Bonds redox reactions

Another essential component of free radical polymerization systems are initiators which should provide initiating free radicals via hemolytic cleavage of covalent bonds, redox reaction, photochemical or other stimuli. In addition, various... 

Yeom et al. demonstrated that the gold-catalyzed redox cyclization reaction of (Z)-isomer of o-alkynylaryl ketoximes (Z)-95 produced isoindole 96 (Scheme 27.34) [43]. The reaction proceeds through N—O bond redox reaction to form gold carbenoid intermediate 98 and subsequent cyclization and elimination of the gold catalyst, furnishing the isoindole 96. In contrast, reaction of the -isomer (E)-95 afforded isoqunoline oxide 100 [44],... 

The concept of oxidation number is used to simplify the electron bookkeeping in redox reactions. For a monatomic ion (e.g., Na+, S2 ), the oxidation number is, quite simply, the charge of the ion (+1, —2). In a molecule or polyatomic ion, the oxidation number of an element is a pseudo-charge obtained in a rather arbitrary way, assigning bonding electrons to the atom with the greater attraction for electrons. 

The oxidation states and reversible redox reactions of metalloporphyrins. J. H. Furhrhop, Struct. Bonding (Berlin), 1974,18,1-67 (221). 

Disiloxane, tetramesityl-, 3,206 Disproportionation iridium catalysts, 4,1159 Dissolution nuclear fuels, 6, 927 Distannene, 3,217 Distannoxane, 1,3-dichloro-, 3,207 Distibine, tetraphenyl-, 2,1008 Distibines, 2,1008 Disulfido ligands metal complexes, 2,531-540, 553 bonding, 2, 539 electron transfer, 2, 537 intramolecular redox reactions, 2,537 reactions, 2, 537... 

An irreversible reaction of the intermediate of a redox reaction will greatly facilitate redox catalysis by thermodynamic control. A good example is the reduction of the carbon halogen bond where the irreversible reaction is the cleavage of the carbon halogen bond associated, or concerted, with the first electron transfer -pEe... 

The sulfur-rich oxides S 0 and S 02 belong to the group of so-called lower oxides of sulfur named after the low oxidation state of the sulfur atom(s) compared to the best known oxide SO2 in which the sulfur is in the oxidation state +4. Sulfur monoxide SO is also a member of this class but is not subject of this review. The blue-green material of composition S2O3 described in the older literature has long been shown to be a mixture of salts with the cations S4 and Ss and polysulfate anions rather than a sulfur oxide [1,2]. Reliable reviews on the complex chemistry of the lower sulfur oxides have been published before [1, 3-6]. The present review deals with those sulfur oxides which contain at least one sulfur-sulfur bond and not more than two oxygen atoms. These species are important intermediates in a number of redox reactions of elemental sulfur and other sulfur compounds. 

Attempts to realize enzymatic reactions have been reported over the past four decades in the context of host-guest chemistry, presently a well-established research field. In the field of CPOs, much attention has been paid to identical research objectives. The host-guest chemistry based on CPOs holds a special position, because specific selectivity and reactivity will be achieved using the coordination-bond-forming reactions between the substrate and the incorporated metals in the porphyrins, as well as the redox reaction associated with the porphyrin s rr-electron system. 

These enzymes catalyze the addition of the elements of water to carbon-carbon double bonds (C=C), carbon-carbon triple bonds (C C), carbon-nitrogen double bonds (C=N), or carbon-nitrogen triple bonds (C N). These reactions are completely different from oxidoreductases since no redox reactions are involved. Illustrative examples include the following ... 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

Trigonal- and tetragonal-prismatic clusters are also characterized by redox reactions (15) and (16) changing the formal multiplicity of the M-M bonds in them (Sects 3.5 and 5.3). 

Initiation. Initiation in radical polymerisation consists of two steps the dissociation of the initiator to form two radical species, followed by addition of a single molecule to the initiating radical (Figure 18). Initiators include any organic compound with a labile group, such as an azo (-N = N-), disulfide (—S—S—) or peroxide (-0-0-) compound. The labile bond can be broken by various ways like heat, UV light, /-irradiation or by a redox reaction. 

Equilibrium considerations other than those of binding are those of oxidation/reduction potentials to which we drew attention in Section 1.14 considering the elements in the sea. Inside cells certain oxidation/reductions also equilibrate rapidly, especially those of transition metal ions with thiols and -S-S- bonds, while most non-metal oxidation/reduction changes between C/H/N/O compounds are slow and kinetically controlled (see Chapter 2). In the case of fast redox reactions oxidation/reduction potentials are fixed constants. 

Only transformations in the longest linear sequence (LLS) are considered. The term skeleton constructions refers to C-C and C-O bond formations (notwithstanding redox reactions) that directly introduce native structural features of the bryostatins without further modification. The term other functional group manipulations refers to steps that indirectly introduce native structural elements, the interconversion of functional groups (e.g., the introduction and removal of auxiliaries) and miscellaneous transformations that do not involve skeleton construction... 

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