Odd-electron bonds between other identical heteroatoms

4 Odd-electron bonds between other identical heteroatoms 

All of what has been described for sulfur-centered radicals and ions applies, in principle, to corresponding species with other heteroatoms as radical site. Whether it is three- or five-electron bonds, the basis of their establishment is always the interaction of a singly occupied orbital with a lone pair orbital and promotion of one of the electrons into the lowest lying antibonding orbital. The following gives a brief survey on examples with heteroatoms other than sulfur. 

In this context it is interesting that the reduction could not be achieved, however, with (CH3)2C 0H radicals despite an estimated overall exothermicity of the reaction. A substantial steric effect on the rate of electron transfer has been suspected. 

Analogues to the five-electron bonded 2a/27t/l7t disulfide radical cations in nitrogen-based systems, namely, hydrazine radical cations could be generated by one-electron reduction of trialkyl diazenium salts (eq. 49) and subsequent equilibration of the neutral product radical with its protonated form. The pK of the R=t-butyl substituted species, incidentally, is 7.0, 2.6 units below that of the parent hydrazine compound. The results emphasize the importance of structural parameters, in particular those which control orbital orientation and overlap. 46,147 Jhe alternative possibility to generate such 

Concerning other Group V elements, some low temperature (77 K) ESR radiation studies have verified the existence of 2c/lc radical cations with P.. P and As. . As bonds. 149,150 in solution, only one mention has been made, namely, on (Et3P. .PEt3) .15i. in this case assignment was made on the basis of a transient optical absorption at 385 nm obtained upon reaction of OH radicals with triethyl phosphine in pulse irradiated aqueous solution at pH 7. The high pH was necessary to prevent the phosphorus from protonation and keep the phosphorus lone pair available for both, one-electron oxidation and P-P orbital coupling. 

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