Radicals examples

Amines. Amines are preferably named by adding the suffix -amine (and any multiplying affix) to the name of the parent radical. Examples are... 

When another group having higher priority for citation as principal group is also present, the ketonic oxygen may be expressed by the prefix 0x0-, or one can use the name of the carbonyl-containing radical, as, for example, acyl radicals and oxo-substituted radicals. Examples are... 

There are many varieties of free radical initiators. Chemical initiators decompose to create radicals examples include organic peroxides, azo compounds, or even oxygen. More rarely we initiate polymerization via a physical condition, such as heat or high energy radiation, to create free radicals directly from the monomers. 

As for any chain reaction, radical-addition polymerization consists of three main types of steps initiation, propagation, and termination. Initiation may be achieved by various methods from the monomer thermally or photochemically, or by use of a free-radical initiator, a relatively unstable compound, such as a peroxide, that decomposes thermally to give free radicals (Example 7-4 below). The rate of initiation (rinit) can be determined experimentally by labeling the initiator radioactively or by use of a scavenger to react with the radicals produced by the initiator the rate is then the rate of consumption of the initiator. Propagation differs from previous consideration of linear chains in that there is no recycling of a chain carrier polymers may grow by addition of monomer units in successive steps. Like initiation, termination may occur in various ways combination of polymer radicals, disproportionation of polymer radicals, or radical transfer from polymer to monomer. 

The intermolecular coupling of phenols is used extensively in what are believed to be biomimetic alkaloid syntheses. Aqueous solutions of iron(lll) salts are most frequently used as the oxidising agent and the dimerization process must involve phenoxy radicals. Examples are the dimerization of orcinol 21 [114] and the formation of bis-benzyltetrahydroisoquinolines 22 [115],... 

Fig. 15 Unimolecular pathways available to heteroaromatic peroxy radicals example shown for 2-pyridinylperoxy radical. Adapted from Reference 198.

Vinyiidene Resins (Poly vinyiidene Resins), These are resins in which the unit structure in the polymer molecule is (-H2C.CX2—). Here the X usually stands for F, Cl or CN radical. Examples are Saran , Viton A and "Gene-1132A ... 

There also exist systems in which a coloured species is decolourized in an imagewise manner. These positive working processes rely on the imagewise destruction of highly coloured, stable free radicals, examples of which include the verdazyls (158), the bipyridyls (159) and the nitroxide radical (160) (B-69MI11402). 

The C—H bond is normally not very polar. As a result, the <7Ch and ch orbitals are widely separated and more or less symmetrically disposed relative to a. A sluggish reaction is expected with carbon free radicals, but a rapid reaction may be anticipated with both electrophilic and nucleophilic free radicals. Examples of both kinds of reactions are ubiquitous in organic chemistry. An ab initio investigation of the former, involving oxygen-centered free radicals, has been carried out [237], The reactivity spectrum may be modified by substitution on the carbon bearing the hydrogen atom. As we have seen in Chapter 7, all three kinds of substituents stabilize the carbon-centered free-radical intermediate. 

This example is important because carbon bond fragmentations occur at the first stages of the cation radical evolutions in cases of tert-butylated analogues of NADH (Fukuzumi et al. 1993). Scheme 6-48 describes this double-way fragmentation of the 9-tert-butyl-iV-methylacridan cation radical. Examples of the cation radical deprotonation-fragmentation of alcohols also deserve consideration. Hammerum and Audier described the reactions in 1988 ... 

As already demonstrated, stannane chemistry often involves the intermediacy of free radicals. There are some notable examples, however, of non-radical transformations involving trialkyltin hydrides. This (much smaller) subset of reactions is dominated by transition metal catalysed hydrostannylation chemistry551,808-860, chemistry that rivals the free-radical examples provided above. In addition, there are a few examples of ionic reduction chemistry involving these reagents861,862. 

A number of other transition metal ions can also participate in Fenton-type cycles to produce hydroxyl radical. Examples include Cu+, V02+, Ti3+, Cr2+, and Co2+ [4], although other reducing metals are also active in the formation of hydroxyl radical from peroxide. 

Radicals can also be generated by the action of ultraviolet or visible light on certain compounds. As described in Chapter 15, when a compound is excited by absorbing a photon of light, an electron is promoted to an unoccupied orbital. Because this orbital is usually antibonding in character, some bond in the excited molecule is weakened and may cleave in a homolytic fashion. For this reason, many photochemical reactions involve radicals. Examples of photochemically induced homolytic bond cleavages are... 

Cationic rings are reduced with the uptake of one electron (e.g., electrochemically) to give neutral radicals. Examples of radicals which have been detected by ESR are 373 and 374. Such radicals, e.g., those 376 from benzothiazolium ions, can dimerize (to 377) or undergo further reduction (to 378) in practice, a mixture of the dihydro derivative 378 and the dimer 377 is obtained. Benzofurazan is reduced polarographically in a six-electron reaction to o-phenylenediamine. 

Organic peroxides (ROOR) and hydroperoxides (ROOM). These compounds are thermally unstable and decompose thermally by cleavage of the oxygen bond to yield RO and HO radicals. Examples of this type of initiators include... 

A more common process seems to be the formal abstraction of an O radical by another radical. Examples are known where the O donor is also radical as in... 

Antioxidants which prevent oxidation by reaction with alkyl radicals. The additives react quickly with alkyl radicals. Examples of such additives are hynones, iminehynones, methylhynones, stable nitrogen oxide radicals, and molecular iodine. Alkyl radicals react quickly with oxy-... 

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