Direct ESR Evidence for Sodium Selective, Intramolecular Ion Pairing in Redox-Switched Nitrogen-Pivot Lariat Ethers

Article abstract of DOI:10.1021/ja00274a047

N-(2-Nitrobenzyl)aza-15-crown-5, 1, and the sidearm hexadeuterio analogue 2 have been reduced electrochemically to their corresponding radical anion forms and analyzed by ESR.Addition of Li(1+), Na(1+), or K(1+) to the solutions leads to changes in the ESR spectra but the changes are most marked when Na(1+) is present.Essentially no change is observed in the ESR spectrum of 2-nitrotoluene, confirming that both macroring and sidearm must be involved for the intramolecular ion pair to be stable.The radical anion sidearm compexes must be relatively rigid species since the strongest sidearm interaction is observed with Na(1+) cation which is closest in size to the cavity formed by the cooperating macroring and sidearm.