Reactions of halogen oxides studied by flash photolysis II. The flash photolysis of chlorine monoxide and of the ClO free radical

1971 ◽  
Vol 323 (1554) ◽  
pp. 401-415 ◽  
Keyword(s):  
Free Radical ◽  
Quantum Yield ◽  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Vibrationally Excited ◽  
Chlorine Atoms ◽  
Chlorine Monoxide ◽  
Halogen Oxides ◽  
Excited Oxygen

A study of the flash photolysis of chlorine monoxide and of its photosensitized decomposition by chlorine and bromine has yielded rate constants for the reactions Cl + Cl 2 O → Cl 2 + ClO, k 1 = 4.1 x 10 8 l mol -1 s -1 , Br + Cl 2 O → BrCl + ClO, k 9 = 6.1 x 10 8 l mol -1 s -1 , ClO + Cl 2 O → ClO 2 + Cl 2 , k 3 = 2.6 x 10 5 l mol -1 s -1 , ClO + Cl 2 O → Cl 2 + O 2 + Cl, k 4 = 6.5 x 10 5 l mol -1 s -1 , 2ClO → Cl 2 + O 2 , k 2 = 2.8 x 10 7 l mol -1 s -1 . The quantum yield for the decomposition of chlorine monoxide was measured in each of the three systems and is quantitatively accounted for by the reactions given. The CIO free radical has been flash photolysed and the production of vibrationally excited oxygen in the reaction O + CIO → Cl + O* 2 ( v" ≼ 14), k 11 = 7.5 x 10 9 l mol -1 s -1 demonstrated. The same reaction is responsible for the production of O* 2 in the flash photo­lysis of Cl 2 O with radiation below ~ 300 nm. The relaxation of O* 2 by chlorine atoms is exceptionally efficient, with a rate constant for v" = 12 in excess of 2 x 10 9 l mol -1 s -1 . The corresponding rate constant for relaxation by Cl 2 O is < 10 8 l mol -1 s -1 .

Reactions of halogen oxides studied by flash photolysis. I. The flash photolysis of chlorine dioxide

1971 ◽  
Vol 323 (1552) ◽  
pp. 29-68 ◽  
Keyword(s):  
Chlorine Dioxide ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Vibrationally Excited ◽  
Extinction Coefficients ◽  
Chlorine Monoxide ◽  
Vibrational Levels ◽  
Halogen Oxides ◽  
Excited Oxygen

The production and decay of the CIO radical and of vibrationally excited oxygen following the isothermal flash photolysis of chlorine dioxide has been studied. From their dependence on flash energy and from the effects of added chlorine, oxygen and chlorine monoxide on the system, the following mechanism and rate constants are proposed: CIO 2 + hv → CIO + O 2CIO → CI 2 + O 2 K 1 = 2.7 x 10 7 l mol -1 s -1 O + CIO 2 → CIO + O 2 * ( v " ≼ 15) k 3 = 3.0 x 10 10 l mol -1 s -1 O + CIO → CI + O 2 * ( v " ≼ 14) k 4 = 7.0 x 10 9 l mol -1 s -1 CIO (CIO 2 ) + O 2 * ( v " = n ) → CIO (CIO 2 ) + O 2 * ( v " < n ) k 10 ( v " = 12) = 2 x 10 8 l mol -1 s -1 CI + O 2 * ( v " = n ) → CI + O 2 * ( v " < n ) k 11 ( v " = 12) = 7 x 10 9 l mol -1 s -1 O + O 2 * ( v " = n ) → O + O 2 * ( v " < n ) k 12 ( v " = 12) = 2 x 10 10 l mol -1 s -1 O + Cl 2 O → 2CIO k 6 = 5.2 x 10 9 l mol -1 s -1 The rate constants k 10 , k 11 and k 12 for O 2 * (v" = 6) and the relative values of k 3 for various vibrational levels have also been measured. Studies of the flash photolysis of mixtures of chlo­rine monoxide and chlorine dioxide and of chlorine and oxygen have yielded values of k 1 in agreement with that given above. The extinction coefficients of the CIO radical at 257.7, 277.2 and 292 nm were found to be 1150, 1700 and 1050 l mol -1 cm -1 respectively.

Reactions of halogen oxides studied by flash photolysis IV. Vacuum ultraviolet kinetic spectroscopy studies on chlorine dioxide

1974 ◽  
Vol 336 (1607) ◽  
pp. 495-505 ◽  
Keyword(s):  
Vacuum Ultraviolet ◽  
Flash Photolysis ◽  
Vibrational Energy ◽  
Heat Of Reaction ◽  
Rydberg Series ◽  
Vibrationally Excited ◽  
Extinction Coefficients ◽  
Spectroscopy Studies ◽  
Halogen Oxides ◽  
Excited Oxygen

The rate constants for the production of vibrationally excited oxygen in the reactions O + CIO 2 -----» O 2 (v''≤ 15) + CIO O + CIO -----» O 2 (v''≤ 14) + Cl are approximately equal for all values of v" ≤ 13. The oxygen initially receives 45+10% of the heat of reaction in the form of vibrational energy. Extinction coefficients have been measured for several bands of the C-X, D -X and E -X systems of CIO 2 in the vacuum ultraviolet. Five new systems are reported between 141 and 128 nm. Two of these, F-X and J-X , and the C-X system form a Rydberg series for an ionization potential of 10.36 eV.

Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)

1983 ◽  
Vol 61 (5) ◽  
pp. 801-808 ◽  
Author(s):  
Yuan L. Chow ◽  
Gonzalo E. Buono-Core ◽  
Bronislaw Marciniak ◽  
Carol Beddard
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Decay Rates ◽  
Polynuclear Aromatic Hydrocarbons ◽  
Aromatic Ketone ◽  
Quantum Yields ◽  
Triplet States ◽  
Quenching Rate ◽  
Triplet Energy

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2021 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

Absolute rate constants for hydrocarbon autoxidation. 33. A product study of the self-reaction of α-tetralylperoxyls in solution

1983 ◽  
Vol 61 (9) ◽  
pp. 2037-2043 ◽  
Author(s):  
A. Baignée ◽  
J. H. B. Chenier ◽  
J. A. Howard
Keyword(s):  
Steady State ◽  
Free Radical ◽  
Rate Constant ◽  
Rate Constants ◽  
The Self ◽  
Absolute Rate ◽  
Chain Reaction ◽  
Low Concentrations ◽  
A Chain ◽  
Product Study

The major initial products of the self-reaction of α-tetralylperoxyls (C10H11O2•) in chlorobenzene at 303–353 K are equal concentrations of α-tetralol and α-tetralone in ~90% yield based on the number of initiating radicals. These yields are consistent with the non-radical (Russell) mechanism for self-reaction. Low concentrations of bis(α-tetralyl) peroxide are produced, indicating that there is a small but detectable free-radical contribution towards termination. C10H11O2• undergoes β-scission in this temperature range but steady-state concentrations of C10H11• are too low to influence the termination rate constant 2kt, or react with C10H11O2• to give (C10H11O2. α-Tetralol to α-tetralone ratios and total yields of these products are significantly less than 1 and 100%, respectively, in methanol and acetonitrile. Formaldehyde is produced in methanol indicating the involvement of α-hydroxymethylperoxyls, derived from the solvent, in termination. There is no evidence for a chain reaction or a zwitterion intermediate for self-reaction of C10H11O2• in solution.

The nature of the transition state in diarylmethyl cation – nucleophile combination reactions as probed by secondary α-deuterium isotope effects

2001 ◽  
Vol 79 (12) ◽  
pp. 1887-1897
Author(s):  
Thuy Van Pham ◽  
Robert A McClelland
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Bond Formation ◽  
Kinetic Isotope ◽  
Rate Limiting

Transition-state structures for the carbocation–nucleophile combination reactions of (4-substituted-4'- methoxydiphenyl)methyl cations with water, chloride, and bromide ions in acetonitrile–water mixtures have been investigated by measuring the secondary α-deuterium kinetic and equilibrium isotope effects. Rate constants in the combination direction were measured with laser flash photolysis. Equilibrium constants were measured for the water reaction by a comparison method in moderately concentrated sulfuric acid solutions, for the bromide reaction via the observation of reversible combination, and for the chloride reaction from the ratio of the combination rate constant and the rate constant for the ionization of the diarylmethyl chloride product. The fraction of bond making in the transition state has been calculated as the ratio log (kinetic isotope effect):log (equilibrium isotope effect). For the water reaction, there is 50–65% bond making in the transition state; this is also true for cations that are many orders of magnitude less reactive. The same conclusions, 50–65% bond formation in the transition state independent of reactivity, have previously been made in correlations of log kw vs. log KR. Thus, two quite different measures of transition structure provide the same result. The kH:kD values for the halide combinations in 100% acetonitrile are within experimental error of unity. This is consistent with suggestions that these reactions are occurring with diffusional encounter as the rate-limiting step. Addition of water has a dramatic retarding effect on the halide reactions, with rate constants decreasing steadily with increased water content. Small inverse kinetic isotope effects are observed (in 20% acetonitrile:80% water) indicating that carbon—halogen bond formation is rate-limiting. Comparison of the kinetic and equilibrium isotope effects shows ~25 and ~40% bond formation in the transition states for the reactions with bromide and chloride, respectively.Key words: carbocation, isotope effect, transition state, halide.

Energy disequilibrium in the flash photolysis of NO 2

1973 ◽  
Vol 334 (1599) ◽  
pp. 553-568 ◽  
Keyword(s):  
Nitric Oxide ◽  
Flash Photolysis ◽  
Vibrational Energy ◽  
Dissociation Limit ◽  
Primary Process ◽  
Transfer Energy ◽  
Vibrationally Excited ◽  
Absolute Concentrations ◽  
The Absolute ◽  
Excited Oxygen

From measurements of the absolute concentrations of vibrationally excited oxygen produced in levels v" = 4 to v" = 13, it is concluded that ca . 20 % of the exothermicity of the reaction O( 3 P) + NO 2 → NO + O + 2 ( v" ≤11) (1) appears initially as vibrational energy in oxygen. Vibrationally excited nitric oxide ( v" = 1, 2) is also observed and may be produced in this reaction or in the primary process NO 2 + hv → NO ( v" ≤ 2) + O( 3 P). More highly excited oxygen ( v" ≤ 15), with energy exceeding the exothermicity of the reaction, is produced in reaction (1) when the NO 2 is first excited by radiation above the dissociation limit near 400 nm. The excited NO 2 thus produced can also transfer energy to nitric oxide. NO 2 * + NO( v" = 0) → NO 2 + NO( v" = 1).

The flash photolysis of chlorine monoxide

1957 ◽  
Vol 243 (1232) ◽  
pp. 24-32 ◽  
Keyword(s):  
Chlorine Dioxide ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Reaction Scheme ◽  
Inert Gas ◽  
Short Chain ◽  
Large Excess ◽  
Straight Chain ◽  
Chain Reaction ◽  
Chlorine Monoxide

The flash photolysis of chlorine monoxide in a large excess of inert gas yields chlorine and oxygen, the normal products of photolysis, accompanied by measurable quantities of the ClO radical as an intermediate. The normal and chlorine-sensitized decompositions of chlorine monoxide are studied and a reaction scheme is proposed for the system which has the character of a short-chain reaction with CIO and CI acting as chain carriers. By a study of the decay of the CIO radical and the formation of chlorine dioxide, rate constants are derived for the CIO decay, the production of chlorine dioxide and the straight-chain decomposition of chlorine monoxide by the CIO radical.

Photochemical reduction of potassium chromate solubilized with 18-crown-6 in chloroform

1984 ◽  
Vol 49 (2) ◽  
pp. 398-403 ◽  
Author(s):  
Jana Muchová ◽  
Vladislav Holba
Keyword(s):  
Quantum Yield ◽  
Temperature Coefficient ◽  
Rate Constant ◽  
Rate Constants ◽  
Decomposition Reaction ◽  
Potassium Chromate ◽  
Photochemical Reduction ◽  
Chromate Ions ◽  
Mechanism Of The Reaction

The cyclic polyether 18-crown-6 was used as solubilizer to obtain a solution of potassium chromate in chloroform. While perfectly steady in darkness, the solution decomposes under the action of light. The decomposition reaction was monitored by measuring the decrease in the absorbance of chromate ions, and the rate constants, the temperature coefficient of the rate constant, and the quantum yield were determined. The mechanism of the reaction is discussed.

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