Tetra-atomic radicals

It has proved convenient to classify centers other than trapped electrons as monatomic, diatomic, triatomic, tetra-atomic and penta-atomic (9), these classes being expanded to include more complex species having similar basic structures. Thus, the radicals R2NO and (S03)2N02 were classed with the corresponding simple AB3 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. 

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

If the same alkyl group occurs more than once as a side chain, this is indicated by the prefixes di-, tri-, tetra-, etc. Side chains are cited in alphabetical order (before insertion of any multiplying prefix). The name of a complex radical (side chain) is considered to begin with the first letter of its complete name. Where names of complex radicals are composed of identical words, priority for citation is given to that radical which contains the lowest-numbered locant at the first cited point of difference in the radical. If two or more side chains are in equivalent positions, the one to be assigned the lowest-numbered locant is that cited first in the name. The complete expression for the side chain may be enclosed in parentheses for clarity or the carbon atoms in side chains may be indicated by primed locants. 

Specifically, the reaction of trifluoromethyl radicals with carbon tetra-iodide produces perfluoro-tert-butyl iodide and perfluoroneopentane in the ratio of 3 1. Incomplete substitution is presumably due to steric factors around the crowded, central carbon atom. 

In a chain reaction, the step that determines what the product will be is most often an abstraction step. What is abstracted by a free radical is almost never a tetra- or tervalent atom (except in strained systems, see p. 989) and seldom a divalent one. Nearly always it is univalent, and so, for organic compounds, it is hydrogen or halogen. For example, a reaction between a chlorine atom and ethane gives an ethyl radical, not a hydrogen atom ... 

Star polymers are a class of polymers with interesting rheological and physical properties. The tetra-functionalized adamantane cores (adamantyls) have been employed as initiators in the atom transfer radical polymerization (ATRP) method applied to styrene and various acrylate monomers (see Fig. 21). 

The isomerization shown in Scheme 6.32 involves two intermediary dianions and not the direct conversion of the initial anion-radical into the final one. However, what is the driving force for this isomerization The molecule of l,3,6,8-tetra(tcrt-butyl)naphthalene is nonplanar the tert-butyl group and carbon atom at position 1 of the naphthalene skeleton lie off the plane of the molecule. The corresponding anion-radical has the same stereochemical peculiarity (Goldberg 1973). Such bending removes the steric strain but, naturally, decreases the degree of the n-electron delocalization over the neutral molecule. As for the anion-radical, its unpaired electron delocalizes less effectively than the anion-radical of the unsubstituted naphthalene. Bending of the naphthalene skeleton... 

Removal of an electron from a hydrazine unit changes the lone pair orbital occupancy from four to three, which has a large effect on the preferred geometry with respect to the nitrogens. The formation of a three-electron bond has also been demonstrated in the cation radical of octamethyl-l,2,4,5-tetra-aza-3,6-disilacyclohexane. In this cation radical, the spin density is distributed between only two of the four nitrogen atoms. There is a pronounced interaction of the unpaired electron with protons of the methyl groups joined to these two nitrogen atoms. 

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