Cation hyperfine splitting

A similar change from 9 to 5 lines results sometimes when a simple salt with a common cation is added. In this case reaction (3.2) occurs, so that the lifetimes of the asymmetric units are reduced, but different sodium ions (with varying nuclear spins) are involved, so that the cation hyperfine splitting is lost at the same rate. As usual, at intermediate rates, lines become broad and from the width increments, rates and activation energies and entropies can be obtained. 

Tlie following summarizes g-values and hyperfine splitting values by ( h) and by ( 33s) in natural abundance for the representative 1,2-dithiete radical cations. 

In Table 3 are listed the proton hyperfine splittings (o ) for. the anion and cation radicals of heptafulvalene, calculated using McConnell s... 

For example, we can tell that the paramagnetic cation giving rise to the EPR signal in Figure 8.6 is non-planar, which is quite unusual for such an aromatic radical cation, a fact we know from additional computations based on the hyperfine splitting pattern. 

For instance, nitration of naphthalene, azulene, biphenylene, and triphenylene proceeds preferentially in positions with the greatest constant of hyperfine splitting at the hydrogen atom in ESR spectra of corresponding cation-radicals. The constant is known to be proportional to the spin density on the carbon atom bearing the mentioned hydrogen. It is important, however, that the same orientation is also observed at classical mechanism of nitration in cases of naphthalene, azulene, and biphenylene, but not triphenylene (see Todres 1985). 

As Stated in the previous section, reduction of thieno[3,2-2 ]thiophene (2) with Na-K alloy at —100 results in the formation of a radical-anion. With AlClj in nitromethane at —20°, or SbClj in methylene chloride at —60°, a radical-cation was obtained. The experimental hyperfine splitting constants (HFSC) data are shown in Eq. (73). 

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... 

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). °°... 

Recently, radical cations of other conjugated sulfur compounds70 have been prepared the radicals derived from 1,4-dithiin (56), 1,4-benzodithiin (57), and three derivatives of radicals 55 and 57. Analysis of the ESR spectra of these derivatives permitted the assignment of hyperfine-splitting constants to the six chemically non-equivalent... 

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