NEW 2-SUBSTITUTED PYRROLINE-N-OXIDES - AN EPR SOLVENT STUDY OF THE RADICAL SPIN ADDUCTS

Ten substituted 5,5-dimethyl-1-pyrroline-N-oxides as well as the paren t nitrene spin trap (DMPO) were prepared: 5,5-dimethyl-1-pyrroline-N-o xide, 2,5,5-trimethyl-1-pyrroline-N-oxide, 2-tert-butyl-5,5-dimethyl-1 -pyrroline-N-oxide, 2-phenyl-5,5-dimethyl-1-pyrroline-N-oxide, 2-d(5)- phenyl-5,5-dimethyl-1-pyrroline-N-oxide, yl-5,5-dimethyl-1-pyrroline-N -oxide-nitronyl-C-13, (4-fluorophenyl)-5,5-dimethyl-1-pyrroline-N-oxid e, (4-chlorophenyl)-5,5-dimethyl-1-pyrroline-N-oxide, ert-butylphenyl) -5,5-dimethyl-1-pyrroline-N-oxide, 2-(4-methylphenyl-5,5-dimethyl-1-py rroline-N-oxide and 2-(2- methylphenyl)-5,5-dimethyl-1-pyrroline-N-oxi de. Analytical (i.e. ERR-grade) samples of these novel cyclic nitrones were obtained and characterized by (among other methods) H-1 NMR spec troscopy. Reduction of DMPO and these various 2-substituted cyclic nit rones gave the corresponding cyclic N,N-dialkylhydroxylamines, whose s tructures and conformations were also analyzed by H-1 NMR spectroscopy . Air oxidation of these cyclic N,N-dialkylhydroxylamines provided acc ess to the EPR spectra of the hydrogen, methyl, tert-butyl, phenyl, d( 5)-phenyl, nitronyl-C-13-phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-ter t-butylphenyl, 4-methylphenyl and 2-methylphenyl cyclic aminoxyl (pyrr olidine N-oxyl nitroxide) radical spin adducts of DMPO. The N-14, C-13 (where applicable) and H-1 hyperfine splitting constants of these ami noxyl adducts in ten solvents of widely different polarities (e.g., he xane to water) were measured and the solvent effect on these parameter s was evaluated. It was found that for the various 2-substituted DMPO- type spin adducts both the nitrogen and beta-hydrogen EPR hyperfine sp littings correlated linearly (r(2) greater than or equal to 0.90) with typical solvent polarity parameters such as E(T(30)). The correlation between the nitrogen and beta-hydrogen hyperfine splitting constants were even more linear (r(2) greater than or equal to 0.97).