Primary- radicals definition

The definition of an antioxidant suggests a functional assay of antioxidants by measuring inhibition of appropriate (easy to study) oxidation reactions. Such assays can be called inhibition assays for antioxidants (Fig. 2). Various oxidants are used in TAC assays. In many cases, thermal decomposition of 2,2 -azobis (2-amidopropane) (ABAP) is the source of oxidizing radicals. ABAP undergoes temperature-dependent homolysis. The primary radicals produced by thermal decomposition of the initiator react with oxygen to produce peroxyl and alkoxyl radicals, which are oxidizing species in the system (Fig. 3). The amount of free radicals formed in an aqueous medium by decomposition of ABAP at pH 7.4 and at 37°C equals 1.36 x 10-6 [ABAP] x t, where t is time in seconds and [ABAP] is in mol L-1 (N8). 

Some quantum yields of radical polymerization (< >p for definition see Eq. (2b)) with the model monomer MM A are presented in Table 5. It is obvious that a variety of parameters acts on this value. Mainly, the participation of initiator molecules and of primary radicals on chain termination are responsible for the differences in the < >p-values. 

The kinetic chain length, v, is defined as the average number of monomers consumed by each primary radical. Obviously from this definition, the magnitude of the kinetic chain length will depend on the rate of the propagation relative to the termination rate, i.e.. 

When characterizing polymer networks, the following definitions are typically applied [150] and are illustrated in Fig. 7. When a radical on a polymer chain propagates through a pendant double (i.e. a double bond from a monomer with one double bond already reacted), a crosslink, secondary cycle, or primary cycle can be formed. A crosslink forms when the radical reacts with a pendant... 

Time-resolved CIDEP and optical emission studies provide further definitive characterization of the triplet and excited singlet states followed by their primary photochemical reactions producing transient radicals in individual mechanistic steps in the photolysis of a-guaiacoxylacetoveratrone. Both fluorescence and phosphorescence are observed and CIDEP measurements confirm the mainly n,n character of the lowest triplet state. The results indicate a photo triplet mechanism involving the formation of the ketyl radical prior to the P-ether cleavage to form phenacyl radicals and phenols. Indirect evidence of excited singlet photo decomposition mechanism is observed in the photolysis at 77 K. 

Deoxygenation of ROH. Acetates, primary, secondary, or tertiary, are deox-> genated when heated with 1 in the presence of a radical initiator, di-r-butyl peroxide (DTBP). Yields using (C6H5)3SiH in place of 1 are definitely lower. The presence of a double bond in the substrate can lower yields owing possibly to hydrosilylation. 

The present observations could well be explained on the same basis since hexamethylcyclotrisiloxane polymerizes via both anionic and cationic mechanisms (5). (No evidence exists to date for free radical polymerizations.) The greater activity of H2O as an inhibitor, as compared with NH3, is explained on the basis of a more rapid ion transfer. Since this would be a hydrogen ion rather than a hydride ion, it further suggests an anion as the primary polymerization species in the present polymerization. The authors feel, however, that further work is required before definite conclusions can be drawn regarding the polymerization mechanism or mechanisms. 

An explanation for the increasing concentrations of CH4 is not quantitatively definitive with the present state of knowledge. The primary atmospheric destruction processes for CH4 and CO are certainly through reactions (6) and (10), but the chief removal processes for HO radicals are the same two reactions (6) and (10), while the eventual further... 

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