Calculated spin densities

The calculated bond lengths for the 2 structure of the anion radical of heptafulvalene shown in Fig. 7 indicate that in one of the ring there exists a significant bond fixation to the same extent as that in the neutral heptafulvalene, while in the other ring bond lengths are nearly equalized. The calculated spin densities, presented in Table 3, indicate that the unpaired spin is localized essentially on the latter ring. 

Figure 2.12. BP/DNP calculated spin density contour of the r/-/V 2CuNO nM5 complex and for the NO molecule, showing two possible routes of NO attachment an inner-sphere attack at the metal center (slim arrow) and an outer-sphere attack at the NO ligand (bold arrow) (after [75]).

TABLE 2. Relationship between calculated spin densities and the g and an values of Ar3Ge radicals... 

Calculated Spin-Density Distribution (p,) in Xylene Cation-Radicals and Determined Partial Factors ((p,) of Ring-Attack Rates for Nitrations of Neutral Isomeric Xylenes with Nitric Acid in Acetic Anhydride... 

Source Calculated spin-density distribution (p)—Feng, 1., Zheng, X., Zerner, M.C., 7. Org. 

In many cases, the theoretical and experimental results agree rather well. In other cases, there are discrepancies between the theoretical and experimental results. A review of the successes and failures of using DFT to calculate spin densities and hyperfine couplings of the primary radiation-induced free radicals observed in the nucleobases has recently appeared [58]. 

Related research has been reported by Elder and Worley (39), in which MNDO was used to examine the structure of coniferyl alcohol, and its corresponding phenolate anion and free radical. This method represents an improvement over the PPP method, in that MNDO is an all-electron technique, and performs geometry optimizations. It was found that the calculated spin densities and charge values for the reactive sites did not correlate quantitatively with observed bond frequency, but it was observed that positions with partial negative charge and positive spin densities are the positions through which the polymerization has been found to occur. 

Using a similar approach, Evans and co-workers obtained values of hsi = -1.50, kcsi = 0.55, 8 = 0.15 for a series of trimethylsilyl-substituted naphthalene radical anions based on a Q value of -26.1 49). For phenyltrimethylsilylacetylene radical anion, the values of the heteroatom parameters that gave the best fit of the Huckel calculated spin densities with experimental values, using a Q value of 28, were hs, = -1.3, and kCSi = 0.65 when a 8 value of 0.1 was assumed. A resulting C—Si 7r-bond order of about 0.3 is obtained 43). 

Table 2. Experimental and calculated spin densities of flavin semiquinones...

The radical anions of phosphafulvene (80) and dibenzophosphafillvene (81) were generated by electrochemical reduction and their EPR spectra recorded between 110 K and room temperature.213 Comparisons of calculated spin densities and charge distributions are presented along with experimental data. The radical anions of o-, m-, or p-thiobenzoate esters were generated by electro-reduction and found by their ESR spectra to be persistent.214... 

Sources. Calculated spin-density distribution (p,) from Feng et al. 1986 partial factors ([Pg.253]

At the CNDO/2 level Davies 50) has calculated spin densities for some fluorinated nitrobenzenes and shown that they follow the general pattern of hyperfine coupling constants. 

Based on the result of the calculation, we will discuss the ESR spectra using the calculated spin density. 

FIGURE 8.Ans.l Calculated spin densities for the ground state and the first excited state (2A2) of pentadienyl radical (bold numbers). The numbers in italics are those arising from the VBDFT(s) calculations. 

Recently, the spin density (p) localized on the cyano nitrogens, ethylene carbons, and cyano carbons in. i(mnt)2 1 were determined by Hoffman and co-workers (381) using a combination of ENDOR and ESEEM spectroscopies. These studies were important, in that they were able to quantify the extent of spin delocalization onto the olefinic carbon atoms. The [Ni(mnt)2]1 study was complimented by 19F ENDOR studies on [ X i (tfd) 211 which, when interpreted in the context of the [Ni(tds)2]1 data (389), allowed a detailed account of the ji spin delocalization partitioned on each atomic center of [Ni(mnt)2J1 and [Ni(tds)2 1 (381). The experimental and calculated spin densities for the... 

The discrepancies between experimental and theoretical results have been discussed in a recent review article [82], This article presents the success and failure of DFT to calculate spin densities and hyperfine couplings of more than twenty primary radiation induced radicals observed in the nucleobases. Several cases are presented here. 

The femperafure-dependenf linewidfhs of fhe ESR hfs of La Cs2, Sc C82 and Gd C82 have been discussed by Kato et al. (1993, 1995a,b, 1996) in terms of fhe spin-rofafion coupling interaction. Dinse and co-workers (Ruebsam et al., 1995,1996a,b) investigated temperature dependence of ESR line widths of La Cs2/ La C9o, and Sc Cs2 in different solvents and obtained irrformation on the nuclear quadrupole interactions in these metallofullerenes. Dunsch and co-workers (Bartl et al., 1994,1997 Seifert et al., 1998) studied Y satellite structures of M C82 (M = Sc, Y, La) in detail and reported that the manifold of hfc (hyperfine constants) could be interpreted by the calculated spin density distributions. 

Table IV. Calculated Spin Densities of Oxygen of H2O Ligands in P450 and...

Figure 8.27 (a) Chain of sites along the asymmetric oxygen direction taken from the PBE relaxed MoO3(010) surface with a terminal oxygen atom vacancy the structure of the perfect surface is overlaid as a line drawing, (b) As (a) for the PBE + U optimization, (c) The calculated spin density for the PBE + U calculation showing the full simulation cell for parts (a) and (b). 

The calculated spin densities of the two conformers support the conclusions derived from the bond lengths—most of the unpaired electron density is located on the tertiary cyclopropane carbon (Cl) and the terminal vinyl carbon (CjS). The general type of spin-density distribution calculated for the two conformers of 15 + has precedent in several vinylcyclopropane systems with locked geometries (vide infra) [134, 135]. 

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