Electron spin resonance spectra solution

Fig. 3. Electron spin resonance spectrum of ethyl radical generated during photolysis of an aqueous acidic solution of Ce(IV) and propionic acid at 77 °C. The scale at lower right-hand-side = 50 G.

Fig. 14. Electron spin resonance spectrum of a frozen solution of rubidium in HMPA, at high machine amplification. The full lines show the variation of resonant field position with A for ge = 1.99800, and a microwave frequency of 9.1735 GHz. The lines are anchored at the crossovers of the MG species (A = 251.3 G). Positions of the Mc, M , ME, Mg, Mh, and M, absorptions are indicated. Reprinted with permission from R. Catterall and P. P. Edwards, Journal of Physical Chemistry, 79, 3010 (1975). Copyright 1975 American Chemical Society.

ESR (Electron Spin Resonance) spectrum (Fig. 1.2) recorded during electrolysis of DMPO (5.5 dimethyl-1-pyrroline-N-oxide) solution on BDD confirms the formation of OH during anodic polarization of diamond electrodes. It has been reported that the BDD-hydroxyl radical interaction is so weak (no free p or d orbitals on BDD) that the OH can even be considered as quasi-free. These quasi-ffee hydroxyl... 

Figure 3.6 Electron spin resonance spectrum of the p-superoxo complex of an axially coordinated imidazole derivative of a Co-Co face-to-face (Co-Co 5) porphyrin in toluene-dichloromethane solutions recorded at room temperature. A simplified schematic structure of the metal microenvironment of the proposed transtype adduct is shown in the insert.

Tetraphenylcyclobutadienepalladium halides such as the chloride (LIV) react very readily with phosphines, a qualitative order of reactivity being tri- -butylphosphine > l,2-bis(diphenylphosphino)ethane > triphenylphosphine (24, 69). No adducts have been isolated, but when the reactions are run at 25°C in benzene in the absence of air, a deep green solution is obtained, which persists for some time in the case of triphenylphosphine. This solution contains a strongly paramagnetic species, the electron spin resonance spectrum of which is independent of the phosphine... 

An argument in favor of such a formulation is that the endb-ethoxytetra-phenylcyclobutenylpalladium chloride dimer (LXXII) (Section IV, E) on treatment with phosphines gives a solution with a very similar electron spin resonance spectrum, thought to be due to (LXXIII) (25). 

Solutions of sodium-naphthalene in tetrahydrofuran are dark green, electrically conducting because the compound is a salt Na (THF) CioHs", and paramagnetic because of the extra electron which is in a singly occupied 7r-orbital. Information about the distribution of the unpaired electron about its various possible positions in the anion can in suitable cases be derived from the electron spin resonance spectrum. If the orbital occupied by the unpaired electron in a hydrocarbon anion is non-degenerate, as is the case with naphthalene and anthracene, then a second electron (formation of anion ) would enter the same orbital and both the paramagnetism and e.s.r. spectra disappear. 

The electron spin resonance of the nitroxalkylcorrinoids can be readily observed in aqueous solution at room temperature. Both the cobalamin and cobinamide show nitrogen hyperfine coupling constants of 17.2 gauss. A typical spectrum is shown in Fig. 20. The line widths for the low, intermediate, and high field peaks are 1.87, 1.87, and 2.20... 

Background copper levels in seawater have been measured by electron spin resonance techniques [300]. The copper was extracted from the seawater into a solution of 8-hydroxyquinoline in ethyl propionate (3 ml extractant per 100 ml seawater), and the organic phase (1 ml) was introduced into the electron spin resonance tube for analysis. Signal-to-noise ratio was very good for the four-line spectrum of the sample and of the sample spiked with 4 and 8ng Cu2+. The graph of signal intensity versus concentration of copper was rectilinear over the range 2-10 xg/l of seawater, and the coefficient of variation was 3%. 

From the point of view of the solvent influenee, there are three features of an electron spin resonance (ESR) speetrum of interest for an organic radical measured in solution the gf-factor of the radical, the isotropie hyperfine splitting (HFS) constant a of any nucleus with nonzero spin in the moleeule, and the widths of the various lines in the spectrum [2, 183-186, 390]. The g -faetor determines the magnetic field at which the unpaired electron of the free radieal will resonate at the fixed frequency of the ESR spectrometer (usually 9.5 GHz). The isotropie HFS constants are related to the distribution of the Ti-electron spin density (also ealled spin population) of r-radicals. Line-width effects are correlated with temperature-dependent dynamic processes such as internal rotations and electron-transfer reaetions. Some reviews on organic radicals in solution are given in reference [390]. 

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