Radicals n-propyl

Because the starting material (propane) and one of the products (H ) are the same m both processes the difference m bond dissociation energies is equal to the energy dif ference between an n propyl radical (primary) and an isopropyl radical (secondary) As depicted m Figure 4 20 the secondary radical is 13 kJ/mol (3 kcal/mol) more stable than the primary radical... 

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). 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

Above 300°C. the effective reaction of an alkyl radical with oxygen may be Reaction 3 rather than 2 because of the reversibility of Reaction 2. If it is assumed that Reaction 3 is important at about 450°C., its rate can be estimated from the competition between pyrolysis and oxidation of alkyl radicals. Falconer and Knox (21) observed that the ratio of (pro-pene)/(ethylene) from the oxidation of propane between 435° and 475°C. increased with oxygen concentration and decreased with temperature—the apparent activation energy difference for the two reactions forming the olefins being 27 =t 5 kcal. per mole. They interpreted this result in terms of a competition between Reactions 1 and 3. The observed ratio (propene)/(ethylene) was 3.5 at 435°C. and 10 mm. of Hg pressure. If log ki(propyl) = 13.2 — 30,000/2.30RT, the value for the n-propyl radical (34), then log k3 = 8.0. If the A factor is 109-3, we derive the Arrhenius equation... 

The formation of the n-propyl radical from propylene suggests that this hydrogen transfer should proceed through some energetic process caused by silent discharge because a normal hydrogen atom addition to propylene proceeds almost exclusively to the terminal carbon (15). Thus, two molecular processes similar to those in the reactions of cyclohexene may be plausible to interpret the hydrogen transfer. 

On the other hand, in a similar study recently carried out by Falconer et al. (41), no evidence was found for the presence of allyl radicals and the occurrence of reaction (23) appears unlikely. The products could be explained by assuming initial formation of hot iso- and n-propyl radicals. As will be discussed in the next section, 94% of iso- and 6% of propyl radicals are formed in this reaction. The further fate of both these radicals has to be considered, since hot n-propyl decomposes readily into C2H4 and CH3 but the same is not true for iso-propyl, where a simultaneous internal migration of an H atom must occur. 

Falconer et al. studied the reactions of H atoms with C3H6 and C3D6 as a function of hydrogen pressure and determined the rates of decomposition (relative to stabilization) of the hot radicals. In the case of n-propyl radicals these rates (fc ) were compared with the calculated theoretical values. The data are summarized in Table VI, where... 

Falconer and Cvetanovic (40) attempted to obtain a more quantitative value for the fraction of nonterminal addition in the case of propylene. They produced hydrogen atoms by mercury photosensitized decomposition of H2, using at least 100 times as much H2 as C3H6 and total pressures of 40 and of 250 mm. Under these conditions the reactions of importance were the combination and disproportionation of the iso- and n-propyl radicals and their cross reactions, the combination of the two radicals with H atoms (assumed to be equally probable), and a very small amount of decomposition of hot n-propyl radicals. Disproportionation to combination ratios were taken as 1.64 for two iso-propyl, 1.14 for two w-propyl, and hence 1.39 was taken as the mean of the two values for one iso- and one n-propyl radical. Using these values and the analysis of the products, the nonterminal addition of H atoms to C3H6 and C3D6 was found to amount to 6 1%. 

The Relative Rates and the Percentage of n-Propyl Radicals Initially Formed in the Reaction of Hg 6( 3P,) Atoms with Propane and the Deuterated Propanes11... 

Fig. 23. Yield of n-propyl radicals as a function of added 1-butene in the mercury-photosensitized decomposition of propane. —C3D8 O—C3Ha (2 mole-% NO).

This explanation is similar to one given by Bolton and Carrington (1962) for the fine-width alternation found for durosemiquinone, but is in contrast with that proposed to explain the remarkable alternation found for n-propyl radicals trapped in solid argon (Cochran et al., 1961). In this case, as discussed in Section VI, A, the broadening effect is... 

Fig. 2. Plot of the log of the rate constants for addition of heptafluoro-n-propyl radical to some alkenes the ionization potentials of the alkenes...

Refers to the average energy of the formed n-propyl radicals above 0 (31>0 kcal.) for decomposition to CHa and C3H4. 

Cyclobutylamide, N-lithio-N-propyl, radicals from and fate of, 58, 6 Cyclobutyliminyl radicals, generation, cleavage, 58, 18... 

The e.s.r. spectrum of a deposit formed by the deposition of hydrogen atoms on propylene in a matrix of adamantane is shown in Fig. 18. Comparison with the spectra of the two possible product radicals, n-propyl and isoprop3d, shows clearly that addition has occurred almost exclusively to the terminal CH2-group to form the isopropyl radical. The possibility that a small amount of n-propyl radical is present cannot be ruled out, but from an analysis of the e.s.r. spectrum it is conservatively 3... 

Fig. 18. First derivative e.s.r. spectra in adamantane of (a) isopropyl radical, (b) radical formed by addition of H-atoms to propene, and (c) n-propyl radical.

These radicals decompose according to the /3-scission rule, which implies that the bond that will break is one position removed from the radical site, so that an olefin can form without a hydrogen shift. Thus the isopropyl radical gives propene and a H atom, while the n-propyl radical gives ethene and a methyl radical. The j9-scission rule states that when there is a choice between a CC single bond and a CH bond, the CC bond is normally the one that breaks because it is weaker than the CH bond. Even though there are six primary CH bonds in propane and these are somewhat more tightly bound than the two secondary ones, one finds substantially more ethene than propene as an intermediate in the oxidation process. The experimental results [12] shown in Fig. 10 verify this conclusion. Hie same experimental effort found the olefin trends shown in Table 2. Note that it is possible to estimate the order reported from the principles just described. 

The results listed in Table 19 have been determined by methods analogous to those used to study methyl and ethyl H-abstraction reactions. The yields of the abstraction product, propane or cyclopropane, must be corrected for the disproportionation reaction. The reference reaction is the radical combination reaction. For n-propyl radical reactions TABLE 20... 

Metathetical reactions of perfluoro-n-propyl radicals transfer of hydrogen atoms n-C3F7 + RH n-CsF H + R... 

The initiating mechanism of the cyclopropane-hydrogen reaction presumably results in an adsorbed n-propyl radical, while by reason of its weaker secondary C—H bond, propane probably dissociates into an isopropyl radical and an H atom. The close similarity between the distributions in the two cases su ested that exchange proceeds through the equilibria... 

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