The absorption spectra in the region 400-1000 mp of a number of alkali-metal complexes have been measured in dioxan solution. Beer's law was found to hold in all cases of ketyl complexes for which detailed measurements were made. This provides conclusive evidence that the complexes exist in solution (10-3 to 5 x 10-5 M) as monomeric ionpairs. It has been found that, for a given radical anion, the frequency Crn of the maximum of an absorption peak shifts towards the red as the radius r, of the alkali metal cation increases and there is an approximately linear relationship between fjrn and l/(rc + 2).Using this, extrapolated values for the frequency of the maximum for the isolated solvated anion have been obtained.
There are, however, a small group of compounds, not halides, investigated by Bawn and A. G. Evans (Trans. F u m d a y SOC., 1937, 33, 1571, 1580), which involve a three-body collision (see also ref. 2).
The Arrhenius parameters for the two-site jumping of the potassium cation in p-beiuosemiquinone ion pairs in DME have been determined by comparing computed line width and line amplitude ratios with those derived from experimental spectra over the temperature range -10 to f90"C.The results were E = 3-4f 1 kcaI mole-1 and log,,A = 9.5 10.5. The A factor indicates a negative entropy of activation for the intramolecular process and this is discussed. A study of two-site jumping of alkali metal ions in 2,5-di-tert butyl p-benzosemiquinone ion pairs in DME has been described. The rate of jumping increases along the series N a t K< Rb. An approximate value for the activation energy of the process has been determined for the potassium derivative.
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