Allyl radicals defined

Figure 4.2 Hiickel MOs for the allyl system. One pc orbital per atom defines the basis set. Combinations of these 3 AOs create the 3 MOs shown. The electron occupation illustrated corresponds to the allyl cation. One additional electron in

Typical experimental results are listed in Table V, Conversion of DAO, X, was defined based on the stoichiometry of the pyrolysis of DAO to allyl radicals and CO2 as x = (1/2) (moles of CO2 formed/moles of DAO fed). Product distribution was calculated on the basis of 100 moles of DAO converted. Fewer products were obtained than those in the reaction of diallyl in excess ethylene. Lower temperatures favored the formation of cyclopentene and 1-butene as compared to those of 1-pentene and butadiene, respectively ... 

As stated in section I, the termination mode of the particular monomer determines the number of functionalities per macromolecular chain. Most monomers undergo both unimolecular and bimolecular termination reactions. It is often observed that both respective monofunctional and bifunctional polymers are formed and well-defined functional polymers cannot be prepared. The use of allylmalonic acid diethylester in free-radical polymerization has been proposed to overcome the problems associated with the aforementioned functionality. In the presence of the allyl compound, the free-radical polymerization of monomers, regardless of their termination mode, proceeds entirely with the unimolecular termination mechanism, as shown in Scheme 9. Because allyl compounds lead to degradative chain transfer, the resulting allyl radical is quite stable due to the allyl resonance. Monofunctional polystyrene, polyvinylacetate, and poly(t-butyl methacrylate) were prepared by using this approach [33]. Subsequently, various macromonomers were derived from these polymers. 

In this case, the endothermicities of Reactions A-3 and A-4 are not equal since Reaction A-3 produces an allyl ladical. Therefore, one would expect Reaction A-3 to be somewhat faster than Reaction A—4. If Radicals I and II are present in equal concentrations, then the yield of nonene from the hydrogen-abstraction path is between one and two times the yield of octene. The nonene in excess of this is formed by the retro-ene reaction. This defines a range of importance for the molecular path and by difference the contribution of the hydrogen abstraction path. This procedure is illustrated for the dodecene cracking yields from column two of Table II. 

Within the past decade, diastereosolective radical reactions have become feasible and the factors contolling selectivity defined. Chiral auxiliaries for radical reactions have been recently developed in analogy to those developed for carban-ion chemistry in the 1970s and 1980s. The first example of stoichiometric use of a chiral ligand for enantioselective radical additions was recently reported by Porter and coworkers [59,60,61]. Reaction of the amide 14 with allyltrimethyl-silane at -78 °C, initiated by triethylborane, in the presence of 1 equiv. each of zinc triflate and the chiral bidentate ligand 15, provided the allylated product in a yield up to 88% and ee of 90%, Eq. (18). The presumed intermediate is the a-keto radical complexed to the chiral Lewis acid. 

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