Spectral and kinetic measurements on a series of persistent iminoxyl radicals

Post-Polymerization Modification of Polyethylene through Photochemical Oximation and Consecutive Ketonization

“…Based on all the obtained EPR data of the reaction between the model oxime compounds and t -BuONO, we propose that the formation of the ketone is the result of the formation of an iminoxyl radical species that is too reactive under the photochemical oximation reaction conditions and decomposes to the ketone, similar to what is observed in the literature. − , − The formation of the iminoxyl radical during the photochemical oximation reaction is most likely the result of hydrogen atom transfer (HAT) by a high local alkoxy radical or NO • concentrations near the oxime. The decomposition to the ketone requires a reaction pathway in which N 2 and N 2 O are released, which is in line with our observations ( Figure A).…”

“…The 14 N hyperfine coupling of ∼28–32 G is in line with values reported for the iminoxyl radical, and the 14 N hyperfine coupling of ∼14–16 G is in line with values reported for nitroxide-type radicals. − , − The EPR spectra of cyclohexanone oxime and 2-butanone oxime with 1.0 equiv of t -BuONO show only one species with a 14 N hyperfine coupling of ∼14–16 G, characteristic of the same nitroxide-type radicals ( Figures S112 and S113 ). For sterically unhindered iminoxyl radicals, such as 2-butanone iminoxyl, the rate of decay of this radical is reported to be 400 s –1 , which makes detection cumbersome.…”

Protein Modification at Tyrosine with Iminoxyl Radicals

“…Steric and electronic factors of oximes correlated with yield of the products; sterically less hindered oximes 1a and 1b resulted in lower yields than bulkier oximes 1c – 1e , with intermediate-size oxime 1c affording the highest yield (83%). The observed tendency is likely due to the balance between stability and reactivity of iminoxyl radicals, − which are in part dictated by the bond dissociation energy (BDE O–H ) of oximes’ O–H bonds . The conversion of oximes to iminoxyl radicals is facile for 1a – 1e , due to the great oxidation potential of CAN.…”

“…The conversion of oximes to iminoxyl radicals is facile for 1a – 1e , due to the great oxidation potential of CAN. Sterically less demanding iminoxyl radicals 1a and 1b are, however, prone to deactivation through self-dimerization. ,, Therefore, the concentration of iminoxyl radicals is higher according to the steric demands. Due to steric repulsion, however, the reactivity of iminoxyl radicals with the phenol group is lesser according to the steric demands ( 1c > 1d > 1e ).…”

O−H Bond Dissociation Enthalpies in Oximes: Order Restored

“…Rate constants were determined for the decomposition of t -Bu(1-Ad)CNOCH 2 Ph at 423 K and for five other RR‘CNOCH 2 Ph at 443 K (see Table ). All the reactions were extremely slow, and the samples (which had been sealed under vacuum in glass ampules) 19,39 had to be heated for many weeks for there to be sufficient decomposition of the O -benzyl ethers for the decomposition rate constants to be calculated. , Since good linear correlations of ln([oxime] t = t /[oxime] t =0 ) versus reaction time were obtained for all RR‘CNOCH 2 Ph studied (see Supporting Information), any radical chain or other types of induced decomposition reactions are likely to be of little or no importance even at this high temperature 3 Observed Rate Constants for Disappearance of RR‘CNOCH 2 Ph in Degassed tert -Butylbenzene at the Given Temperature, Estimated Activation Enthalpies for Thermal O−C Bond Scission, E a , and Calculated Gas Phase O−C and N−O BDEs at 298 K a RR‘ T /K10 8 k/s -1 E a b O−C BDE c,d N−O BDE c,d N−H BDE c,e Me Me − − − 48.6 51.2 90.2 Ph Ph 443 0.42 47.9 45.7 50.7 91.7 9-fluorenyl 443 0.61 47.5 46.4 53.6 92.4 Me 2 CH Me 2 CH 443 8.9 45.2 46.8 49.3 89.6 Me 3 C Me 2 CH 443 13.2 44.8 45.9 48.9 88.0 Me 3 C Me 3 C 443 23.7 44.3 41.9 43.8 86.5 Me 3 C E −1-Ad 423 17.7 42.5 41.6 43.1 86.1 Me 3 C Z −1-Ad 423 34.8 42.0 40.9 42.5 86.2 a Calculated gas-phase N−H BDEs at 298 K for RR‘CNH are presented for comparison.…”