Diamagnetic species

The intrinsic defects include paramagnetic and diamagnetic species (24,27,28). The paramagnetic defects have received the most study because they are readily detectable by electron spin resonance (esr) spectrometry. Paramagnetic defects that have been identified by esr include the center, 6i the... 

The proposed diamagnetic species include the neutral oxygen vacancy, 6i—S , the doubly coordinated siUcon, —O—Si—O— and the peroxyl bond,... 

A dication derived from 1,3,5,7-tetramethylcyclooctatetraene is formed at —78 C in SO2CI by reaction with SbFj. Both the proton and carbon NMR spectra indicate that the ion is a symmetrical, diamagnetic species, and the chemical shifts are consistent with an... 

The one-electron reduction of the Ni-C form results in the diamagnetic species Ni-R. From the redox titration studies of Lindahl s group, a plausible catalytic cycle can be postulated where the enzyme in the Ni-Sl state binds H2 (77) and becomes the two-electron more reduced Ni-R state. Sequential one-electron oxidations from Ni-R to Ni-C and then to Ni-Sl will close the cycle (Fig. 6). The various redox states differ not only in the extent of their reduction, but also in their protonation, as shown by the pH dependence of their redox potentials (87). It is remarkable that both EPR (which monitors the magnetic... 

As earlier mentioned, one of the reasons of the poor stability of gold(II) complexes is the unfavorable energy of the odd electron. The formation of a metal—metal bond in dinuclear gold(II) complexes giving diamagnetic species provides an extra stability. Thus, the number of... 

Co—0—0—Co. When this jU-superoxocobaloxime is reacted with relatively strong Lewis bases decomposition takes place to give a diamagnetic species and a paramagnetic oxygenated product. (Base Co—0—0). The ESR spectrum of this oxygenated product is strikingly similar to superoxocobalamin 115). 

Here there is no formal electronic bar to interaction between the electrons, i.e. pairing to form the diamagnetic species (137) but this does not in fact happen, because the bulky chlorine atoms in the o-positions prevent the benzene rings from attaining a conformation close enough to coplanarity to allow of sufficient p orbital overlap for electron-pairing to occur. 

O- species. Similarly, Che, Naccache, and Imelik (91) proposed that the electron donor centers are associated with OH- groups which are present on the surface following activation at temperatures below 350°. Again, it is difficult to devise a mechanism in which one obtains a single paramagnetic ion from two relatively immobile diamagnetic species. Obviously, the details for the formation of the radical cations and anions are not well understood. 

A paramagnetic species has one or more unpaired electrons and is drawn towards a magnetic field. A diamagnetic species has all electrons paired and is slightly repelled by a magnetic field. 

Recently, an NMR study of the diamagnetic species resulting from lithium reduction of 8 was reported. The THF solution revealed a single H NMR peak at 6.95 ppm, and three C NMR lines at 86.8, 95.1, and 112.4 ppm, indicating that the reduced species retains the high symmetry of neutral corannulene. Moreover, consideration of the C NMR chemical shift, as compared to neutral 8, provides a... 

It behaves, hardly surprisingly, very like PhjC- (cf. p. 300), existing out of solution as a colourless solid, but this latter is probably a polymer rather than a dimer as with PhjC. The solid is dissociated in solution to about the same extent as the Ph3C- dimer. The unpaired electrons in the biradical form (135) cannot interact with each other to form a wholly paired, diamagnetic species, as such interaction across both central benzene nuclei would necessitate m-quinoid forms that cannot exist the electrons are thus internally insulated from each other. Such internal insulation in biradicals may also arise through steric rather than electronic causes. Thus the species (136) exists in solution as a biradical to the extent of 17%, being in equilibrium with a polymer (like 135) ... 

This is a monomer unit associated in some manner with an electron giving a diamagnetic species. The Arnold and Patterson model, obtained from theoretical considerations, helps to reconcile the magnetic and conductance data of metal-ammonia solutions. 

The transverse relaxation rate enhancement / 2P could be treated in the same way if it were not for the difference in chemical shift A com between the paramagnetic and the diamagnetic species. As has already been shown, the difference in chemical shift causes a line broadening — an increasing in R2M — even when the... 

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