Hyperfine coupling constants, benzene

When ESR spectra were obtained for the benzene anion radical, [C6II6] and the methyl radical, CH3, the proton hyperfine coupling constants were found to be 3.75 and 23.0 G, respectively, i.e. they differ by about a factor of 6. Since the carbon atom of CH3 has a spin density corresponding to one unpaired electron and the benzene anion carries an electron spin density of 1/6, the two results suggest that the proton coupling to an electron in a n-orbital is proportional to the spin density on the adjacent carbon atom ... 

ESR spectra of isolated 24(00), 24(CO) and 24(CC) were measured in benzene at room temperature as shown in Fig. 9.11. The spectra of 24(00) and 24(CO) are five-line spectra, suggesting that the exchange interaction between the two nitro-nyl nitroxide radicals is much weaker than the hyperfine coupling constant (2//kB < 3 X 10 3 K). 

Figure 3 TF- SR spectra for positive muons implanted into benzene (A) the raw time-differential histogram recorded for the experiment (B) the Fourier transform of (A) showing the two transitions due to the CeHeMu radical (218.18 and 295.85 MHz, giving a hyperfine coupling constant of of 514.03 MHz) and the signal from muons in diamagnetic environments (27.1 MHz).

The hyperfine proton coupling constants aH are used for estimating local spin densities (at proton bearing centers p). The McConnell Equation 56 57) (Eq. 11) relates aH and qu 57). The proportionality constant Q was chosen for benzene radical-anion as —2.25 mT 56>. For larger jr-systems higher values of Q were used. An agreement between the local spin densities and the total one should be sought. The McLach-lan... 

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