Radicals table

In agreement with the theory of polarized radicals, the presence of substituents on heteroaromatic free radicals can slightly affect their polarity. Both 4- and 5-substituted thiazol-2-yl radicals have been generated in aromatic solvents by thermal decomposition of the diazoamino derivative resulting from the reaction of isoamyl nitrite on the corresponding 2-aminothiazole (250,416-418). Introduction in 5-position of electron-withdrawing substituents slightly enhances the electrophilic character of thiazol-2-yl radicals (Table 1-57). 

Affinities toward other alkyl radicals have also been measured by Szwarc and his co-workers using techniques similar to those described above, It is interesting to compare the affinities of naphthalene with those of quinoline toward methyl, ethyl, and n-propyl radicals (Table X). 

The pathways whereby oxygen-centered radicals interact with monomers show marked dependence on the structure of the radical (Table 3.8). For example, with MMA the proportion of tail addition varies from 66% for f-butoxy to 99% for isopropoxycarbonyloxy radical. The reactions of oxygen-centered radicals are discussed in detail in the following sections. 

Because of the importance of hydroperoxy radicals in autoxidation processes, their reactions with hydrocarbons arc well known. However, reactions with monomers have not been widely studied. Absolute rate constants for addition to common monomers are in the range 0.09-3 M"1 s"1 at 40 °C. These are substantially lower than kL for other oxygen-centered radicals (Table 3.7). 454... 

Transition metal salts trap carbon-centered radicals by electron transfer or by ligand transfer. These reagents often show high specificity for reaction with specific radicals and the rates of trapping may be correlated with the nucleophilicity of the radical (Table 5.6). For example, PS radicals are much more reactive towards ferric chloride than acrylic propagating species."07... 

The total yield of sulfinic acid from the mixed sulfoxides is higher than that from diphenyl sulfoxides (31%) but lower than that from the corresponding dialkyl sulfoxides, and accounts for about 45% of the OH radicals (Table 1). 

Dissociation energies D values) of R—H bonds provide a measure of the relative inherent stability of free radicals Table 5.4 lists such values. The higher the D value, the less stable the radical. Bond dissociation energies have also been reported for the C—H bond of alkenes and dienes and for the C—H bond in radical precursors XYC—H, where X,Y can be H, alkyl, COOR, COR, SR, CN, NO2, and so... 

Until now, applications of semiempirical all-valence-electron methods have been rare, although the experimental data for a series of alkyl radicals are available (108,109). In Figure 9, we present the theoretical values of ionization potentials calculated (68) for formyl radical by the CNDO version of Del Bene and Jaffe (110), which is superior to the standard CNDO/2 method in estimation of ionization potentials of closed-shell systems (111). The first ionization potential is seen, in Figure 9, to agree fairly well with the experimental value. Similarly, good results were also obtained (113) with some other radicals (Table VII). 

Tervalent organophosphorus compounds containing one single P-N bond with the valency of each atom saturated by protons or carbons (but no other heteroatoms) have been known since their discovery by MichaeUs more than one century ago [ 1 ] and named indistinctly as aminophosphanes, phosphanamines, phosphazanes, or phosphinous amides. This last chemical nomenclature is the one used by the Chemical Abstracts Service (CAS) for indexing these compounds and is also the one that best delimits the scope of this review those species derived from the parent H2P-NH2 (phosphinous amide in CAS nomenclature) by partial or total substitution of protons by hydrocarbon radicals (Table 1). 

The substituent effects predicted for vinyl radicals are rather similar to those already observed for alkyl radicals (Table 4). Attachment of alkyl groups or it systems to the radical center stabilize the radical while the introduction of a-acceptors in the a- or / -position are destabilizing. The nature of the... 

The results presented in Table 6.21 show that the good correlation between calculated and experimental barriers observed for the addition of the individual radicals (Tables 6.15 - 6.20) deteriorates significantly when the radicals are examined together. Further work is in progress to try to understand this variation in performance. The largest deviations from experiment are rather larger than desirable (LD ranging from -11.0 to +16.6 kJ/mol). 

Contrary to the general impression, phenol and aniline are poor retarders even toward highly reactive radicals such as the poly(vinyl acetate)-propagating radical (Table 3-8). Phenols with electron-donating groups (and, to some extent, similarly substituted anilines)... 

A comparison of the temperature behavior of various RCgQ radicals shows that the dimer bond strength depends on the size of the entering radical (Table 6.1). 

This reorganizational energy, the A energies deduced from experimental enthalpies [248], and the energies of the alkyl radicals (Table 12.3) now give the following... 

Still open also is the problem of para-products formation. Practically all comparable data are given in Table II. They exhibit a surprising independence of yields of para-product (63) from the polarity of the solvent. The not-too-convincing explanation that both Path A and Path B are equally participating in para-product formation is at hand. It is clear that more quantitative data are necessary to elucidate this problem. Experimentally found spin densities of photoexcited phenoxy radicals (Table III) would allow a preferential recombination of radicals in the para-position (cf. Eqs. 67 + 68 -> 73). 

Once again it would be extremely difficult if not impossible to account for such large A factors in terms of the relatively tight 4-center transition state of reaction H for which if anything a very small A factor of the order of 106 to 10 liter/mole-sec. might be expected. Compared to the H-abstraction reactions of radicals (Tables I and II) for which A = 108-5 liter/mole-sec., the value A = 10 2 is high by about 103-6. 

Radical attack on the central bond in [1.1.1 [propellane 1 occurs 2-3 times faster than attack on styrene96 and yields bridgehead bicyclo[l.l.l]pent-l-yl radicals6. Laser flash photolysis techniques were used to measure the rate constants for the reactions of la with five different radicals (Table 12)96"99. The addition of the phenylthiyl radical to la is... 

The second-order rate constant of H with common radical scavengers is relatively small. However, it is large enough to account for the removal of organic compounds. The high-energy electron beam process is the only process that produces these radicals. Table 12.3 summarizes the reaction rate constants of major organic pollutants with OH, eacf, and H. 

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