Some Tetra-Atomic Radicals

The isoelectronic radicals NO3 and CO with 23 valence-shell electrons, are predicted to be planar . Their standard Lewis stractures are of types (34) and (35) 

In contrast, the radicals NO, , PO, , SO, and CIO, with 25 valence shell electrons, have been foimd to have their odd electron delocalized over all atomic centres. For these radicals, Pauling 3-electron bonds may be developed without reducing the munber of A-0 (with A = P, S or Cl) bonding electrons. Thus we may write 

As is the case for ClOj (Section 6-3), the possibility exists that sulphur and chlorine 3d orbitals may participate appreciably in bonding for SO, and CIO,. If this occurs, the resulting valence-bond structures of types (43) and (44) 

Chapter 6 Pauling 3-Electron Bonds , 5-Electron 3-Centre Bonding. .. 

Using CIO2 as the example, the Addendum 2014 provides an alternative, non d-orbital approach that can be used to reduce the magnitudes of the atomic formal charges of valence-bond structures (30), (31), (41) and (42) for CIO2, CIO3 and SOi. 

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Electron 3-Centre Bonding and Some Tetra-Atomic Radicals... 

This is a 19-electron radical and can be contrasted with the radical N4, a 21-electron radical, which is thought to have a distorted square-planar structure, with all the nitrogen atoms equivalent (81). Another center, with four equivalent sulfur atoms, has recently been described, although details are not given (37). A square-planar structure again seems possible and it would be of interest to discover the nature of the orbital of the unpaired electron. Certainly the factors which determine the most stable geometry of these tetra-atomic radicals are a matter of some interest. 

There are a number of prefixes that show the number of particular atoms or radicals contained in a compound. Some of the most common are di and bi, meaning 2 tri, meaning 3 tetra, meaning 4 and pent, meaning 5. Thus, ammonium dichromate indicates the presence of 2 chromate radicals and sodium tetraborate the presence of 4 borate radicals. 

In some cases, it is possible to use cyclohexane as the hydrogen atom source in a chain process. This is illustrated by the efficient synthesis of tetra-O-acetyl-2-deoxy-D-glucose pictured in Scheme 17 [33]. The intermediate radical 11 arising from the... 

Electrochemical methods have played an important role in the recognition of cation radicals as intermediates in organic chemistry and in the study of their properties. An electrode is fundamentally an electron-transfer agent so that, given the proper solvent system, anodic oxidation allows formation of the cation radical without any associated proton or other atom transfer and without the formation of a reduced form in the immediate vicinity of the cation radical. Moreover, because the potential of the electrode can be adjusted precisely, its oxidizing power can be controlled, and further oxidation of the cation radical can often be avoided. Finally, the electrochemical experiment can involve both production of the cation radical and an analysis of its behavior, so that information about the thermodynamics of its formation and the kinetics of its reaction can be obtained, even if the cation radical lifetime is as short as a few milliseconds. There are some limitations, however, in the anodic production of cation radicals. The choice of solvent is limited to those that show reasonable conductivity with a supporting electrolyte (e.g. tetra-n-butylammonium perchlorate, TBAP). Acetonitrile, methylene chloride and nitrobenzene have been employed as solvents, but other favorites, such as benzene and cyclohexane, cannot be used. The relatively high dielectric constant of the suitable... 

Full details (see Vol. 1, p. 185) of the Japanese work on the preparation of trifluoromethylarenes from trifluoroiodomethane and iodoarenes in the presence of copper powder and a dipolar aprotic solvent have become available, and it appears that the best solvent in some cases is pyridine. This method (but with DMF as solvent) has also been used to prepare the compounds PhR [R = Me03C (CF3)3, CF3 0 (CF2)2, or perfluoro-2-tetra-hydrofurfuryl] in good yields from iodobenzene and the corresponding polyfluoroiodo-compounds. Perfluoroalkyl-copper compounds are very probably involved in such reactions, and the reactions of preformed n-perfluoroheptylcopper in dimethyl sulphoxide with the aromatic carbon-hydrogen bonds of benzene, toluene, p-xylene, nitrobenzene, and chlorobenzene also lead to (perfluoroalkyl)arenes (some replacement of chlorine occurs in the case of chlorobenzene). Homolytic substitution by perfluoro-heptyl radicals, perhaps within the co-ordination sphere of the copper atom,... 

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