Three novel spin-labeled crown ethers. [2,2-(sym-dibenzo-16-crown-5)-4,4-dimethyloxazolidinyl-N-oxyl; 2,2-(sym-dibenzo-16-crown-5)-4,4,5,5-tetramethylimidazolinyl-N-oxyl; and 3-carboxy-2,2,5,5-tetramethyl-3-pyrrolinyl-l-oxy hydroxy-sym-dibenzo-16-crown-5 ester]
The following nitroxide spin-labeled crown ethers have been synthesized: 2,2-(sym-dibenzo-16-crown-5)-4,4-dimethyloxazolidinyl-N-oxyl (1), 2,2-(sym-dibenzo-16-crown-5)-4,4,5,5-tetramethylimidazolinyl-N-oxyl (2), and 3-carboxy-2,2,5,5-tetramethyl-3-pyrrolinyl-l-oxy hydroxy-sym-dibenzo-16-crown-5 ester (3). 1 and 2 are characterized by having the nitroxide near the crown cavity and rigidly bound to a ring carbon atom of the crown. 1-3 have been studied by EPR, and the proton hyperfine splittings have been determined by second harmonic out-of-phase detection. The values obtained for the proton hyperfine splittings of 1 were compared to those determined by ENDOR and found to agree within experimental error. EPR studies of hyperfine splitting constants and Heisenberg spin exchange suggest that these spin-labeled crownsmore »