Homolytic bond fission reactions

Homolytic Bond Fission Reactions. The homolytic fission of a chemical bond... 

Above 383 K, the favored decomposition pathway produces NO2 in a homolytic bond fission reaction ... 

As described above, models for l pin-derived biofuels typically utilize derivatives of PPEs (PhCH2CH20Ph) or similar molecules as surrogates for the more compHcated rmits in hgnin (Figure 7). The mechanistic studies in this area focus on the compHcated pyrolytic decomposition pathways for the surrogate ethers. A strong temperature dependence to the reaction charmels is observed with a competition between homolytic bond fission reactions and a concerted retro-ene reaction. 5-Scissions following H atom abstractions, H atom transfer reactions, and the influence of... 

In effect we postulate that the olefin ion is formed by a 1-3 hydride ion shift accompanied by a beta homolytic bond fission. The fact that olefin ions are formed only at branch points (except methyl branch points) could be explained on an energetic basis if it were not for the contrary fact that the over-all energetics are highly unfavorable. Thus in Reaction 20 we see that a disubstituted olefin ion is formed, and this will be true for any branch other than a methyl branch. Thus ... 

A number of reactions of compounds containing the nitro group are postulated to occur by an isomerization to give the nitrite form —NO2 - —ONO, which is often followed by O—N homolytic bond fission releasing nitric oxide. The reaction has been extensively examined theoretically, for example in nitromethane. Calculations have led to values for the barrier height and characteristics of the transition state have been established (see, for example, Reference 87). The question of the nitro-nitrite rearrangement within the... 

With methane, transition-metal ions undergo oxidative addition to give the methyl hydride. The subsequent chemistry depends upon the initial energy of the ion. At low energies H2 is eliminated through a 4-centre reaction (equation 18a) while at higher energies homolytic bond fission occurs and H or, more commonly, CH3 is lost (equation 18b). 

To avoid synthetic problems, we prepared aldehyde 47, a substrate in which isomerization of the C-C double bond to the endocyclic position is less likely due to the extended conjugation of the alkene moiety. Compound 47 was obtained as a pure substance and also presents a substitution pattern that, according to the above postulates, should favor the ODPM rearrangement. However, irradiation of 47, using m-methoxyacetophenone as sensitizer, led to formation of the diene 48 (38%), as a result of photodecar-bonylation (Scheme 9). No ODPM product was formed in this process.Irradiation of the corresponding methyl ketone 49, under the same conditions as used for 47, afforded the product of 1,3-acyl migration 50 in 24% yield (Scheme 9). Again, no ODPM product was formed in this instance. The formation of 48 and 50 is reminiscent of Norrish Type 1 processes. However, in these cases, homolytic bond fission does not occur in the carbonyl nit excited state, as is the case in normal Norrish Type 1 reactions. ... 

As far as we are aware, these observations show for the first time that the well-known Norrish Type 1 reactions of P,y-unsaturated carbonyl compounds can take place by excitation of the alkene moiety rather than the carbonyl group. The reason for this unusual reactivity may be that the Tj (itit ) excited states of 47 and 49 have sufficient energy to promote the homolytic bond fission between the carbonyl and the a-carbon due to the stabihty of the resulting pentadienyl radical 51. As a consequence, the photodecar-bonylation path competes favorably with the ODPM rearrangement. 

JOC1537). The mechanisms of these transformations may involve homolytic or heterolytic C —S bond fission. A sulfur-walk mechanism has been proposed to account for isomerization or automerization of Dewar thiophenes and their 5-oxides e.g. 31 in Scheme 17) (76JA4325). Calculations show that a symmetrical pyramidal intermediate with the sulfur atom centered over the plane of the four carbon atoms is unlikely <79JOU140l). Reactions which may be mechanistically similar to that shown in Scheme 18 are the thermal isomerization of thiirane (32 Scheme 19) (70CB949) and the rearrangement of (6) to a benzothio-phene (80JOC4366). 

In any reaction in chemistry, bonds in the reactants are broken and bonds in the products are made. The process of breaking bonds is known as bond fission and there are two types of bond fission homolytic fission and heterolytic fission. 

Thermal decomposition in three different ways, i.e. homolytic, polar and radical induced decomposition, as well as intermolecular reaction of sulfonyl peroxides are the main reactions displayed by sulfonyl peroxides. When bis(arylsulfonyl) peroxides are allowed to decompose at 25-40 °C in chloroform, homolytic 0—0 bond fission followed by hydrogen abstraction from the solvent results in the formation of the corresponding arylsnlfonic acids. Mixed acyl sulfonyl peroxides undergo complicated thermal decomposition in solution, and have been used commercially as polymerization initiators, since they provide a source of free radicals at a relatively low temperature . 

The excitation leads to homolytic M-L bond fission. Such a reactivity is not expected ol d-d band and if redox reaction does occur under such excitation it is likely to hide a low lying reactive CT type band under its envelop. 

A second process that has been invoked is heterolytic fission of H2.49 Examples are shown in equations (15) and (16). Although the overall process certainly involves heterolysis, some or all of these reactions may well go via initial oxidative addition followed by fast deprotonation or reductive elimination (equation 17). A third variant closely related to heterolytic fission is the addition of hydrogen across a metal-ligand or metal-metal bond. Examples are shown in equations (18) and (19). Here too, homolytic addition via equation (1) followed by fast reductive elimination may be taking place in some cases. In d° systems, the homolytic fission reaction of equation (1) is unlikely as the metal is already at its maximum valency, so examples of heterolytic fission and addition to... 

The corrinoid-mediated reduction of polyhaloethenes has been the subject of a recent study, which reports reaction via homolytic C-halogen bond fission. The elimination of a further halogen radical affords haloalkynes, which lead to acetylene itself.56 The electron transfer-induced reductive cleavage of alkyl phenyl ethers with lithium naphthalenide has been re-examined in a study which showed that it is possible to reverse regioselectivity of the cleavage (i.e. ArOR to ArH or ArOH) by introduction of a positive charge adjacent to the alkyl ether bond.57 A radical intermediate has been detected by ESR spectroscopy in the reduction of imines to amines with formic acid58 which infers reacts takes place via Lukasiewicz s mechanism.59... 

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