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Carbon-centered free radicals

Cupric ion has a unique abitity to compete with oxygen for a carbon-centered free radical (compare reaction 2) ... [Pg.343]

In this chapter techniques of block copolymer preparation involving thermally labile azo compounds are reviewed. Upon heating, aliphatic azo compounds evolve nitrogen thus forming two carbon centered free radicals. [Pg.735]

Misra, H.P., Weglicki, W.B., Abdulla, R- and McCay, P.B. (1984). Identification of a carbon centered free radical during reperfusion injury in ischemic rat heart. Circulation II, 260 (abstract). [Pg.72]

Schreiber, J., Eling, T. E. and Mason, R. P. The oxidation of arachidonic acid by the cyclooxygenase activity of purified prostaglandin H synthase spin trapping of a carbon-centered free radical intermediate. Arch. Biochem. Biophys. 249 126-136,1986. [Pg.572]

FIGURE 5.15 Reductive dehalogenation of carbon tetrachloride results in a carbon-centered free radical that reacts rapidly with oxygen to form the toxic peroxy radical. [Pg.118]

FIGURE 8.23 One electron oxidation of a cyclopropyl amine leading to ring opening and the formation of a carbon-centered free radical and an iminium ion. [Pg.162]

Scheme 91 Generation of carbon-centered free radicals by vitamin Bn-photoelectrocatalysis. Scheme 91 Generation of carbon-centered free radicals by vitamin Bn-photoelectrocatalysis.
Scheme 92) [378]. A general mode of action for carbon-centered free radicals by Bi2-photoelectrocatalysis is depicted in... [Pg.551]

The previous chapter covered radical cation cyclization reactions that were a consequence of single-electron oxidation. In the following section, radical anion cyclization reactions arising from single-electron reduction will be discussed. In contrast to the well documented cyclization reactions via carbon-centered free radicals [3, 4], the use of radical anions has received limited attention. There are only a few examples in the literature of intramolecular reductive cyclization reactions via radical anions other than ketyl. Photochemi-cally, electrochemically or chemically generated ketyl radical anions tethered to a multiple bond at a suitable distance, have been recognized as a promising entry for the formation of carbon-carbon bonds. [Pg.101]

Artemisia derivatives that kill parasites via carbon-centered free radicals... [Pg.586]

The reaction of carbon-centered free radicals with O2 is one of the distinguishing features of these intermediates (equations 1, 34, 35). The formation of peroxyl radicals 43 in hydrocarbon oxidation (equation 68) has been of continued interest, " including the important role in biological processes. Peroxyl radicals may also be formed by H atom abstraction from hydroperoxides. [Pg.30]

Desaturation of alkyl groups. This novel reaction, which converts a saturated alkyl compound into a substituted alkene and is catalyzed by cytochromes P-450, has been described for the antiepileptic drug, valproic acid (VPA) (2-n-propyl-4-pentanoic acid) (Fig. 4.29). The mechanism proposed involves formation of a carbon-centered free radical, which may form either a hydroxy la ted product (alcohol) or dehydrogenate to the unsaturated compound. The cytochrome P-450-mediated metabolism yields 4-ene-VPA (2-n-propyl-4pentenoic acid), which is oxidized by the mitochondrial p-oxidation enzymes to 2,4-diene-VPA (2-n-propyl-2, 4-pentadienoic acid). This metabolite or its Co A ester irreversibly inhibits enzymes of the p-oxidation system, destroys cytochrome P-450, and may be involved in the hepatotoxicity of the drug. Further metabolism may occur to give 3-keto-4-ene-VPA (2-n-propyl-3-oxo-4-pentenoic acid), which inhibits the enzyme 3-ketoacyl-CoA thiolase, the terminal enzyme of the fatty acid oxidation system. [Pg.92]

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. [Pg.147]

Addition to n bonds is a second very common reaction of free radicals. Interaction of die free radical widi die 7r -electron pah causes one of die n electrons to pair up widi die unpaired electron of the free radical to produce a new bond to one of die r-bonded atoms. The remaining n electron is now unpaired and dius forms a new free-radical species. The process is often very favorable since the new a bond (70-90 kcal/mol) formed in die addition process is normally much stronger than die jt bond (60 kcal/mol) which is broken in the reaction. In the above example a new carbon-carbon a bond is formed by free-radical addition to produce a new carbon-centered free radical however, a wide variety of other free-radical species add readily to olefins. [Pg.75]

Another way to form a bond between two carbons is for each carbon atom to supply one electron. In this case interaction between two carbons which each has a single, unshared electron would result in formation of a carbon-carbon bond. Species with unshared electrons are called free radicals, and dius formation of carbon-carbon bonds by this strategy requires carbon-centered free radicals as reactants. [Pg.273]

The reactivity of carbon-centered free radicals results from dieir drive to achieve an octet electronic configuration, which they do by two principal reaction processes. The first is atom transfer. This process is one in which an atom with one electron is transferred from a closed-shell molecule (fully paired, valence octets) to the free radical. [Pg.273]

This process is quite common for carbon-centered free radicals because die carbon-carbon a bond which is formed is stronger by about 30 kcal dian die n bond which is broken. Other radical species, however, are well known to undergo olefin additions as well. The addition of bromine to olefins is die key step in the anti-Markovnikov addition of HBr to olefins. [Pg.274]

Besides new insight into the reactivity of free radicals, methods for die production of carbon-centered free radicals have also seen major improvements in die last several years. One very common new mediod is to use tin-based reagents as radical chain carriers. Trialkyltin radicals readily abstract bromine or iodine from carbon to produce a carbon-centered free radical. Placement of a bromide or iodide substituent on a substrate dius permits formation of a carbon-centered free radical at diat position using tin-based mediodology. This process was initially developed for die reduction of alkyl halides, and it remains an excellent synthetic method for diat purpose. The complete chain mechanism for die reduction is shown. [Pg.280]

With good methods available for producing carbon-centered free radicals, the cyclization process can be examined in greater detail. Cyclization involves the intramolecular addition of a free-radical to a double bond. Of course, this requires that the two reacting parts of the molecule, the free-radical center and the n bond, come within bonding distance of one another. [Pg.283]

The mechanism of action for such peroxidic compounds involves a reductive activation by iron in haem, released as a result of hemoglobin digestion by Plasmodium. This irreversible redox reaction affords carbon-centered free radicals causing the alkylation of haem and of proteins. One such protein (the sarcoplasmic-endoplasmic reticulum ATPase PfATP6) appears to be critical for parasite survival, and there is no indication for resistance by the parasite. However, treatment is expensive and recrudescence of malaria occurs often. Moreover, it was found that at high doses such compounds are neurotoxic. [Pg.249]

First, one had to check that the mechanism of action was correct. The product of co-ozonlysis of O-methyl-2-adamantanone oxime with 1,4-cyclohexanedione afforded on treatment with ferrous acetate a secondary carbon-centered free radical that was trapped with the usual spin trap, 2,2,6,6-tetramethylpiperidine-Ar-oxide (TEMPO), and involved a /3-scission of the adamantane fragment, thus proving that the attack of the Fe(ll) species occurred on the less-hindered peroxide bond oxygen atom (Scheme 85) <2004NAT900, 2005JOC513>. [Pg.249]

Tortolani, A.J., Powell, S.R., Misik, V., Weglicki, W.B., Pogo, G.J., and Kramer, J.H. 1993. Detection of alkoxyl and carbon-centered free radicals in coronary sinus blood from patients undergoing elective cardioplegia. Free Radical Biol. Med. 14 421 126. [Pg.154]

Recent reports show unexpected information on the role of free radicals in the health effects of nanotubes currently employed in many industries.31 Unlike asbestos and most toxic particles, nanotubes do not release but blunt free radicals, which are considered one of the features imparting toxicity to particulates. Multi-wall carbon nanotubes (MWCN) in aqueous suspension do not generate oxygen or carbon centered free radicals detectable with the spintrapping technique. Conversely, when in contact with an external source of hydroxyl (HO) or superoxide radicals (CL h MWCN exhibit a remarkable radical scavenging capacity (Figure 3). It is therefore possible that the inflammatory reaction reported in vivo should be ascribed to MWCN features other than particle derived free radical generation. [Pg.249]

Among protein oxidation products, formation of protein peroxides should be mentioned. Protein peroxidation occurs as a reaction secondary to free-radical attack on amino acid side groups, effecting a carbon-centered free radical of amino acid formation. Such a radical reacts with the oxygen molecule and produces a hydroperoxide radical ... [Pg.193]


See other pages where Carbon-centered free radicals is mentioned: [Pg.495]    [Pg.1104]    [Pg.253]    [Pg.805]    [Pg.816]    [Pg.816]    [Pg.161]    [Pg.56]    [Pg.806]    [Pg.817]    [Pg.817]    [Pg.147]    [Pg.148]    [Pg.933]    [Pg.148]    [Pg.1104]    [Pg.43]    [Pg.16]    [Pg.273]    [Pg.318]    [Pg.68]    [Pg.27]    [Pg.27]    [Pg.193]    [Pg.1]   
See also in sourсe #XX -- [ Pg.273 , Pg.274 ]

See also in sourсe #XX -- [ Pg.228 ]




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Carbon centers

Carbon free

Carbon radicals

Carbon-Centered Free Radicals and Radical Cations, Edited by Malcolm D. E. Forbes

Carbon-centered

Carbon-centered free radicals properties

Carbonate radical

Centered Radicals

Free Radicals, carbon

Free radicals carbonate

Radical centers

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