Efficiency of radical production

AIBN is, however, virtually unaffected by the presence of dithio-phosphates (Table II). Further, with specific reference to the oxidation of the disulfide in Table I, which has no effect on the rate of AIBN-initi-ated autoxidation of cumene (6), it is unlikely that the efficiency of radical production from AIBN increases since this would produce a prooxidant effect in cumene. Thus, the zinc salt inhibitor is being oxidized in competition with the main chain reaction. 

The ESR method is useful in two aspects for studies of photochemical processes involving paramagnetic species the qualitative mechanistic aspect and the quantitative rate measurement. For the mechanistic approach we have seen from Section IV how transient radicals can be observed during photolysis. The major disadvantages are (a) It is not practical to determine accurately the quantum efficiency of radical production. Thus the radical process evidenced by ESR can well have been a very minor photochemical process, due to the high sensitivity of the modern ESR spectrometer. (b) In static... 

Efficiency of radical production is threefold greater than from synthetic melanin produced by oxidation of 88... 

When the molecule concerned is a radical initiator this has implications for the efficiency of radical production, related to cage escape. Under supercritical conditions, geminate recombination can be controlled by density, as described earlier. 

The success of the multifunctional initiators in the preparation of block and graft copolymers depends critically on the kinetics and mechanism of radical production. In particular, the initiator efficiency, the susceptibility to and mechanism of transfer to initiator, and the relative stability of the various radical generating functions. Each of these factors has a substantial influence on the nature and homogeneity of the polymer formed. Features of the kinetics of polymerizations initiated by multifunctional initiators have been modeled by O Driscoll and Bevington 64 and Choi and Lei.265... 

Nada H, Oikawa K, Ohya-Nishiguchi H, Kamada H. Efficient hydroxyl radical production and their reactivity with ethanol in the presence of photoexcited semiconductors. Bull Chem Soc Jpn 1994 67 2031-2037. 

Obviously, the relative magnitudes of the rate constants for the two LHD reactions and of that for the cross-coupling of the two different radical anions will affect the efficiency of MHC production. Even for equal concentrations of the two radical anions, the three individual rate constants must be similar to result in the statistical distribution of MHC and LHD products. 

In the design of radical processes involving Lewis acids, all of the possible pathways and equilibria as well as the relative reactivity of species present in a reaction mixture must be considered. Within a given reaction mixture, products can be formed via uncomplexed mono- or bidentate pathways, and the complexes formed may be monomeric or polymeric. In stereoselective reactions, it is important to consider pathways leading not just to major products but also to minor products. Small changes in the efficiency of minor product formation can have a significant impact on product ratios. 

Allowing in the usual way for geminate recombination in the aqueous phase through an efficiency / (which is not the same as the efficiency for entry into a particle, which is considered later), the rate of radical production is given. by... 

For the efficient generation of annihilation ECL, three conditions should be met as follows (1) sufficient energy in the electron transfer reaction to produce the excited state for ECL emission, (2) stable radical ions of the precursor molecules in the electrolyte, and (3) good PL efficiency of a product of the electron transfer reaction. 

In fact not all radicals will initiate a polymeric chain some of the radicals are lost in side reactions (such as recombination of the initiator fragments). For this reason the efficiency factor / is introduced. / is the fraction of radicals that actually initiate a polymeric chain, the rate of radical production (leading to an actual initiation step) pi is then equal to ... 

The rate of initiation, which is the rate-controlling step in free-radical polymerization, is also related to the efficiency of the production of two radicals from each molecule of initiator, as shown in the following rate equation ... 

The extent of overlap of the absorption spectra of the oxygenate with the spectrum of wavelengths available in sunlight, as well as the quantum efficiencies of radical and molecular products formed from these hydrocarbon derivatives, determine... 

Styrene, the most efficient quencher of triplet excited states of carbonyl compounds among a great variety of olefins employed by Ausloos and Rebbert (1964), gave no detectable influence on the ethene and carbon monoxide quantum yields when 20.1 Torr was added to 19.9 Torr of 2,2-dimethyl-3-hexanone (Nicol and Calvert, 1967). However, an almost quantitative removal of radical products of 1-propyl and 2-methyl-2-propyl radicals resulted. Since 4>co was unaffected by styrene addition, the radical... 

---