Propyl radicals, abstraction reactions

CH3)2CDOH it is slowed by a factor of ca 5. This confirms that the primary reaction of 3BA with isopropyl alcohol is abstraction of the methine hydrogen to give BAH, which is observed spectroscopically, and the 2-hydroxy-2-propyl radical. These radicals combine and disproportionate to form the stable products. 

The explanation for the slow decrease in methanol is the same as for formaldehyde. The dramatic increase in the yields of ethyl and propyl alcohols at the pic darret clearly indicate the importance of abstraction reactions of the type above and of the appearance of alkoxy radicals at this point in the reaction. 

The Hammond Postulate applies only if both forward reactions are fast. Obtain energies for the transition states leading to 1 -propyl and 2-propyl radicals (propane+F end andpropane+F center). Draw an energy diagram for each hydrogen abstraction reaction (place the diagrams on the same axes). Do these diagrams indicate that use of the Hammond Postulate is justified Calculate the barrier for each reaction, and calculate the relative concentrations of 1-propyl and 2-propyl radicals that would form at 298 K if each reaction were irreversible. Use equation (2). How does this (kinetic) ratio compare to the equilibrium (thermodynamic) ratio of these radicals ... 

Von Bunau and Kuhnert calculated from the effect of additives that in the gas phase about 95 % of the hydrogen atoms formed in the radiolysis produced propyl radicals in this reaction while only 5% of the hydrogen atoms abstract hydrogen to form H2 and cyclopropyl radicals (equation 7) ... 

Only about 3wt% of ethane is observed in the steam cracking products, indicating that the formation of ethylene is the preferential fate of ethyl radicals. Note that most of ethane is formed via ethyl radical H-abstraction reactions, while less than 10% is due to the recombination reaction of methyl radicals. Similarly, propane formation is mostly due to the H-abstraction reactions of propyl radicals and only marginally to the recombination of methyl and ethyl radicals. 

Due to the regular branched structure of this isomer, linear 1-alkenes heavier than 1-heptene are not present and the relative amount of propyl and butyl radicals is significantly different too. In other words, the lumped H-abstraction reaction of a single model component loses the variety of primary products obtained from the previous lumped A0C15. It seems relevant to observe that to improve ethylene selectivity prediction, alkene components heavier than hexenes can be conveniently described with two different species, respectively corresponding to the true component 1-C H2 and to a lumped mixture of the remaining normal and branched isomers. 

Data listed in Table 19 for H-abstraction reactions of propyl radicals (n-propyl, isopropyl and cyclopropyl) have been recalculated from the original resulte on the basis of log(fe/l mole sec ) = 8.6 for the auto-combination reactions of all three radicals. This is in keeping with the recent experimental rate coefficients for isopropyl combination [264] and for ethyl combination [248, 250]. 

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... 

Following the pattern of H-abstraction reactions of the lower alkyl radicals, methyl to propyl, the analogous reactions of butyl radicals have been studied relative to the radical combination reactions. Unfortunately, the values of the rate coefficients of these combination reactions are by no means certain. Recent measurements of the combination reaction of... 

Methylcorrinoids are competent for the efficient methylation of alkyl radicals. Thermolysis of 2 -bis(ethoxycarbonyl)propylcobalamin and methylcobalamin at 70 °C led to formation of cob(II)alamin and the organic products 2-ethyl-2-methylmalonic acid diethyl ester and 2,2-dimethylmalonic acid diethyl ester. The former product was generated with quantitative deuterium incorporation from CDsCobjllljalamin. The proposed mechanism involves homolytic substitution on methylcob(III)alamin by the 2 -bis(ethoxycarbonyl)propyl radical, resulting in net methyl-radical abstraction, a process calculated to be highly exothermic (A7/ -201 kJmoK ). The stereochemical course of the reaction should result in net inversion at the methyl carbon, although this has not been demonstrated. The reaction may serve as a precedent for several biosynthetic methylations, such as the antibiotic thienamycin synthesis. ... 

In relation to the accepted mechanism, our main difference is the route by which the propyl radical is obtained. The calculations show that the direct H abstraction is an unfavorable process, because C-C bond scission requires less energy to proceed. However, once the methyl radicals are produced in this process, the reaction with propane is... 

From the point of view of the reaction mechanism, calculations agree with the experimental result that the CC bond in propane is easier to break than the CH bonds. However, it was also shown that methyl radicals produced this way can abstract hydrogens from other propane molecules forming the /i-propyl and /-propyl radicals. Although no attempt was performed in this paper to solve the full kinetic problem, a reduced mechanism is suggested, which proceeds through the formation of propene and ends up giving methane and butane, as observed experimentally. 

Reaction of butanal with all three reactive species leads primarily to the formation of the butanoyl radical by abstraction of the aldehydic H-atom. Papagni et al. (2000) noted an increase in the rate coefficient of OH with butanal, compared with that with propanal, which is compatible with the sensitization of the C—H bond to the carbonyl group proposed by Kwok and Atkinson (1995). Application of their structure-activity relations (SARs) gives 17% abstraction at this site with a channel yield of 78% for production of the acyl radical. Reaction of the acylperoxy radical with NO2 forms peroxybutanoyl nitrate, while reaction with NO forms CO2 and the -propyl radical, which then reacts with O2 to form the n-propylperoxy radical, whose main atmospheric fate is conversion to propanal. 

The peroxybutanoyl radical, formed following abstraction at the 1-position and reaction with O2, reacts with NO2 to form peroxybutanoyl nitrate (PBN). At 298 K, the lifetime for dissociation of PBN to regenerate peroxybutanoyl and NO2 is about 45 min. even for an NO2 mixing ratio of only 100 pptv, the ratio of [PBN] [peroxybutanoyl] is 80 at equilibrium and the timescale for establishment of the equilibrium is only 30 s. Reaction of PBN with OH to form propanal has a timescale of about 2.5 days for [OH] = 10 moleculecm , and so is not competitive. The peroxybutanoyl radical also reacts with NO, on a timescale of about 20 s for an NO mixing ratio of 100 pptv and forms the propyl radical and CO2. After reaction with O2 and then NO, this reaction channel leads to formation of propanal. 

In H abstraction, a hydrogen radical reacts with a molecule (primarily a paraffin) and produces a hydrogen molecule and a radical. In the same way, a methyl radical reacts to produce a radical and methane. Similar reactions with other radicals (ethyl and propyl) can also occur. In addition, some radicals like H, CH, etc, are added to olefins to form heavier radicals. 

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