For potassium, rubidium, and cesium triphenylene solutions the thermodynamic constants characterizing the latter equilibrium have been calculated.