Electron spin resonance studies of kinetic effects of substituent and crown ether on intramolecular sodium cation exchange in 2,5-di-tert-amyl- and 2,5-di-tert-butyl-1,4-benzoquinone radical anions

Upon an addition of crown ethers to a solution of 2,5-di-tert-amyl-1,4-benzoquinone (2,5-DAQ) and 2,5-di-tert-butyl-1,4-benzoquinone (2,5-DBQ) radical anions, the significant broadening of the two-center lines was observed in their electron spin resonance (ESR) spectra. The formation constants for the complexation of sodium cation with three kinds of crown ethers in 2,5-DAQ and 2,5-DBQ radical ion pairs were estimated, and the intramolecular two-site jumping rates of sodium cation complexed with crown ethers were determined. Differential effects of steric and crown ether were found in the intramolecular sodium cation migration. The stabilization of inclusion complex of sodium cation with crown ethers gives rise to the acceleration effects on the rates of intramolecular migration of cation/crown-ether complex. Based on the results, a kinetic explanation for the intramolecular sodium cation migration in the presence of crown ethers was given.