Transfer spin density

The case of the hexa(pyridine) nickel(II) complex has been extensively debated in the early literature of NMR of paramagnetic complexes [17-21]. The shift pattern with a-H > y-H > (i-H (Fig. 2.11 and Table 2.3) was soon recognized to be predominantly of a-type. The ligand has a a MO system which has the correct symmetry to overlap with the dx2 y2 and dz2 orbitals. However, spin polarization can induce V2 spin density in the it system. Once some unpaired spin density is in a p orbital, it spin-polarizes the electrons of the C—H a bond, thus producing a further mechanism for transferring spin density on the proton. The proton A/h value from this mechanism is proportional to the spin density on the carbon pz orbital, p , through a proportionality constant >ch ... 

Keywords Source function Electron density Electron spin density Chemical bonding Electron conjugation Aromaticity Non-planar aromatic frameworks Chemical transferability Spin density transferabilily... 

The crystal and molecular structure of the 44, 45, and C5-vinylferro-cenyl-thymidine show that the substituted cyclopentadienyl ring is essentially co-planar with the nucleobase (164). DFT calculations indicate that, irrespective of the extent of saturation in the bridging C2-unit in ethynyl-, vinyl- or ethyl-ferrocenyl-C5-thymidine, a similar amount of spin density is transferred to the nucleobase (Fig. 48). The reduction potentials for these compounds are shifted little compared to the parent ferrocenyl derivatives. 

Figure 3. CuCl2(NITPh)2,2 projection of the spin density along the n direction of the nitroxide. Contours 5 n(10) mpi/Al Coordination of a nitroxide to a copper(II) ion results in spin density transfer from the bound O atom to the N atom.

We propose that the first step in the formation of quinones, as shown in Scheme 3 for BP, involves an electron transfer from the hydrocarbon to the activated cytochrome P-450-iron-oxygen complex. The generate nucleophilic oxygen atom of this complex would react at C-6 of BP in which the positive charge is appreciably localized. The 6-oxy-BP radical formed would then dissociate to leave the iron of cytochrome P-450 in the normal ferric state. Autoxidation of the 6-oxy-BP radical in which the spin density is localized mainly on the oxygen, C-l, C-3 and C-12 (19,20) would produce the three BP diones. 

While the rate of an electron-transfer process and thus the mode of the resulting spin-density distribution can be controlled by the length and the conformation of the spacer groups, the ion pairing creates an additional factor that can serve as some external control even for a given choice of subunits and spacers. 

The rate of degenerate intramolecular electron-transfer processes in biselectrophoric redox systems, and the observed spin-density distribution over one or two units depend upon the overall reorganization energy and thus upon... 

The scission product from the diamagnetic [Ga(BPG)(DTBC)] complex is considerably less (4%) than that from the corresponding Fe complex (97%) (29). Gallium(III) is a diamagnetic d10 ion with an ionic radius very similar to that of iron(III) and expected to possess similar Lewis properties to that of Fe(III). Thus, the results clearly demonstrate that the ability of the metal center to transfer paramagnetic spin density to... 

These generalized Fukui functions are local reactivity indexes, as they depend on the coordinates r where they are determined, in other words their values vary from one point to another within the molecule. It is clear that these quantities can be used to know how the charge or (and) spin densities respond when there are charge or (and) spin transfer to the reacting molecule. 

Magnetization transfer (MT) techniques provide additional information on the composition of tissues, which cannot be achieved by methods exclusively based on spin density, relaxation behaviour, or the chemical shift of the signals. The... 

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