An EPR/ENDOR study of aminoxyls (nitroxides) capable of intramolecular bonding: hydroxyalkyl radical spin adducts of nitrones

Abstract

. Can. J . Chem. 66, 1901Chem. 66, (1988. A comparison of the effect of solvent and 13c labeling (of the radical addend) on the EPR (electron paramagnetic resonance) spectra of hydroxyalkyl vs. alkyl radical adducts of a-phenyl-N-tert-butyl nitrone (PBN) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) has been investigated. The solution ENDOR spectra in toluene and in ethanol are the first examples studied of aminoxyls with hydroxyl substituents in close proximity to the free radical centre. Diastereomeric mixtures of hydroxyalkyl radical adducts are clearly resolved by ENDOR spectroscopy. Conformations of these radicals have been assigned based on the 'H and I3c hyperfine splittings (HFS's) and by differential optimum ENDOR temperatures. Definitive assignments of carbon-centered radical adducts of DMPO and PBN are shown to be feasible by monitoring the p-I3C HFS's of the radical addend. Long-range y-H HFS's from the added radical group can be observed when the deuterated spin trap PBN-d,, is used. The production of 13c labeled hydroxyalkyl adducts of nitrones (e.g., DMPO-'3CH20H, from the reaction of hydroxyl radicals with added I3CH30H) is shown to be useful as an improved EPR spectroscopic method for the verification of the presence of hydroxyl radicals.D. LARRY HAIRE, YASHIGE KOTAKE et EDWARD G. JANZEN. Can. J. Chem. 66, 1901Chem. 66, (1988. On a effectue une Ctude comparative de l'effet de solvant et du marquage au I3C (du radical qui s'ajoute) sur les spectres en rksonance paramagnktique Clectronique d'adduits alkylCs vs. hydroxy-alkylts de l'a-phinyl N-tert-butyl nitrone (PBN) et de l'oxyde de la dimethyl-5,5 pyrroline (DMPO). Les spectres ENDOR, en solutions dans le toluene et dans l'ethanol, sont les premiers exemples de spectres de radicaux aminoxyles portant des substituants hydroxyles i proximite du centre radicalaire. La spectroscopic ENDOR permet de resoudre sans ambigui'tt les melanges diastCr6omeres des adduits radicalaires hydroxy-alkylCs. On a attribut les conformations de ces radicaux en se basant sur les couplages hyperfins du 'H et du I3C et sur les temperatures differentielles ENDOR optimales. On a dtmontrC que, si on determine les couplages hyperfins du p-l3C du radical ajoutC, il est possible de faire des attributions dtfinitives des adduits, du DMPO ainsi que du PBN, qui portent des centres radicalaires sur le carbone. Lorsqu'on utilise le piege i spin PBN-d14, on peut observer les couplages hyperfins du y-H i longue distance du groupement radicalaire qui a Ct C ajoutC. On a dkmontre que la formation d'adduits hydroxy-alkylCs des nitrones qui sont marquees au I3c (par exemple, le D M P O -~~C H~O H qui provient de la reaction de radicaux hydroxyles avec du ajoutC) est une mtthode en resonance paramagnttique Clectronique amCliorCe pour la verification de la presence de radicaux hydroxyles.[Traduit par la revue]

Unexpected Reaction of the Unsaturated Cluster Host and Catalyst [Pd3(μ3‐CO)(dppm)3]2+ with the Hydroxide Ion: Spectroscopic and Kinetic Evidence of an Inner‐Sphere Mechanism

“…Our experimental coupling constants (a b H = 19.1 G, a N = 13.93 G) are clearly different from those expected for a DMPO-OH adduct (in toluene: a b H = 13.75 G, a N = 12.10 G), [18] but are very close to those reported for a DMPO-alkyl adduct. [19] Similar experiments were carried out in DMSO instead of THF.…”

Chiral Spin Traps. The Spin Trapping Chemistry of 5-Methyl-5-phenylpyrroline-N-oxide (MPPO)

“…With 1% assumed to be the hydroperoxyl/superoxide radical. [6] is increased, the observed spectrum changes from purely Rib / hn r Rib* [7] hydroxyl adduct to purely hydroperoxyl adduct. Figure 3b shows a mixture spectrum due to hydroxyl, plus strong and Rib* / DH r Rib…”

Influence of preparation method on surface and bulk properties of sunlight-active Ti–W mixed oxide photocatalysts

“…Its EPR parameters (g ¼ 2.0056, a N ¼ 14.9 G and a H ¼ 14.9 G) are characteristic of DMPO-OH adducts formed upon trapping of OH radicals by the DMPO molecules. [30][31][32] Evolution of the DMPO-OH signal with irradiation time is presented in Fig. 7.…”