Electron spin resonance study of intermolecular cation exchange between sodium iodide and the ion pairs of sodium benzophenone and sodium naphthalene in tetrahydrofuran

Abstract

Intermolecular cation exchange between sodium iodide and sodium benzophenone and sodium naphthalene ion pairs in THF has been studied by e.s.r. linewidth measurements. For sodium benzophenone the plot of the reciprocal lifetime of a sodium spin state against sodium iodide concentration is markedly curved and not linear as would be expected if the exchange takes place in a single bimolecular reaction step. A mechanism which explains the curvature has been suggested in which the exchange involves an equilibrium between the two ion pairs and a dipole–dipole association ion quadruplet. The change in spin state of the sodium coupled to the benzophenone anion takes place by an internal re-arrangement in the ion quadruplet. Values for the equilibrium constant and for the velocity constant of the re-arrangement have been obtained. The reciprocal lifetime plot for sodium naphthalene is approximately linear and a value for the velocity constant for the bimolecular exchange reaction step has been obtained.