Effect of Ion Pairing on the g Value of the Naphthalene Anion Radical

Measurements have been made of the $g$ values of the naphthalene radical anion associated with several alkali‐metal cations at a series of temperatures and in different solvents. It has been suggested previously that the temperature dependences of the $g$ factors of spectra exhibiting alkali‐metal splittings can be explained either in terms of equilibrium changes between two paired species (Hirota model) or in terms of changes in the populations of the vibrational energy levels of a paired species of fixed electronic structure (Atherton–Weissman model). Evidence is presented to show that the Hirota model adequately accounts for the g‐factor variations of the sodium naphthalenide ion pair in tetrahydrofuran, but not for the cesium naphthalenide ion pair in 1,2‐dimethoxyethane. It is argued that the latter ion pair is probably a tight ion pair which does not incorporate solvent molecules, and that the variations of the spectral parameters of such complexes are best described by the Atherton–Weissman model.