Nitrogen-centered radicals stability

The stability of heteroatom-centered radicals can be defined relative to reference systems sharing the same type of radical center. The stability of nitrogen-centered radicals may, for example, be defined relative to ammonia... 

Table 5 Radical stabilization energies (in kj/mol) of nitrogen-centered radicals at 0 K according to Eq. 3... 

Studies on the structure of the enzyme-bound adduct revealed additional information as to the mechanism of inactivation and strengthened the proposals put forth concerning the oxidation of substrates and inhibitors through a nitrogen-centered radical intermediate. The stability of the covalent adduct formed following MAO inactivation by A-cyclopropylbenzylamine, A-cyclo-propyl-a-methylamine, and a,a-dimethylbenzylamine was found to depend on... 

In carbonate solution, inhibition from CO in the Ce(IV) oxidation of semicarbazones " suggests participation of a [Ce(IV)-semicarbazone] intermediate complex. With acetone-semicarbazone, this complex has a stability constant of 13.4 and decays with a specific rate of 23.8 x 10 " s to give a nitrogen-centered radical. 

Such strong inward pyramidalization of the nitrogen atoms is stabilized by the overlapping of the nitrogen electrons forming a three-electron two-center bond in the cation-radical discussed in... 

Stabilization Energies of Nitrogen-Centered Free 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. 

Initiators that have been utilized to initiate styrene polymerization can be generally categorized into three types peroxides, azo, and carbon—carbon (177). Peroxides are thermally unstable and decompose by homolysis of the 0—0 bond, resulting in the formation of two oxy radicals. Azo compoimds decompose by concerted homolysis of the N—C bonds on either side of the azo linkage, resulting in extrusion of nitrogen gas and the formation of two carbon-centered radicals. Carbon-carbon initiators decompose by homolysis of a sterically strained C—C bond, resulting in the formation of two carbon-centered radicals. The radicals initiate styrene polymerization and end up attached to the chain ends and may have an effect upon polymer stability (178-181). 

---