Showing papers on "Hydrogen atom abstraction published in 1979"
176 citations
TL;DR: In this article, it was found that the rate constant for hydrogen abstraction from these compounds by t-BuO may be related to the number of secondary, allylic, and doubly allylic hydrogens in each molecule by the equation: kr= [0.072[Hsec] + 0.518[Hallylic] + 2.716[Hdoubly allyCL] x 106M-1 s-1.
Abstract: —
Laser photolysis techniques have been used to measure the reactivity of t-butoxy radical (t-BuO) toward various fatty acids. Eight compounds varying both in number and in the configuration of olefinic bonds were examined. It has been found that the rate constant for hydrogen abstraction from these compounds by t-BuO may be related to the number of secondary, allylic, and doubly allylic hydrogens in each molecule by the equation: kr= [0.072[Hsec] + 0.518[Hallylic] + 2.716[Hdoubly allylic] x 106M-1 s-1.
59 citations
56 citations
TL;DR: In this article, the rate constant for the reaction of methoxy radicals with oxygen was determined, independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride).
Abstract: Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110–160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction:
a value was determined of the rate constant for the reaction of methoxy radicals with oxygen:
is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k4 is given by the expression
In terms of atmospheric chemistry, this corresponds to a value of 105.6M−1·sec−1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 107.7M−1·sec−1 for k4. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3):
In particular k3 is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex.
48 citations
TL;DR: A/GRACE as mentioned in this paper is a system that generates elementary reaction networks for simple reactions including free radicals, ions and even active sites in heterogeneous catalysis, and also predicts the overall reaction rates and the product distributions in radical reactions in the gas phase where the Arrhenius parameters of elementary reactions are available.
Abstract: The system GRACE generates elementary reaction networks for simple reactions including free radicals, ions and even active sites in heterogeneous catalysis, and also predicts the overall reaction rates and the product distributions in radical reactions in the gas phase where the Arrhenius parameters of elementary reactions are available. In this paper, A/GRACE (part A of GRACE) is explained, which prepares elementary reaction networks for radical reactions. The reactant and the product are represented by square symmetric matrices. The off-diagonal elements represent bond multiplicity, or the number of localized electrons, between corresponding atoms, whereas the diagonal elements imply the number of unshared electrons on radical atoms. A reacting system, an ensemble of the participating molecules, is composed of atom groups, each of which consists of a center atom (usually non-hydrogen) and attached hydrogen atom(s), if any. Firstly, all the possible changes in the atom groups are selected, and the permit...
36 citations
TL;DR: In this article, the spatial distribution of trapped hydrogen atoms and methyl radicals in CH4 and CD4 irradiated at 4.2 K have been studied by ESR and it was shown that most of the hydrogen atoms are trapped within ∼16 A from each parent methyl radical forming distributed radical pairs.
Abstract: The spatial distributions of trapped hydrogen atoms and methyl radicals in CH4 and CD4 irradiated at 4.2 K have been studied by ESR. Most of the hydrogen atoms are trapped within ∼16 A from each parent methyl radical forming distributed radical pairs. This indicates that the thermalization distance of hydrogen atoms produced by 4.2 K radiolysis is ≲16 A in methane. Evidence has been obtained for the formation of a small amount of ĊH3...ĊH3 pairs, which are supposedly formed from hot hydrogen atom reactions. No evidence has been obtained for the formation of a pair of hydrogen atoms. There has been also obtained the experimental evidence that thermal hydrogen atoms unreactive with methane can abstract a hydrogen atom from ethane at 10–20 K. In the light of these results, the following conclusions are deduced: A part of hydrogen atoms produced in radiolysis of alkanes undergo hot abstraction to form very close alkyl radical pairs whereas the rest is thermalized and immobilized at the place close to each par...
36 citations
TL;DR: In this article, a photolysis of 6β-nitroso-oxy-5α-cholestan-3β-yl acetate gave the 19-oxime, 6β,19-oxide, 6-oxo-5β-choline-3 β-yl apetate, and 6 β-hydroxy-4-ene-3,17-dione.
Abstract: Photolysis of 6β-nitroso-oxy-5α-cholestan-3β-yl acetate gave the 19-oxime, 6β,19-oxide, 6-oxo-5α-cholestan-3β-yl apetate, and 6β-hydroxy-5α-cholestan-3β-yl acetate. The 6β.19-oxide was formed from the C-19 nitrosodimer by a novel photochemical reaction involving nitric oxide and with subsequent displacement of the presumed 19-diazonium salt by the 6β-hydroxy-function. The formation of ketone was coupled with the appearance of hyponitrous acid. The alcohol was formed by intermolecular hydrogen atom abstraction by the intermediate C-19 alkyl radical in a reaction not related to ketone formation. Evidence for the intermediacy of peroxynitrites in the formation of nitrate esters by nitrite photolysis under oxygen is presented. Hydroperoxides and nitrosyl chloride gave the derived nitrates. Attention is drawn to the formation of androst-4-ene-3,17-dione (59%) from reaction of trifluoroacetic anhydride and 17α-hydroperoxyprogesterone.
36 citations
TL;DR: In this paper, the hyperfine structure has been resolved for three nuclear spins which could be assigned by selective deuteration experiments: the nitrogen and meso-proton spin located in the guest-constituent of the complex and one proton spin originating from the CH 2 -group of a fluorene host molecule.
35 citations
TL;DR: In this article, the rate constants for quenching of oxalyl fluoride (3Au) molecules by selected classes of quenchers have been investigated using the technique of laser-induced time-resolved phosphorescence.
35 citations
TL;DR: In this article, the use of ONP to determine absolute signs of fine and hyperfine tensor elements in excited triplet states is developed theoretically and demonstrated experimentally, and convenient ONP-rules are formulated which relate the desired signs of the tensor element to quantities which can be extracted from the measured ONP field dependence.
35 citations
TL;DR: In this article, it is shown that DMPO can react with anionic radicals and that the resultant spin adducts are themselves highly dissociated, which is called the spin adduction of SO4−•.
Abstract: The •CO2− radical has been generated by photolysis of a solution of sodium peroxydisulfate containing sodium formate and by hydrogen abstraction using TiCl3 and H2O2 in the presence of sodium formate. In both cases, the inclusion of DMPO resulted in the formation of a spin adduct with aN = 15.8 G, aβH = 19.1 G, and g = 2.0058 which is assigned to the •CO2− adduct. In addition the DMPO adduct of SO4−• is presented. Finally, it is shown that DMPO can react with anionic radicals and that the resultant spin adducts are themselves highly dissociated.
TL;DR: In this paper, the authors studied the reactions of atoms with HCOND 2, CH 3 ND 2 and CH 2 OD with arrested relaxation infrared chemiluminescence and suggested that the origins of these differences lie in the dynamics of the attractive interactions exprinced by the F atom during the reaction.
TL;DR: In this paper, the free radical species observed by ESR and ENDOR spectroscopy were assigned molecular loci: a primary alkoxy radical at O6, a secondary alkoxy radicals at O2, a deprotonated hydroxyalkyl radical at C6, and a radical due to hydrogen abstraction at C5.
Abstract: Single crystals of α‐Methyl‐D‐glucopyranoside x irradiated at 77 K contain five free radical species observed by ESR and ENDOR spectroscopy. Four of these have been assigned molecular loci: a primary alkoxy radical at O6, a secondary alkoxy radical at O2, a deprotonated hydroxyalkyl radical at C6, and a radical due to hydrogen abstraction at C5. Structural considerations and mechanisms of formation are discussed.
TL;DR: The protonated iminyl (RArC) as mentioned in this paper is the most common hydrogen abstracting species in both cases of tetralone synthesis, unless trifluoroacetic acid is present.
Abstract: Tetralones can be synthesised by oxidation of phenylalkylideneamino-oxyacetic acids with persulphate. The iminyls formed initially abstract a γ-hydrogen from the alkyl chain and the resulting carbon radicals then cyclise onto the benzene ring. The same iminyls, when generated in benzene solution by thermolysis of imino-oxyperacetates, do not abstract γ-hydrogen unless trifluoroacetic acid is present. Hence, the hydrogen abstracting species in both cases is thought to be the protonated iminyl (RArC[graphic omitted]).
TL;DR: Arrhenius et al. as discussed by the authors investigated the reaction of methyl radicals with CCl4 and CCl3Br in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolyisation of di-tertiary butyl peroxide (dtBP) as the methyl radical sources.
Abstract: The reaction of methyl radicals with CCl4 and CCl3Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH3CCl3, formed via the combination of methyl and trichloromethyl radicals.
From these investigations Arrhenius parameters for the reactions
have been determined:
Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl4 and CCl3Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C2Cl6, and the HCl precursor CH3CCl3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl3Br and a chloromethane. Arrhenius parameters were obtained for the reactions
and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.
TL;DR: In this article, the authors show that adding any Lewis base to the alkenyltitanium intermediate induces decomposition of this intermediate to give an alkene by hydrogen atom abstraction from the medium, with loss of stereochemistry.
TL;DR: In this article, a model of electrochemical hydrogen ion discharge and hydrogen desorption processes (reactions I and II, respectively) is developed which combines the principal features of the Marcus-Levich-Dogonadze theory of electron transfer in a polar medium.
Patent•
20 Aug 1979
TL;DR: In this paper, the authors defined a class of compounds with antitumoral activity corresponding to the formula (I): (I) where R'1 is a hydrogen atom or an alkoxy, acyl, formyl or haloacyl radical; (II) wherein R'2 and R'3 are a hydrogen atoms or an alkyl radical, and together are a carbonyl group.
Abstract: Compounds with antitumoral activity corresponding to the formula (I): ##STR1## wherein R'1 is a hydrogen atom or an alkoxy, acyl, formyl or haloacyl radical; R'2 is a hydrogen atom or an alkyl radical; R'3 and R"3 are a hydrogen atom, hydroxyl radical or an alkanoyloxy radical, and together are a carbonyl group, and R'3 and R'5 together are an epoxy bridge or a double bond; R'4 is a hydrogen atom or an alkyloxycarbonyl, hydroxymethyl, alkanoyloxymethyl or acetamido radical; R'5 and R"5 are a hydrogen atom or a hydroxyl, alkanoyloxyl, ethyl or 2-hydroxyethyl radical; R'6 is a hydrogen atom or an ethyl, 2-hydroxyethyl or acetyl radical; R1 is a hydrogen atom or an alkyl, formyl or acyl radical; R2 is a hydrogen atom or alkoxy radical; R3 is a hydrogen atom or a hydroxyl or alkanoyloxyl radical, and together with R4 is an epoxy bridge or a double bond; R4 is a hydrogen atom or a hydroxyl, alkanoyloxyl radical, and together with R5 is an epoxy bridge; R6 is an alkyloxycarbonyl, hydrazido, acetamido, hydroxymethyl or alkanoyloxymethyl radical; and R5 and R7 are a hydrogen atom or a hydroxyl and alkanoyloxyl radical; acid addition and quaternary ammonium salts thereof and 12-chloro derivatives thereof.
TL;DR: In this article, a mechanism for the photochemical transformation of xanthione is proposed which features a primary photochemical step involving hydrogen abstraction from the solvent and the formation of a solvent-caged radical pair.
TL;DR: In this paper, reaction rate coefficients and product ion distributions have been measured for the reaction of Ne + with H 2, N 2, CO +, H 2 O, CH 4 and CH 3 Cl at 300 K using a selected ion flow tube (SIFT) apparatus.
TL;DR: In this article, a simple technique for the determination of tert-butoxy endgroups in poly(methyl methacrylate) and polystyrene was devised, which is based on cleavage of the tertbutyl ether with boron trichloride and analysis of the resulting tert-Butyl chloride by gas-liquid chromatography.
Abstract: A simple technique has been devised for the determination of tert-butoxy endgroups in poly(methyl methacrylate) and polystyrene. The method is based on cleavage of the tert-butyl ether with boron trichloride and analysis of the resulting tert-butyl chloride by gas-liquid chromatography. In polystyrene, tert-butoxy endgroups were also determined by dealkylation with trifluoroacetic acid, followed by reaction of the resulting hydroxy endgroups with o-sulfobenzoic anhydride and analysis for sulfonate by the dye-partition technique with methylene blue reagent. From these analyses it was possible to conclude that tert-butoxy radicals, derived from the decomposition of di-tert-butyl peroxalate (DBPOX), initiated styrene polymerization largely by direct addition, whereas in their reaction with methyl methacrylate (MMA) both direct addition and hydrogen abstraction from the monomer were important processes. The extent of hydrogen abstraction was determined from the yield of tert-butanol in the reaction o...
TL;DR: In this article, the photo-induced reaction of CpFe(CO)₂Me (1a) and diphenylacetylene in solution gives metallocyclic derivatives containing either one or two Diphenylbutadienyl units.
Abstract: Photolysis of CpFe(CO)₂R complexes [R = Me (1a), Et (1b), Ph (1c)] in hydrocarbon solvents results in loss of the group R and formation of the binuclear compound [CpFe(CO)₂]₂ (2). In the case of 1a, the photogenerated methyl group reacts to give methane by intramolecular hydrogen abstraction from the Cp ring, or by intermolecular hydrogen abstraction either from the solvent or another methyl group. The photoinduced dealkylation of the ethyl compound 1b is explained by β-elimination (to give ethylene) and subsequent reaction of the hydrido intermediates thus formed with unchanged 1b (to give ethane). The photolysis of 1c leads to phenyl groups which abstract hydrogen from the solvent to give benzene; a noticeable amount of diphenyl is also observed if benzene is used as a solvent.In the presence of potential two-electron ligands L [L = PMe₃, P(OMe)₃], only the carbonyl groups of CpFe(CO)₂Me (1a) are photolabile, and substituted derivatives of the type CpFe(CO)(L)Me [L = PMe₃ (3a), P(OMe)₃ (4a)] and CpFe(L)₂Me [L = P(OMe)₃ (5a)] are formed.The photoinduced reaction of CpFe(CO)₂Me (1a) and diphenylacetylene in solution gives metallocyclic derivatives containing either one or two diphenylacetylene units. On the basis of the IR, the ¹H and ¹³C NMR, and the mass spectra, the complex CpFe(CO)(Ph₂C₂-COMe) (6a) is assigned a structure containing a vinyl-ketone unit in a five-membered metallocycle, while in CpFe(Ph₄C₄-COMe) (7a) a tetraphenylbutadienyl group appears to be incorporated into a seven-membered metallocycle
TL;DR: The values of the Bronsted exponent for several examples of nucleophilic substitution reactions, aromatic electrophilic substitution reaction, and hydrogen atom abstraction from toluene by free radicals have been calculated from the ρ values of corresponding reactions as mentioned in this paper.
Abstract: The values of the Bronsted exponent for several examples of nucleophilic substitution reactions, aromatic electrophilic substitution reactions, and hydrogen atom abstraction from toluene by free radicals have been calculated from the ρ values of the corresponding reactions. The magnitude of the Bronsted exponent is shown to indicate the degree of charge developed in the transition state structure.
TL;DR: In this paper, the rate constant of hydrogen abstraction by the n, π* triplet state of poly(4-vinylbenzophenone) from tetrahydrofuran was compared with that of benzophenone (BP) in benzene solution at 25°C, the former being about twice as large as the latter.
Abstract: The rate constant of hydrogen abstraction by the n, π* triplet state of poly(4-vinylbenzophenone) (PVBP) from tetrahydrofuran was compared with that of benzophenone (BP) in benzene solution at 25°C, the former being about twice as large as the latter. The electronic behavior of the triplet BP group in the polymer was investigated by T—T absorption and phosphorescence, being the same as that of BP. A well-resolved ESR spectrum of the diphenylamino radical was detected upon UV irradiation of a benzene solution of PVBP and diphenylamine (DPA) and its concentration was compared with that of the poly(vinylbenzophenone-co-methyl methacrylate)—DPA or BP—DPA system. The concentration decreased in the order: PVBP>copolymer>BP. The polymer effect on the rate constant and the radical formation was explained in terms of the increase in the reaction efficiency on account of energy migration along the side chain of the polymer.
TL;DR: In this article, the relative reactivities of phenyl, p-chlorophenyl, and p-nitrophenyl radicals, derived from arylazotriphenyl-methane, towards chlorine abstraction from carbon tetrachloride, were estimated from the results of the competitive reaction of the radicals with carbon-to-oxide and iodine, assuming that the rate of scavenging by the radicals by iodine is almost invariant.
Abstract: The relative reactivities of phenyl, p-chlorophenyl, and p-nitrophenyl radicals, derived from arylazotriphenyl-methane, towards chlorine abstraction from carbon tetrachloride were estimated from the results of the competitive reaction of the radicals with carbon tetrachloride and iodine, assuming that the rate of scavenging of the radicals by iodine is almost invariant, irrespective of the substituent on the radical. On the basis of the results, the relative reactivities of these radicals in other elementary reactions such as hydrogen abstraction, bromine abstraction, addition to benzene or allyl sulphide, and SH2 displacement on disulphide were estimated. These data show that p-chloro- and p-nitro-phenyl radicals are more reactive than phenyl towards electron-donating substrates and less reactive towards elecron-accepting substrates.