Anions dianions

Fig. 22. ESR spectra of the radical anion, dianion and radical trianion of 2.4.6-triphenyl- -phosphorin...

X -phosphorins have physical properties which are rather similar to those of pyridines. But the chemistry of X -phosphorins is very different, due mainly to the phosphorus atom which can easily lose one electron to produce a stable radical cation, or accept one or more electrons to yield a radical anion, dianion or radical trianion. Nucleophiles add to stable X -phosphorin anions. In contrast to pyridine chemistry, no stable X -phosphorinium compound (corresponding to a N-alkyl-pyridinium salt) could be isolated. Instead the electron shell of phosphorus is enlarged by addition of an electrophile yielding a X -phosphorine derivative. 

Analysis of the electron density indicates the presence of a large number of different interactions between the atoms of the inner part of the systems considered, for instance, chalcogenic interactions between sulfur (or selenium) and the opposed N atom anion. Special emphasis was put on acid-base equilibria (neutral/anion/ dianion). The relationship between the electron density and the Laplacian at the bcp indicate that these interactions are similar to those encountered in intermolecular interactions, to the point that they can be analyzed together. 

Additional information about the electrochemical behaviour of pyrimidone-2 is furnished by studies in non-aqueous medium, (CH3)2SO, with particular attention to the possible role of free radicals and anionic species (radical anions, dianions, dissociated conjugated bases) as reaction intermediates82). 

We have seen that aromatic stabilization leads to unusually stable hydrocarbon anions such as the cyclopentadienyl anion. Dianions of hydrocarbons are rare and are usually... 

Spectral data recorded in this table have been selected from the literature in the preferred order of the pure species (0, neutral, +, cation ++, dication anion —, dianion) in aqueous solution at specific pH (or // ) values, and solutions in cyclohexane (CjH, j), alcohols, and other solvents. Published (nm) and log e values are quoted, except that some values have been estimated from the spectral curves. The letters cv in the table indicate the existence of a published spectral curve. Values in italics refer to shoulders and inflections. 

II. FORMATION OF RADICAL ANIONS, DIANIONS, AND POLYANIONS A. Experimental Aspects... 

The first step in a one-electron transfer process is the formation of the respective radical anion. Local spin density distributions in radical ions can be obtained from the ESR spectrum 54 55>. The estimation of rc-charge densities is based on the assumption that the doubly occupied M.O. of a diamagnetic anion (dianion or tetraanion) is the same as the singly occupied M.O. in the respective radical-anion. They belong to the same point group symmetry. Based on this assumption it is concluded that the spin density of a radical-anion enables the prediction of the rc-charge density of a dianion. 

A series of mononuclear octahedral thiomolybdenyl derivatives [MoX2(Tp )S] (X, X2 = anion, dianion) has been synthesized and characterized by Young and coworkers.99 These complexes provide insights into the electronic nature and chemistry of the catalytically and biologically important thiomolybdenyl units.99... 

SZWARC Electron Affinities of Radical Anions ( Dianions... 

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