Radical common

From here, the saturation factor requires further discussion. Equation (9) is correct for radicals with a single ESR transition however, the picture becomes more complicated for radicals with more than one transition due to hyperfine splitting. The nitroxide radicals commonly used for ESR and DNP fall into this category,47 48 as the impaired electron in these molecules partially resides on a nitrogen nucleus with spin 1 (14N) or spin 1/2 (15N) giving three or two hyperfine lines, respectively. For the more common 14N nitroxide radicals, at low concentrations in aqueous solutions the right side of Equation (9) is multiplied by a factor of 1 /3, as only one hyperfine line can be saturated at a time.49 However, two processes can serve to mix the hyperfine lines and increase the saturation factor in the limit of infinite power (smax) of nitroxide radicals well beyond smax = 1/3. 

Hydroxyl group. The —OH radical, common to alcohols and water and responsible for their similarities of behavior. 

The one-electron oxidant reactive species (F° = 2.5 V) is another radical commonly employed by radiation chemists to mimic the direct effect of radiolysis in dilute aqueous solutions. 

The peroxide radical can go to a product by abstraction and generate for example an acid and another radical. Commonly, acetic acid and also formic acid are formed in considerable amount during oxidative pyrolysis. The previous mechanism can probably explain the formation of these small molecules. The oxygen (singlet oxygen) may also react with the double bond forming a dioxetane intermediate ... 

The energy required to break homolytically the R-H bond into R- and H radicals is related to the stability of the R- radical. Common C-H bond dissociation energies in kcal/mol (kJ/mol) are given in Table 11.1. 

During polymerization, parameters such as temperature, flow rate, and agitation speed must be controlled carefully to get the right conversion. Polymerization is normally allowed to proceed to about 60% conversion in cold polymerization and 70% in hot polymerization before it is stopped with a terminal agent that reacts rapidly with the free radicals. Common terminal agents include sodium dimethyldithiocarbamate and diethyl hydroxylamine. 

Simatos et al. (1981) measured the mobility of a spin-label probe, TEMPO, a stable free radical commonly used for electron paramagnetic resonance (EPR) spectroscopy. She found that the probe showed no mobility below a critical that correlated to Wq. A critical a also existed at which the probe demonstrated a partitioning into a dissolved and a solid-like state. This critical a could represent the moisture content correlating to Tg, though this concept had not been introduced in foods at that time. The partitioning of a... 

The oxidation of ascorbic acid in certain reactions has given evidence of an intermediate with the properties of a free radical which could be formed by one-electron oxidation. Thus, the rate-limiting step of ascorbic acid oxidation by Fe + and H2O2 was this one-electron oxidation (G12). Such a radical has now been identified in hydrogen peroxide-ascorbic acid solutions at pH 4.8 by electron paramagnetic resonance spectroscopy. The free radical, commonly referred to as monodehydroascorbic acid, decayed in about 15 minutes at this acid pH. It was also formed during the enzymatic oxidation of ascorbic acid by peroxidase (Yl). The existence of the monodehydroascorbic acid radical makes possible very... 

The formation of an open-shell radical commonly results in a low-lying electronic hole that greatly enhances acceptor character, or a weakly bound surplus electron with correspondingly enhanced donor character. As a residt, low-order perturbative approximations such as 7.5-7.8 must be replaced by multireference NRT to describe the donor-acceptor interactions. 

Tavema Porro ML, Greenberg MM. Double-strand breaks from a radical commonly produced by DNA-damaging agents. Chem Res Toxicol. 2015 28 810-816. 

After the initial nonstationary period, typical alkene polymerizations in the presence of aUcoxyamines proceed according to the first order kinetics with the molecular weights increasing with conversion. The dispersity of the products and the contribution of the nonstationary periods depend upon the temperature, the particular initiating system and on the nature of the monomers. Styrene polymerizations can be carried out in the presence of stable nitroxyl radicals, such as the 2,2,6,6-tetramethylpiperydinyl-l-oxy radical, commonly referred to as TEMPO [264] or ditertiary butyl nitroxide, referred to as DTB N. 

Prior to the formation of any final products, free radicals commonly undergo various transformations and reactions, both with intact moieties and other free radicals. The mechanisms of these processes have been proposed in the literature [80,83]. 

The additives for improving the cetane number, called pro-cetane, are particularly unstable oxidants, the decomposition of which generates free radicals and favors auto-ignition. Two families of organic compounds have been tested the peroxides and the nitrates. The latter are practically the only ones being used, because of a better compromise between cost-effectiveness and ease of utilization. The most common are the alkyl nitrates, more specifically the 2-ethyl-hexyl nitrate. Figure 5.12 gives an example of the... 

In contrast to the ionization of C q after vibrational excitation, typical multiphoton ionization proceeds via the excitation of higher electronic levels. In principle, multiphoton ionization can either be used to generate ions and to study their reactions, or as a sensitive detection technique for atoms, molecules, and radicals in reaction kinetics. The second application is more common. In most cases of excitation with visible or UV laser radiation, a few photons are enough to reach or exceed the ionization limit. A particularly important teclmique is resonantly enlianced multiphoton ionization (REMPI), which exploits the resonance of monocluomatic laser radiation with one or several intennediate levels (in one-photon or in multiphoton processes). The mechanisms are distinguished according to the number of photons leading to the resonant intennediate levels and to tire final level, as illustrated in figure B2.5.16. Several lasers of different frequencies may be combined. 

Ab-initio calculations are particularly usefiil for the prediction of chemical shifts of unusual species". In this context unusual species" means chemical entities that are not frequently found in the available large databases of chemical shifts, e.g., charged intermediates of reactions, radicals, and structures containing elements other than H, C, O, N, S, P, halogens, and a few common metals. 

Benzoyl peroxide has been the most common source of phenyl radicals. But in reaction with thiazoles the benzoyloxy radical abstracts a hydrogen atom from the thiazole nucleus or from a methyl group in the case of methylthiazoles, giving by-products such as dithiazolyls or 2.2 -dithiazolylethane (183). The results obtained with benzoyl peroxide are summarized in Tables III-23, III-24. and III-25. 

The thiazolyl radicals are, in comparison to the phenyl radical, electrophilic as shown by isomer ratios obtained in reaction with different aromatic and heteroaromatic compounds. Sources of thiazolyl radicals are few the corresponding peroxide and 2-thiazolylhydrazine (202, 209, 210) (see Table III-34) are convenient reagents, and it is the reaction of an alky] nitrite (jsoamyl) on the corresponding (2-, 4-, or 5-) amine that is most commonly used to produce thiazolyl radicals (203-206). The yields of substituted thiazole are around 40%. These results are summarized in Tables III-35 and IIT36. 

A second common example of the utility of INDO over CNDO is the methyl radical CH3. This planar molecule is a free radical with... 

Abbreviations for Ligand Names. Except for certain hydrocarbon radicals, for ligand (L) and metal (M), and a few with H, all abbreviations are in lowercase letters and do not involve hyphens. In formulas, the ligand abbreviation is set off with parentheses. Some common abbrevia-... 

For most vinyl polymers, head-to-tail addition is the dominant mode of addition. Variations from this generalization become more common for polymerizations which are carried out at higher temperatures. Head-to-head addition is also somewhat more abundant in the case of halogenated monomers such as vinyl chloride. The preponderance of head-to-tail additions is understood to arise from a combination of resonance and steric effects. In many cases the ionic or free-radical reaction center occurs at the substituted carbon due to the possibility of resonance stabilization or electron delocalization through the substituent group. Head-to-tail attachment is also sterically favored, since the substituent groups on successive repeat units are separated by a methylene... 

At the other end of the commonly encountered range we find the product rjr2 1. As noted above, this limit corresponds to ideal copolymerization and means the two monomers have the same relative tendency to add to both radicals. Thus if rj = 10, monomer 1 is 10 times as likely to add to Mj- than monomer 2. At the same time r2 = 0.1, which also means that monomer 1 is 10 times as likely to add to M2 than monomer 2. In this case the radicals exert the same influence, so the monomers add at random in a proportion governed by the specific values of the r s. 

Unsaturated Group Reactions. In addition to a comprehensive review of these reactions (16), there are excellent texts (17,18). Free-radical-initiated polymerization of the double bond is the most common reaction and presents one of the more troublesome aspects of monomer manufacture and purification. 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical (72—74) and radiation-initiated (75) polymerizations are also well known. At a constant temperature, the initial rate of the bulk or solution radical polymerization of acrylic monomers is first order with respect to monomer concentration and one-half order with respect to the initiator concentration. Rate data for polymerization of several common acrylic monomers initiated with 2,2 -azobisisobutyronittile (AIBN) [78-67-1] have been determined and are shown in Table 6. The table also includes heats of polymerization and volume percent shrinkage data. 

In general, acryUc ester monomers copolymerize readily with each other or with most other types of vinyl monomers by free-radical processes. The relative ease of copolymerization for 1 1 mixtures of acrylate monomers with other common monomers is presented in Table 7. Values above 25 indicate that good copolymerization is expected. Low values can often be offset by a suitable adjustment in the proportion of comonomers or in the method of their introduction into the polymerization reaction (86). 

Anionic extractants are commonly based on high molecular weight amines. Metal anions such as MnO or ReO can be exchanged selectively with inorganic anions such as Cl or The equiHbrium for a quaternary onium compound of organic radicals R for two anion species A and B ... 

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