H atom abstraction reaction

The formation of adduct is followed by fragmentation and subsequent H-atom abstraction reaction from the sulfinic acid produced. Strong acid solutions of aromatic sulfoxides like thianthrene 5-oxide (7) or phenothiazine 5-oxide (8) gives rise to ESR signals, which... 

The chemical reactivity of the organoruthenium and -osmium porphyrin complexes varies considerably, with some complexes (M(Por)R2, M(Por)R and Os(OEP)(NO)R) at least moderately air stable, while most are light sensitive and Stability is improved by handling them in the dark. Chemical transformations directly involving the methyl group have been observed for Ru(TTP) NO)Me, which inserts SO2 to form Ru(TTP)(N0) 0S(0)Me and Ru(OEP)Me which undergoes H- atom abstraction reactions with the radical trap TEMPO in benzene solution to yield Ru(OEP)(CO)(TEMPO). Isotope labeling studies indicate that the carbonyl carbon atom is derived from the methyl carbon atom. "" Reaction of... 

The mechanism of H2 formation involves both unimolecular H2 elimination, when both of the H atoms of a hydrogen molecule originate from the same alkane molecule, and H atom elimination with subsequent H atom abstraction reaction. We show the mechanism on the example of cyclohexane photolysis hv = 7.6 eV) [91] ... 

Some Representative Arrhenius Parameters for the H-Atom Abstraction Reactions of CH3 Radicals CHS + R—H — CHi + R... 

The various disulfur species (HSSH, SSH, S2) are partially equilibrated with each other through a number of H atom abstraction reactions, for example, ... 

Thus, the eventual products of the two pathways (la) and (lb) by which OH reacts with DMS under atmospheric conditions have not yet been fully established. However, circumstantial evidence, namely the 70% yield of SO2 in the study of Barnes et al. (21) being roughly equal to the branching ratio for the H-atom abstraction (reaction (la)) at 298 K determined by Hynes et al. (12), indicates that S02 is a major product of the abstraction reaction and that DMSO, DMSO and MSA probably result from the primary addition of OH to the sulfur atom (reaction (lb)). 

The stationary points of H-atom abstraction reactions of triplet CF2 with XH (n = 1-4 X = H, F, Cl, Br, O, S, N, P, C, and Si) were computed using UCCSD(T) methods with 6-311++G(3df,2p) and aug-cc-pVTZ basis sets.56 Covalent surface... 

The large Einstein radiative coefficients [225] and the widely spaced vibration-rotation quantum states make HF peculiarly prone to stimulated emission, and a large proportion of the chemical lasers which have been reported operate on lines in the infrared bands of this molecule [224], H-atom abstraction reactions by F and F-atom abstraction by H are both normally exothermic, and HF is quite generally produced in a vibrational distribution giving rise to oscillation. However, the systems are complex frequently both types of reaction occur, and the details of the vibrational distribution resulting from chemical reaction are difficult to evaluate. 

Chemical Reactions. Both 1(n, n ) and 3(n, n ) states of carbonyl compounds are chemically reactive, as indicated by intramolecular H-atom abstraction reactions (e.g., Norrish type II), intramolecular rearrangement giving oxacarbenes in cyclic ketones (see ref. 245), intermolecular H-atom abstraction reactions, and photocycloadditions to olefins to form oxetanes in solution ... 

This method is predicated on the assumptions that an appropriate scavenger added to the system simply inhibits the H-atom abstraction reaction 25 and that the sum of = 1.00. Obviously,... 

The formation of an olefin by the Norrish type II photoelimination was not much affected by the presence of an unconjugated olefinic group, but the formation of propylene (and acrolein) in 5-hexenal requires a new photochemical transformation mechanism. It has been suggested that an olefinic, triplet precursor which can undergo intramolecular H-atom abstraction reaction is responsible for this process. 

Detailed studies of H-atom abstraction reactions of cyclopropyl diketones U1), 2,2,5,5-tetramethyltetrahydrofuran-3-4-dione 130) cycloalkanediones57) and substituted benzils 121 , among others, have appeared. The cyclopropyl diketones reacted normally via semidione radicals without ring enlargement. 

Hydroxyl radicals ( OH) are powerful oxidants and participate in a number of reactions such as addition to the double bonds forming radical adducts, electron transfer reactions, and H-atom abstraction reaction. The rate constants for the reaction of OH radicals with organic substrates are mostly diffusion controlled (10 -10 ° M" s" ). When OH radical reacts with cellular organic molecules (RH) either by hydrogen abstraction [Eq. (4)] or by addition reaction, it leaves a radical site on the molecule (R ) and sometimes these radicals can add to the oxygen present in the cells, to be converted to peroxyl radicals [ROO, Eqs. (4) and (5)]. Rate constants for these reactions vary between 10 to diffusion-controlled limits depending on the nature and substitution on RH. °... 

Besides direct reaction of atomic oxygen with a stable hydrocarbon, another path to an oxide radical on the surface was thought to be reaction of O atoms, from the gas-phase or on the surface, with hydrocarbon radicals formed from the initial H-atom abstraction reaction ... 

Even if it does not occur very readily, alkylperoxy radical isomerization may play an important part because the decomposition products, which include aldehydes, lead to propylhydroperoxide via H atom abstraction reactions of appreciably lower activation energy, for example. 

As discussed in Section 1.16, the competing reaction to alkylperoxy radical formation, (8) and (9), is the H atom abstraction reaction... 

Here, M represents a third body solvent molecule, which is an acceptor of an excess energy released in each three-body recombination reaction. Hydrogen atoms in reactions (7.3) and (7.4) must be supplied from either photodissociation of solvent or H-atom abstraction reaction from solvent. 

SCHEME 11.8 Common mechanisms of C—H activation (after the initial complex, the + n charge is indicated only in cases where overall charge of the complex is altered during the reaction pathway). The metalloradical and ligand-based H-atom abstraction reactions (both shown on the left-hand side) are not discussed herein. 

The radical anion O- when produced in the gas phase is characterised by high reactivity for H-atom abstraction reactions and the species formed by the above reactions react rapidly in this manner with H2, NH3, CH3OH, CH4. It has been proposed that the reaction with H2 produces H-atom-like species which are active for H2/D2 exchange. 

The location of 02 addition in the product shown above is that most favored energetically (Andino et al. 1996). The H-atom abstraction reaction to yield phenolic compounds, such as o-cresol, has been shown to be relatively minor, accounting for 16% of the overall OH radical mechanism for toluene (Calvert et al. 2002). The N02 reaction of the OH adduct leads to nitroaromatics ... 

Figure 3 Surprisal plots (18) for the HF vibrational state distribution from the exoergic H atom abstraction reaction F + (CH,)4C - (CH,),CCH2 + HF(v). (Bottom panel) The observed (by D. J. Bogan and D. W. Setser, J. Chem. Phys. 64 586 (1976)) distribution, P(v), open dots connected by a line, and the (so called, prior) distribution, P (v) full symbols, vs. the HF vibrational energy. The prior distribution is the one expected when all products final states are equally probable (18). The observed distribution is qualitatively different from the prior one and their deviance, the surprisal, —In(P(v)/P"(v)) is plotted vs. E/Ev, where Ev is the HF vibrational energy and E is the total energy, in the upper panel. One can interpret the linear dependence of the surprisal on the HF vibrational energy as reflecting the presence of a quantity which is conserved by the dynamics. (See, for example, ref. (108)). In this sense, surprisal analysis is analogous to the search for quantum numbers that are not destroyed by the intramolecular couplings.

Just as in the case of the pyrimidines, OH-radical attack is by addition to a ring double bond targeting a carbon atom (but not the guanine carbonyl carbon), to the practical exclusion of H-atom abstraction reactions. However in the purines, the relative importance of the target sites is more difficult to assess for two reasons. First, the five (adenine) or four (guanine) OH-adducts that are formed in reactions (64)-(72) do not show a pronounced difference in their redox behaviour as the two (for each) pyrimidine-derived ones do. 

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