Nitrogen centered radicals, chemistry

Although much of the chemistry of NO is dominated by the fact that it is a radical (discussed in Section III), it does not possess the type of reactivity normally associated with other radicals. For example, unlike other carbon, oxygen-, or nitrogen-centered radicals, NO does not even have the tendency to dimerize. That is, at standard temperature and pressure, NO tends to remain in the monomeric form. This lack of dimerization has been attributed to the fact that overall bonding does not increase when two NO molecules interact (Ragsdale, 1973). Thus, the formal bond order in NO is 2.5, while the bond order for ONNO is 5. 

The chemistry of nitrogen-centered radicals has been reviewed comprehensively by Nelsen (X), and, more recently, by Forrester (2 ). The present paper deals largely with the chemistry of a more restricted group of these radicals, the dialkyl-amino radicals. 

The chemistries of nitrogen-centered and sulfur-centered radicals have been reviewed in detail (Alfassi 1997, 1999), and here only some aspects can be discussed that seem pertinent to the formation, reactions and repair of DNA radicals. 

In stark contrast to azoalkanes, azoxy compounds rarely form radicals on heating or irradiation. Furthermore, they are unreactive to alkyl radical attack unless the reaction is intramolecular. For example, P-carbon centered radicals cyclize to azoxy nitrogen or oxygen and produce short-lived aminyl nitroxides that reopen or hydrazyl radicals that undergo fragmentation. The azoxy group is a powerful stabilizer of an adjacent radical center but the chemistry of a-azoxy radicals (hydrazonyloxides) and their dimers is not fully understood. 

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