Hyperfine splitting constant, electron

The electron spin resonance (ESR) spectra of the radical anion of 2,2 -bipyridine, sometimes in the form of its alkali metal com-plgx, 71.175,177.299-304 radical anion of 3,3 -bipyridine, ° and the radical anion of 4,4 -bipyridine, ° ° usually obtained by reduction of the bipyridines with an alkali metal, have been measured, and hyperfine splitting constants were assigned. Related biradical species have also been investigated. The ESR spectrum of the 4,4 -bipyridinium radical cation, of which... 

Here / is a nuelear spin, F is the full momentum of the system, and J is the full electron momentum. The hyperfine splitting constants are expressed through the standard radial integrals ... 

As mentioned for the relationship between the PE spectrum of a parent molecule and the electronic spectrum of its radical cation, any close correspondence between the electronic spectra of anions and cations or their hyperfine coupling patterns holds only for alternant hydrocarbons. The anions and cations of nonalternant hydrocarbons (e.g., azulene) have significantly different hyperfine patterns. Azulene radical anion has major hyperfine splitting constants (hfcs) on carbons 6, and 4,8 (flH = 0-91 mT, H-6 ah = 0-65 mT, H-4,8 ah = 0-38 mT, H-2) in contrast, the radical cation has major hfcs on carbons 1 and 3 (ah = 1.065 mT, H-1,3 Ah = 0.152 mT, H-2 ah = 0.415 mT, H-5,7 ah = 0.112 mT, H-6). °°... 

The electron spin resonance (ESR) spectrum of the radical anion of 1,10-phenanthroline obtained by reduction of 1,10-phenanthroline with sodium has been measured, and hyperfine splitting constants were assigned.116... 

According to Table I, the small Co2+ hyperfine splitting constants indicate that the unpaired electron must be largely localized on the coordinated oxygen molecule. If the unpaired electron is localized in only one d orbital, the hyperfine tensor can be resolved into an isotropic and anisotropic part in the form ... 

The N//-azaindole 40 with X = 6 is paramagnetic. Its electron spin resonance (ESR) spectrum (in DMSO) shows a characteristic triplet with a 1 1 1 intensity and the hyperfine splitting constant An = 16.04 Oe. 

The hyperfine splitting constant ay has units of energy and is a characteristic parameter for the interaction of the unpaired electron with a nucleus of type /. It is the analog of the NMR J spin-spin constant describing the magnetic coupling between two nuclei. 

Figure 3 Solution spectrum of a typical nitroxide radical where the unpaired electron is mainly interacting (i.e., hyperfine interaction) with the nitrogen nucleus. Since nitrogen is predominantly the isotope, the line is equally split (hyperfine splitting constant) into three (ra/ = - -1, 0, — 1) lines...

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