Electron hyperfine splitting

Anisotropy due to nuclear-electron hyperfine splitting, to spin-orbit coupling ( -factor), and particularly to strong electron-electron dipolar splitting in molecular triplets and radical pairs, provides a great deal of orientational information. It also makes it possible to shift peak positions in the spectrum, creating new windows through which to observe minor components that would be completely obscured in powder spectra. 

Transannular interaction via the electron-delocalization mechanism was found, but lessened by 10-15% for the ligand superhyperfine splitting and 30-35% for the hyperfine splitting (62) in the epr spectrum. The crystal structure of [VOS2CNEt2)2] shows that the molecular core has the expected C2V symmetry [V-0 = 159.1(4), V-S = 138.7(2)-241.0(2) pm] (63). Magnetic and spectral data provided evidence for a tetragonal, pyramidal structure (VII) for these complexes. Like many other coordinatively unsaturated, metal... 

Work of several types has been carried out. As long ago as 1970 Strom and Norton studied electron-withdrawal by substituents containing Group IV and Group VI elements through their effect on ESR methyl hyperfine splitting in l-phenyl-1,2-propanesemidiones 39. 

Note that the values of are orders of magnitude larger than the A values given for the hyperfine splitting of an EPR spectrum (or ENDOR spectrum) in units of the field sweep necessary to obtain electron spin resonance. These are usually on the order of only 10 mT or less ... 

As with the nitroxalkylcobalamins (119) and cobinamides, the co-binamides in which nitroxide is coordinated show electron spin resonance spectra very similar to the spectrum of free nitroxide. The high field line is not broadened as much as in the spectrum of a nitroxalkyl-cobinamide. No hyperfine splitting from methyl protons in the 2 or 6 positions can be observed for the bound nitroxide. However, treatment of the coordinate spin labeled compounds with cyanide releases the nitroxide. When this happens, the proton hyperfine can be observed (Fig. 25). Thus treatment with cyanide simply displaces the nitroxide and a spectrum for free nitroxide is observed. 

Hyperfine splitting. As was discussed above, one consequence of placing a free electron onto a molecule is to alter its 0-value. Another is that the electron spin comes under the influence of any magnetic nuclei present in the radical, with the result that the spectrum is split into a number of lines centred on the position of the single resonance expected for the simple /transition discussed above. This hyperfine structure is the most useful characteristic ofepr spectra in the identification of an unknown radical species. 

Figure 2.98 The hyperfine splitting patterns resulting from the interaction of an electron spin with two protons with (a) different hyperfine coupling constants and (b) the same hyperfine...

Based on hyperfine splittings used for the simulation of the 109Ag 13CH2OH+ spectrum it was calculated that the unpaired electron in the silver hydroxymethyl radical is localised to the extent of 29% on Ag and 46% on C and H nuclei. By comparison these spin... 

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