Addition bonds, radical

The peioxy free radicals can abstract hydrogens from other activated methylene groups between double bonds to form additional hydroperoxides and generate additional free radicals like (1). Thus a chain reaction is estabhshed resulting in autoxidation. The free radicals participate in these reactions, and also react with each other resulting in cross-linking by combination. 

Addition of small amounts of (CH3)2S (5 x 10 5 — 5 x 10"4m) to deoxygenated solutions of 3m HC104 and 0.5m DMSO leads to replacement of the 285 nm absorption by 465 nm absorption which is known to belong to the complexed three-electron-bonded radical cation of the disulfide47. 

In certain cases, Michael reactions can take place under acidic conditions. Michael-type addition of radicals to conjugated carbonyl compounds is also known.Radical addition can be catalyzed by Yb(OTf)3, but radicals add under standard conditions as well, even intramolecularly. Electrochemical-initiated Michael additions are known, and aryl halides add in the presence of NiBr2. Michael reactions are sometimes applied to substrates of the type C=C—Z, where the co-products are conjugated systems of the type C=C—Indeed, because of the greater susceptibility of triple bonds to nucleophilic attack, it is even possible for nonactivated alkynes (e.g., acetylene), to be substrates in this... 

Perhaps the most characteristic property of the carbon-carbon double bond is its ability readily to undergo addition reactions with a wide range of reagent types. It will be useful to consider addition reactions in terms of several categories (a) electrophilic additions (b) nucleophilic additions (c) radical additions (d) carbene additions (e) Diels-Alder cycloadditions and (f) 1,3-dipolar additions. 

Next, we examined the reduction of cation pools in the presence of radical acceptors. The radical that is formed by one-electron reduction of the cation is expected to add to a carbon-carbon double bond. The electrochemical reduction of 2 in the presence of methyl acrylate gave the expected addition product 16 (Scheme 9). A mechanism involving addition of radical 14 to the acrylate to generate radical 17 followed by subsequent reduction of anion 18, which is protonated to give 16 has been suggested. 

Addition of radicals to carbon-carbon or carbon-heteroatom multiple bonds followed by the trapping of resulting radicals with a hydrogen atom source... 

Because of the weight of 43, the system 41/43 undergoes an easier rotation about its formally Ge = C double bond than about its formally C-C single bond. The diradical character of 41 should favor any addition with radical intermediates and polymerization reactions.45... 

A review on the nitration of aromatics (using a range of species including N02 and NO3) has appeared. Evidence for electron-transfer mechanisms via radical cations has been reviewed. In addition, another review comparing the reactivity of a range of radicals and radical cations has appeared. While radicals prefer to add to the carbon of CN triple bonds, radical cations were found to prefer addition at the N atom. Ab initio calculations were performed to rationalize this behaviour. 

A general type of chemical reaction between two compounds, A and B, such that there is a net reduction in bond multiplicity (e.g., addition of a compound across a carbon-carbon double bond such that the product has lost this 77-bond). An example is the hydration of a double bond, such as that observed in the conversion of fumarate to malate by fumarase. Addition reactions can also occur with strained ring structures that, in some respects, resemble double bonds (e.g., cyclopropyl derivatives or certain epoxides). A special case of a hydro-alkenyl addition is the conversion of 2,3-oxidosqualene to dammara-dienol or in the conversion of squalene to lanosterol. Reactions in which new moieties are linked to adjacent atoms (as is the case in the hydration of fumarate) are often referred to as 1,2-addition reactions. If the atoms that contain newly linked moieties are not adjacent (as is often the case with conjugated reactants), then the reaction is often referred to as a l,n-addition reaction in which n is the numbered atom distant from 1 (e.g., 1,4-addition reaction). In general, addition reactions can take place via electrophilic addition, nucleophilic addition, free-radical addition, or via simultaneous or pericycUc addition. 

In intramolecular additions of radicals containing a 5,6 double bond,50 both five- and six-membered rings can be formed, but in most cases91 the five-membered rings are greatly preferred kinetically, even (as in the case shown) where five-membered ring closure means... 

B. Giese, Formation of carbon-carbon bonds by addition of radicals to alkenes, Angew. Chern. Int. Ed Engl. 22 153 (1983). 

C-Alkylations have been performed with both support-bound carbon nucleophiles and support-bound carbon electrophiles. Benzyl, allyl, and aryl halides or triflates have generally been used as the carbon electrophiles. Suitable carbon nucleophiles are boranes, organozinc and organomagnesium compounds. C-Alkylations have also been accomplished by the addition of radicals to alkenes. Polystyrene can also be alkylated under harsh conditions, e.g. by Friedel-Crafts alkylation [11-16] in the presence of strong acids. This type of reaction is incompatible with most linkers and is generally only suitable for the preparation of functionalized supports. Few examples have been reported of the preparation of alkanes by C-C bond formation on solid phase, and general methodologies for such preparations are still scarce. 

The electron-nch carbon-carbon double bond reacts with reagents that are deficient in electrons, e.g., with electrophilic reagents in electrophilic addition, free radicals in free-radical addition, and under acidic conditions with another butylene (cation) in dimerization. 

All evidence on addition of radicals to ethenylbenzene indicates that the process by which X- adds to the CH2 end of the double bond is greatly favored over addition at the CH end. This direction of addition is in accord with the... 

Addition of radicals to carbon-carbon double bonds, ordinarily by a chain process, may lead to the formation of either small molecules or polymers, depending upon the efficiency of chain transfer. 

Redox and homolytic substitution reactions almost never directly form C—C, C—N and C—O bonds. Such bonds are generated in radical addition reactions (Scheme 14). Intermolecular addition reactions are presented in this chapter. Cyclization reactions have important similarities with, and differences from, bimolecular additions, and they are presented in Chapter 4.2 of this volume. Falling under the umbrella of addition reactions are radical eliminations (the reverse of addition) and radical migrations (which are usually, but not always, comprised of an addition and an elimination). 

Other research in tire area of addition reactions onto unsaturated carbon-carbon bonds has included measurement of the rate coefficients for tire addition of NO3 to chloro- and trichloro-ethene,147 relative rate measurement for N03 addition to isoprene,148 TF-/(SR-measured muonium addition to vinyl aromatics12 and EPR studied addition of radical (65) to alkenes.150 In this latter study a linear dependence of the rate constant of addition with tire donor/acceptor properties of the alkene partner was highlighted. 

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