关键词: 非对称性亚硝基自由基, ESR, 光化学反应氢键跳动频率

Abstract: In order to understand the simultaneous interactions of nitric oxide and reactive intermediates derived from ethanol in the blood stream and liver within our human body, we chose ethyl nitrite, a compound synthesized from ethanol and sodium nitrite at neutral pH value, equivalent to physiological conditions, to study the radical intermediates during photolysis within the ESR,cavity with various light power sources. Under a two-photon Chemical reaction pathway, three isomer radicals were formed and characterized by their ESR spectra. The intermolecular formation of these isomeric radicals and the unequivocal detection of two diastiomeric, two strongly intramolecular hydrogen bonded di-α-hydroxyethyl nitroxide radicals are of considerable interests by the investigation of dynamic alternate linewidth variations of the nitrogen isotropic hyperfine splittings.
Different kinetic flow experimental studies indicated one photon process for the formation of ethoxyl-ethyl nitroxides. Under a more intense light source, from the orbital interactions and correlation diagrams, the homolytic α-cleavage reaction similar to the n,π^* states of ketones (so-called "Norrish Type I" reaction) is initiated by the absorption of a photon to promote another n-orbital electron mainly on the oxygen atom of alkoxy group into the electrophilic half-filled π^*-orbital. Two-photon process will generate two (d,l and meso form) di-α-hydroxyethyl nitroxides.
The potential surfaces of the rotations of two methyl groups in both isomers were studied by the charm software. Due to van der waals interactions, the two methyl groups arehighly hindered rotated with approximately 150 kJ/mol in planar structure of the meso form of di-α-hydroxyethyl nitroxide, where the two methyl groups in the d,l form is about 3.3kJ/mol. The assignment of the β-proton hyperfine splitting constants of the two isomers are based on molecular models and McConnell's equation. Their production rates are asymmetrical in solution with 60% for meso-form and 40% for d,1-form. Based on the alternate linewidth effects of the nitrogen hyperfine splittings, the jump rates of the two hydroxyl protons in the planar di-α-hydroxyethyl nitrokides are estimated to be about l0^-ll s.

Key words: Asymmetrical nitroxide radicals, ESR, Photochemical reaction, Hydrogenbond jump rate