Radical mechanism, for the reaction

A new class of organic NF compounds, N-fluoroazoxy compounds, has recently been reported. Trifluoronitrosomethane reacts with N2F4 under the influence of light or heat to form N-fluoro-N -trifluoromethyldiazine-N -oxide (III) (6). A free radical mechanism for the reaction was proposed and it was sug-... 

Other mechanisms of insertion than the type shown in Eqs. (c) and (d) may exist, ESR evidence, for example, supports a radical mechanism for the reaction of alkyl-platinum complexes with olefins . 

It follows that, when the values of and V IF q corresponding to the different experiments are substituted in Eq. (c) or Eq. (d) k becomes a function of n only for each experiment. The point of intersection of the k versus n curves should give the value of k at the temperature considered and the unique value of n. This is shown in Fig. 5 for 750 C. The order is found to be 1.5, also at 730° and 710°C. This order is quite plausible on the basis of radical mechanisms for the reaction. The values of k are given in Table 1. The Arrhenius diagram for k is shown in Fig. 6. 

The authors suggest a radical mechanism for the reaction, in which a singleelectron transfer from CAN to the P-keto esters and latter radical adds to the imine intermediate (Scheme 8.32). 

FIGURE 4 21 The initiation and propagation steps in the free radical mechanism for the chlorination of methane Together the two propaga tion steps give the overall equation for the reaction... 

The elementary steps (1) through (3) describe a free-radical chain mechanism for the reaction of an alkane with a halogen. 

Problem 7.19 Oik- of the chain-termination steps that sometimes occurs to interrupt polymerization is the following reaction between two radicals. Propose a mechanism for the reaction, using fishhook arrows to indicate electron flow. 

SCHEME 6. Suggested radical/anion-radical pair mechanism for the reaction of a-sulfonyl carban-ions with perhaloalkanes (CC14 as the example)553, R" = R3S02CR1R2, k2> > k. ... 

A second theoretical inconsistency with a radical mechanism for the biochemical reaction was described by Finke. Although cleavage of the methyl-Co(II) bond is very efficient and rapid process, he argued that homolysis of methyl-Co does not occur in enzymes because reduction of CHs-Co requires too low a potential for biochemically relevant electron donors (<-1.0 V vs NHE) (195). For example, the mid-... 

The reactions of oxygen with metal-alkyl derivatives typically involve radical intermediates (73, 74), and a likely mechanism for the reactions of [TpBut]MgR with 02 is illustrated in Scheme 6. Specific... 

FIGURE 6.6 Hypothetical radical mechanism for the formation of 5a-a-tocopheryl henzoate (11) hy reaction of a-tocopherol (1) with dibenzoyl peroxide. 

The question of rearrangement in acyloxy radicals is still unsettled. In the case of the decomposition of -methoxy- -nitrobenzoyl peroxide rearrangement is observed, but the other circumstances indicate a polar mechanism for the reaction.118... 

Two radicals (OH and H ) are produced from the reaction of one radical (O ). This allows the reaction rate to increase without limit if it is not balanced by corresponding radical-destruction processes. The result is a runaway reaction or explosion. This can be demonstrated by consideration of the following simplified chain mechanism for the reaction A +. ..- P. 

Further supporting evidence for the occurrence of diradicals was obtained by Reich and Cram when they heated [2.2]paracyclophane with either dimethyl maleate or fumarate esters at 200 °C for 40 h in the absence of air. The cis- and trans-2,3-dicarboxymethyl[4.2]paracyclophanes 162 and 163 were formed in about equal amounts, irrespective of the configuration of the olefin employed. Other similar reactions would also suggest a radical mechanism for this reaction furthermore, a concerted addition of the olefinic double bond to 2, or to the postulated intermediate diradical 157, can be ruled out because of lack of stereospecificity of insertion. 

A free-radical mechanism has been suggested for the nitrosation of 1,2-phenylenediamine (22) by peroxynitrite PN/CO2. 1,2,3-Benzotriazole (26) was formed as a result of an intramolecular nucleophilic displacement on the diazo hydroxide (25) by the neighbouring amine group. The authors suggest that the mechanism involves an initial H-atom abstraction or one-electron oxidation from (22) by CO3 , followed by the reaction of the product (23) with NO. The inhibitory effects of azide support a free-radical mechanism of the reaction. 

Hatakeyama, S., N. Washida, and H. Akimoto, Rate Constants and Mechanisms for the Reaction of OH(OD) Radicals with Acety-... 

Jolly, G. S P. J. McKenney, D. L Singleton, G. Paraskevopoulos, and A. R. Brossard, Rate Constant and Mechanism for the Reaction of Hydroxyl Radical with Formic Acid, 90, 6557-6562... 

These results lead to a general mechanism for the reaction nitrenium ions with aromatic compounds (Fig. 13.71). Initial encounter leads to a 7i-complex (141). The latter is converted into isomeric a complexes (142-144) which, in turn, either tau-tomerize to give stable adducts (145-147) or else dissociate to give radicals. The relative rates of these processes depend on the reactivities of the nitrenium ion and the arene. With less reactive nitrenium ions the 7i-complex is relatively long lived. With more reactive nitrenium ions the n complex forms in a low steady-state... 

The stable free radical nitric oxide (NO) has an important role as a biological messenger. The reaction of NO with superoxide (O2 ) forms the powerful oxidant peroxynitrite (ONOO ), and a mechanism for the reaction of ONOO resulting in the abstraction of H from C—H bonds is shown (equations 109, 110). The formation of HO from the spontaneous decomposition of peroxynitrite, and of COJ radicals from CO2 catalyzed decomposition of peroxynitrite, have been demonstrated. ... 

Problem 16.20 Suggest a typical free-radical mechanism for the Hunsdiecker reaction which requires the initial formation of an acyl hypobromite. RC—OBr, from the Ag salt and Br,. ... 

The effect of the hydroxyl radical (HO ) on luminol chemiluminescence has also been intensively studied178 187 198 199. Although detailed mechanisms for the reaction of hydroxyl radicals with hydrazides remain unknown, two different processes are assumed to be involved oxidation of the hydrazide group and addition of hydroxyl radical to the aromatic ring (Scheme 19)180 1". 

A recent theoretical study by Takeuchi et al. [140] has examined the mechanism for the reaction of both alkenes and alkynes with the H-terminated silicon surface using periodic DFT calculations, and the results are in good agreement with the proposed radical-based mechanism [137]. In particular, the calculations show that the reaction occurs through a carbon-based radical intermediate which must be sufficiently stabilized to proceed by abstraction of a surface hydrogen (as in the case of styrene) if the intermediate is not stable enough, it will preferentially desorb (as in the case of ethylene). The calculations also show that reaction with terminal alkynes should proceed faster and lead to more stable products than with terminal alkenes [140]. 

Based on the analysis of the reactions in Scheme 3 and on previous studies (46, 47), a mechanism for the reaction was proposed in which the /x-peroxo complex, 16, may simultaneously abstract two hydrogen atoms from iso-propyl groups on the pyrazolyl ligands. Alternatively, because of the weak 0—0 bond, 16 may homolytically dissociate to form two Tp"Co(0-) oxo-radical moieties, and these species would then abstract hydrogen from the iso-propyl groups. In either case, the resulting carbon-centered radical can either react with solvent, as was observed for the Tp complex (46), or with another carbon-centered radical so as to regenerate the Tp"Co(OH) complex and produce a derivative of the Tp" complex with an iso-propenyl substituent, 18. Ultimately, either route would produce the (/x-OH)2 complex, 17. 

Write a possible mechanism for the reaction, showing the propagation steps with (CH3)3CO as the chain-propagating radical. Use the bond-dissociation energies of Table 4-6 to determine whether your mechanism is energetically and kinetically feasible. Assume the O-CI bond-dissociation energy of fert-butyl hypochlorite is 61 kcal mole-1. 

The H- radical reaction with the parent compound (16c) is a likely explanation for the lower decomposition temperatures in H2 relative to N2 (119-121). The exact mechanism for the reaction of H with Ga(CH3)3 is not known, but the experimentally observed acceleration is also predicted by simulations of Ga(CH3)3 decomposition based on a detailed kinetics mechanism for GaAs growth (122). The effect of H will change with pressure and residence time, and this variation may explain the observation of only minor differences in decomposition temperatures at low pressures and short residence times (118). 

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