ESR simulation

The structure of free radical 85 produced by dissociation of a stannyl benzopinacolate, was investigated by ESR spectroscopy and confirmed by ESR simulation. Free radical 85 is a good source for stannyl free radicals, as shown in reaction 10262. 

We cordially thank Professor Satohiro Yoshida of Kyoto University for providing the ESR simulator program. 

Computational work had also begun to flourish in the group of Charles Coulson in the Mathematical Institute at Oxford. Not only was molecular electronic structure work done there but also heavy-particle scattering, and quite a lot of that aspect of the work can be discovered by reading the book by Levine, who was in the Mathematical Institute at the time. Computational work had also begun in the Physical Chemistry Laboratory chiefly with Peter Atkins and his students with their interests in NMR and ESR simulation, and... 

RIGMAT, MULTIP, HMLT A suite of ESR simulation programs has been prepared by Dr. C. Chachaty and is available free of charge at http //www.esr-spectsim-softw.fr/programs. 

ESR simulations revealed that the spectral line-shape of (NO)2 bi-radical is very sensitive with respect to the relative orientations of the g and the D tensors and the principal axes of gzz and Dzz cannot deviate by more than 30 (corresponding to angle 6 in Scheme 6.1) from each other in this model. In the simulations the principal values of the g-tensors of each NO molecule were assumed to be the same as the experimental ones for the (NO)2 biradical with the principal axes parallel and perpendicular to the N—O bond and along the common x-axis (g = 2.0042) and the direction of Dzz was taken along the line connecting the midpoints of the two N—O bonds as shown below [13, 36]. 

Other alkali metals also studied. K eoupling from ESR simulation, sign not determined. MO ealeulations undertaken. 

A number of molecular properties can be computed. These include ESR and NMR simulations. Hyperpolarizabilities and Raman intensities are computed using the TDDFT method. The population analysis algorithm breaks down the wave function by molecular fragments. IR intensities can be computed along with frequency calculations. 

The ESR spectrum of C6H6 " trapped in CFCI3 at 15 K is shown in Figure la and agrees with that reported previously [18]. The principal values of the hyperfine coupling were obtained from previous ESR and ENDOR measurements [17, 18]. The best agreement with experiment was obtained with the axes oriented as in Table 4. In the latter study, the simulated ENDOR spectra were insensitive to the orientation of the tensor axes, however, and the assignment was made on the basis of molecular orbital calculations [9]. The tensor data are reproduced here for convenience (see Table 4). 

Figure 1. ESR spectra at some temperatures of X-irradiated polycrystalline frozen solutions (c a 1 mol%) of C5H5 and CgH5D, respectively, a) at 15 K. b) simulated spectrum by using the parameters shown in Table 4. c) 05 150 " " at 30 K in CFCI3. d) simulation using hyperfme coupling data shown in Table 4 for a mixture of component 1 component 2 of C6H5D . The ratio 1 2 = 0.38 0.62 obtained from the component analysis of Figure 2 was employed.

Table 4 The g and hyperfine tensors (in Gauss) used in the ESR and ENDOR simulations of C6H5D + in CFCI3 at 30 K.

Figure 2. Component analysis of an X-irradiated polycrystalline frozen solution (c a 1 mol%) of C6H5D in CFCI3. a) simulated components 1 (dashed) and 2 (solid) using hyperfine coupling data from ENDOR (Table 4). b) experimental (solid) and fitted (dashed) ESR spectra of CgH5D...

Hyde, J. S. and W. K. Subczynski. 1984. Simulation of ESR spectra of the oxygen-sensitive spin-label probe CTPO. J. Magn. Reson. 56 125-130. 

Figure 6 Simulated ESR spectra of nitroxides (a) in the absence of magnetic field gradient (b) ID image for a homogenous radical distribution (in the presence of a gradient) and (c) ID image for radicals present only in thin layers near both surfaces of the plaque (in the presence of a gradient).

Simulation programs for the ESR line shapes of peroxy radicals for specific models of dynamics have been developed for the study of oxidative degradation of polymers due to ionizing radiation [66]. The motional mechanism of the peroxy radicals, ROO, was deduced by simulation of the temperature dependence of the spectra, and a correlation between dynamics and reactivity has been established. In general, peroxy radicals at the chain ends are less stable and more reactive. This approach has been extended to protiated polymers, for instance polyethylene and polypropylene (PP) [67],... 

First, we examined the efficiency of the initiation process. A solution of buthyllithium was added to a THF solution of 7 at -70°C. The color of the solution turned to red immediately and a strong ESR signal was observed with a well separated hyperfme structure. The observed radical species was identified as the anion radical of 2-butyl-l,l,2,2-tetramethyldisilanyl-substituted biphenyl by computational simulation as well as by comparison with the spectra of a model compound. The anion radical should be a product of a single electron transfer (SET) process from buthyllithium to the monomer. Since no polymeric product was obtained under the above-mentioned conditions, the SET process is an undesired side reaction of the initiation and one of the reasons why more higher molecular weight polymer was observed than expected. ... 

Figure 2.2 ESR spectrum of the naphthalene anion radical 1 simulated using hyperfine couplings given in Table 2.1.

Figure 2.3 ESR spectrum of the potassium salt of pyrazine radical anion simulated using hyperfine couplings from ref. 2.

ESR spectrum of the methyl radical, CH3 (note discontinuities in magnetic field axis). Simulated using hyperfine splitting from ref. 3 and eqn (2.5). 

Figure 2.8 ESR spectra resulting from the reduction of PhCN (bottom) and />-F-PhCN (top). The top spectrum is identical to that of the 4,4 -dicyanobiphenyl anion radical. (Spectra were simulated using hyperfine couplings with permission from ref. 16, copyright (1963) American Chemical Society.)...

Figure 2.10 ESR spectra of o-, m-, and p-xylene radical anions (see text for assignment of spectra). Spectrum (a) was simulated with permission using hyperfine parameters from Ref. 17b, copyright (1964) American Institute of Physics spectra (b) and (c) were simulated with permission using hyperfine parameters from ref. 17a, copyright (1961) Taylor and Francis (www.tandk. co.uk).

Figure 4.3 [E] Computer-simulated first-derivative ESR powder spectrum of Cu(acac)2.

A good example of the effect of g- and hyperfine matrix axis noncoincidence is the ESR spectrum of [CpCr(CO)2NO] , studied by Geiger and co-workers 39 a simulation is shown in Figure 4.7. 

Figure 4.12 [E] Computer-simulated ESR spectra for a hypothetical low-spin Mn(n) radical with g = (2.100, 2.050, 2.000), AMn = (150, 25, 25) x 10-4 cm-1, for various values of / , the Euler angle between the g-matrix and hyper-...

Figure 4.13 Simulation of ESR spectrum of the above cobalt dithiolene complex in frozen toluene at 77 K.

Whigh = 4.1 G (the —3/2 line was used since the —1/2 line was subject to destructive interferences by a divergence feature). The simulation in Figure 4.14(c) is based on wg = 0.0049 G. A very similar explanation deals with the broader low-field features in the ESR spectrum of [Cr(CO)2(PMe3)(r -C5Ph5)] (ref. 28) (Figure 4.10). 

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