Radical ethyl

Hase W L and Buckowski D G 1982 Dynamics of ethyl radical decomposition. II. Applicability of classical mechanics to large-molecule unimolecular reaction dynamics J. Comp. Chem. 3 335-43... 

Figure 5.23 reprinted with permission from Doubleday C, J Mclver, M Page and T Zielinski. Temperature Dependence of the Trcmsition-State Structure for the Disproportionation of 1 lydrogen Atom with Ethyl Radical. The Journal of the American Chemical Society 107 5800-5801. c,1985 American Chemical Society. 

As the table indicates C—H bond dissociation energies m alkanes are approxi mately 375 to 435 kJ/mol (90-105 kcal/mol) Homolysis of the H—CH3 bond m methane gives methyl radical and requires 435 kJ/mol (104 kcal/mol) The dissociation energy of the H—CH2CH3 bond m ethane which gives a primary radical is somewhat less (410 kJ/mol or 98 kcal/mol) and is consistent with the notion that ethyl radical (primary) is more stable than methyl... 

Cleavage of the carbon-carbon bond in ethane yields two methyl radicals whereas propane yields an ethyl radical and one methyl radical Ethyl radical is more stable than methyl and so less energy is required to break the carbon-carbon bond in propane than in ethane The measured carbon-carbon bond dissociation energy in ethane is 368 kJ/mol (88 kcal/mol) and that in propane is 355 kJ/mol (85 kcal/mol)... 

The characteristic times for waste destmction to an efficiency of 99.99%, for water in a nitrogen atmosphere, where the residue is a typical hydrocarbon breaking into two large fragments, eg, / -butane decomposing into two ethyl radicals would be droplet heatup, 0.073 s droplet evaporation,... 

Because high temperatures are required to decompose diaLkyl peroxides at useful rates, P-scission of the resulting alkoxy radicals is more rapid and more extensive than for most other peroxide types. When methyl radicals are produced from alkoxy radicals, the diaLkyl peroxide precursors are very good initiators for cross-linking, grafting, and degradation reactions. When higher alkyl radicals such as ethyl radicals are produced, the diaLkyl peroxides are useful in vinyl monomer polymerizations. 

The EPR spectrum of the ethyl radical presented in Fig. 12.2b is readily interpreted, and the results are relevant to the distribution of unpaired electron density in the molecule. The 12-line spectrum is a triplet of quartets resulting from unequal coupling of the electron spin to the a and P protons. The two coupling constants are = 22.38 G and Op — 26.87 G and imply extensive delocalization of spin density through the a bonds Note that EPR spectra, unlike NMR and IR spectra, are displayed as the derivative of absorption rather than as absorption. 

Fig. 12.2. EPR spectra of small organic free radicals, (a) Spectrum of the benzene radical anion. [From J. R. Bolton, Mol. Phys. 6 219 (1963). Reproduced by permission of Taylor and Francis, Ltd.] (b) Spectrum of the ethyl radical. [From R. W. Fessenden and R. H. Schuler, J. Chem. Phys. 33 935 (1960) J. Chem. Phys. 39 2147 (1963). Reproduced by permission of the American Institute of Physics.]...

If other possible termination steps are considered, then it can be inferred that recombination or disproportionation of ethyl radicals, c,H5 is more likely than recombination of C and. Step 5... 

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular- ion peak in their mass spectra. Aldehydes also exhibit an M— 1 peak. A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acyliurn ions) by cleavage of an alkyl group from the carbonyl. The most intense peak in the mass spectrum of diethyl ketone, for exanple, is m/z 57, conesponding to loss of ethyl radical from the molecular- ion. 

Another interesting example is found in the morpholine enamine of 2- -propylcyclohexanone (138), which consists of a 2 3 mixture of tri- and tetrasubstituted isomers. The radical ion from the tetrasubstituted isomer loses an ethyl radical, giving the base peak at m/e 180. 

Free radical initiators play an important role in many chemical reactions (see also Chapter 17, Problem 5). For example, combustion of gasoline is assisted by compounds such as tetraethyl lead, heating of which results in bond breaking and generation of ethyl radical. 

In the reaction of 2,3,3-triethyloxazirane (25), three radicals are involved 26, 27, and 28. Radical 26 (Fig. 1) corresponds to the chain reaction propagating radical of the previously mentioned decomposition [Eqs. (20) and (21)]. From 26 hy fragmentation an ethyl radical (27) is formed together with the acid amide. Finally, by radical attack on the oxazirane, 29 can be formed which rearranges to the... 

Into this compound, an ethyl radical is introduced at the same C-atom to which the cyclo-heptenyl radical is connected. This Is done, for example. In the following way ... 

Large volumes of gas are generated, primarily ethane and ethylene, from the disproportionation of the ethyl radicals produced in the reaction of ethylmagnesium bromide with ferric chloride. The reaction should be carried out in an efficient hood, or else a tube should be run from the top of the reflux condenser to a hood. 

Table 1.7 Values of for the Cross-Reaction between Fluoromethyl and Ethyl Radicals (25 °C) 172174...

Thus, even if /-amyloxy radicals (101) show similar specificity for addition 1 5-abstraction to /-butoxy radicals, abstraction will be of lesser importance.42"42 The reason is that most /-amyloxy radicals do not react directly with monomer. They undergo [3-scission and initiation is mainly by ethyl radicals. Ethyl radicals are much more selective and give addition rather than abstraction. This behavior has led to /-amyl peroxides and peroxyesters being promoted as superior to the corresponding /-butyl derivatives as polymerization initiators.423... 

ESI mass spectrometry ive mass spectrometry ESR spectroscopy set EPR spectroscopy ethyl acetate, chain transfer to 295 ethyl acrylate (EA) polymerizalion, transfer constants, to macromonomers 307 ethyl methacrylate (EMA) polymerization combination v.v disproportionation 255, 262 kinetic parameters 219 tacticity, solvent effects 428 thermodynamics 215 ethyl radicals... 

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