Highest spin

Hund s rules tell us that the lowest energy term of these is as it has the highest spin multiplicity (25 +1=3) and the highest value of L (3 for an F term). 

The only electronic states that can be treated are those that correspond to the highest spin multiplet of a given orbital configuration. 

For neutral radicals, the most significant term in eq. (144) is that which is first order in the overlap. This term contains expansion coefficients of directly interacting positions where in dimerization a new a bond is formed. The higher the values of these expansion coefficients, the larger is the interaction energy, in accord with chemical anticipation for dimerization to occur in positions of the highest spin densities. With radical ions, also, the last terms in eqs. (143) and (144) are important, since they stand for coidombic interactions. 

Substitution products of the carbon-bonded hydrogen were obtained. A synthesis of coenzyme Q, was achieved in this way (example 6, Table IV). The site of attack in quinones is highly specific and corresponds to the noncarbonyl ring site of highest spin density of the quinone radical anion (lOg, 127). 

SO on. The ground state is the state with the lowest energy. It contains the maximum number of unpaired electrons (highest spin multiplicity) and if more than one state has the same value for net spin (S), the ground state is that with the highest net orbital angular momentum (L). In addition, the total angular momentum quantum number is J = L -i- S if the shell is more than half-filled and J = L - S if not. 

Figure 6.5 The five possible structures of RCyo". Dots represent the carbons with the highest spin density, as calculated for the HCyo" isomers [45],...

The results of these studies show that little or no spin density occurs in the pyrimidine ring, but rather the unpaired spin distribution is concentrated in the pyrazine and benzenoid portions of the isoalloxazine ring (Table 2). The site of highest spin density is the N(5) position with substantial densities also occuring at C(8) and at N(10). From ESR studies of 4a enriched flavins. Walker et al. 

Table J Orbital configuration for the highest spin state of two, three, and four electrons belonging to each vp manifold...

The other point of interest relates to the nature of the highest spin state observed, that decaying by the 971 keV transition. If the 971 and 1031 keV lines are stretched E2 transitions, as we suspect, this state is the 46+ one that is the maximally aligned state predicted by theory and analogous to... 

Fleischmann et al s 34 report cyclic voltammetry data for the oxidation of a series of aromatic hydrocarbons in a molten salt electrolyte, AlCl3-NaCl-KCl at 150°. Electrooxidation in this medium occurs at unusually low oxidation potentials. Tris-(p-substituted phenyl)amines, with the exception of tri (p-nitrophenyl) amine, yield very stable radical cations by all electrochemical criteria 380>S42 Mono- and bis-p-substituted triphenylamines, however, dimerize with rate constants ranging from 101 to 10s M 1 sec 1 to benzidines 176 (Eq. (237)), which subsequently are oxidized to the radical cations 177, whose ESR-spectra are observed. Dimerization is fastest with the p-N02 andp-CN-derivative, in accordance with HMO calculations, which predict the highest spin sensity in the p-position of these compounds 542 ... 

Of the terms arising from a given configuration, the lowest in energy is the one having the highest spin multiplicity. 

The Orgel diagrams illustrated in figs 3.11 and 3.12 indicate that, for electronic transitions between crystal field states of highest spin-multiplicities, one absorption band only is expected in the spectra of 3d1,3d4,3d6 and 3d9 cations in octahedral coordination, whereas three bands should occur in the spectra of octahedrally coordinated 3d2, 3d3, 3d7 and 3d8 ions. Thus, if a crystal structure is known to contain cations in regular octahedral sites, the number and positions of absorption bands in a spectrum might be used to identify the presence and valence of a transition metal ion in these sites. However, this method of cation identification must be used with caution. Multiple and displaced absorption bands may occur in the spectra of transition metal ions situated in low-symmetry distorted coordination sites. 

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