Solvent effects on the nitrogen and β-hydrogen hyperfine splitting constants of aminoxyl radicals obtained in spin trapping experiments

Abstract

The nitrogen and β-hydrogen hyperfine splitting constants (hfsc) for phenyl, 4-nitrophenyl, 4-pyridyl, benzoyl, and trichloromethyl spin adducts of α-phenyl tert-butyl nitrone (PBN) as well as for the tert-butoxyl adduct of 5,5-dimethylpyrroline-N-oxide (DMPO) have been obtained as a function of solvent (30 solvents). A useful linear relationship between the β-H hfsc and the N-hfsc of each aminoxyl is found except for the benzoyl adduct of PBN. Some speculations regarding the structural significance of these correlations is presented.

The benzaldehyde oxidation paradox explained by the interception of peroxy radical by benzyl alcohol

“…Spin adduct I, observed only under anaerobic conditions, is an artefact not connected with the main autoxidation reaction and is believed to be a nitroxyl radical generated by nucleophile addition to PBN followed by oxidation 33 . On the other hand spin adduct II, also detected under anaerobic conditions, can be easily assigned to the benzoyl radical (PhCO ) 34,35 . Under subsequent aerobic conditions, a competition for the benzoyl radicals arises between PBN and dioxygen; since adduct II is no longer detected under the aerobic conditions, it is evident that oxygen trapping dominates.…”

Spin trapping chemistry of acyl radicals

“…The plot of upH against uN shows considerable scatter and the effect of polarity on these parameters is not very large. 6 Armed with a dependable assignment for the benzoyl adduct of PBN, spectra obtained from aged benzaldehyde not purified by distillation under nitrogen could be analyzed and understood. When unpurified benzaldehyde was reacted with DBPO in benzene the EPR spectrum pattern consists of two sets of triplets of doublets (spectrum not shown).…”

Preparation of N-aryl-ketonitrone spin traps

“…Moreover, the EPR spectrum of this adduct was recorded in a methanol/water medium, by increasing the methanol ratio from 1 to 100 %. As can be seen from Figure 2, the hfcc a N , determined after computer simulation of the signal, was thus found to decrease linearly from 12.0 G to 11.2 G. Though the variation of a N with the medium polarity is not unusual [5,40], its amplitude is rather high. By comparison, the EPR signal of the adduct PBN/ • CH 2 OH shows an a N value decreasing from 16.0 G in water to 15.6 G in 100 % methanol [41,42].…”