Effect of deuterium iodide and hydrogen bromide on the photo-oxidation of methyl iodide

Farren, J.; Gilbert, James R.; Linnett, J. W.; Read, I. A.

doi:10.1039/tf9646000740

Cited by 11 publications

(10 citation statements)

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“…Reference 40 is a relative measurement of CH 3 + HBr with CH 3 + I 2 , while ref is an absolute measurement near 300 K of CH 3 + I 2 . This value derived from the two is in excellent agreement (2%) with the absolute value of k (CH 3 + HBr) at 300 K derived from ref and ref . Reference 41 is a relative measurement of k (CH 3 + HBr) with k (CH 3 + HI) combined with data of ref for the latter.…”

Section: Metatheses Of R• With Hx and X2supporting

confidence: 82%

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Benson

Dobis

1998

J. Phys. Chem. A

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A large number of reactions of the type R• + HX and R• + X2 have been reported as having negative activation energies (X = I, Br, Cl). These reactions have none of the behavior of reactions that are expected to have negative activation energies. It is shown that they must be simple metathesis reactions having a single transition state, (R·H·Ẋ)⧧ or (R·X·Ẋ)⧧. It is concluded that the negative activation energies must be artifacts of the experimental techniques employed. Some of what appear to be simple metathesis reactions but which proceed via atom + radical recombination have had rate constants reported, close to the collision limit. When examined from a collisional point of view, it is shown that they require collision diameters from 8 to 25 Å, far in excess of any known long-range interaction at these distances between neutral species. Again, artifacts of the experimental methods may be responsible.

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Section: Metatheses Of R• With Hx and X2supporting

confidence: 82%

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Benson

Dobis

1998

J. Phys. Chem. A

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“…The reactions of small alkyl radicals (such as CH 3 , C 2 H 5 , i ‐C 3 H 7 , and t ‐C 4 H 9 ) with HBr have been extensively studied during the past decades 1–14. Beyond their importance for the fundamental chemical kinetics, these kinetic measurements have been a major source of information on the CH bond energies and the heats of formation of small alkyl radicals 5, 6.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study on the rate constants for the C₂H₅ + HBr → C₂H₆ + Br reaction

Sheng

Liu

et al. 2003

J Comput Chem

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The reaction C(2)H(5) + HBr --> C(2)H(6) + Br has been theoretically studied over the temperature range from 200 to 1400 K. The electronic structure information is calculated at the BHLYP/6-311+G(d,p) and QCISD/6-31+G(d) levels. With the aid of intrinsic reaction coordinate theory, the minimum energy paths (MEPs) are obtained at the both levels, and the energies along the MEP are further refined by performing the single-point calculations at the PMP4(SDTQ)/6-311+G(3df,2p)//BHLYP and QCISD(T)/6-311++G(2df,2pd)//QCISD levels. The calculated ICVT/SCT rate constants are in good agreement with available experimental values, and the calculate results further indicate that the C(2)H(5) + HBr reaction has negative temperature dependence at T < 850 K, but clearly shows positive temperature dependence at T > 850 K. The current work predicts that the kinetic isotope effect for the title reaction is inverse in the temperature range from 200 to 482 K, i.e., k(HBr)/k(DBr) < 1.

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Not only they are important for the fundamental chemical kinetics, but also the measured rate constants provide a major source for determination the heats of formation of the radicals and the C-H bond energies. 5,6 The most early measured results revealed that these reactions of small hydrocarbon free radicals ͑such as CH 3 , C 2 H 5 , i-C 3 H 7 , t-C 4 H 9 ) with HBr were activated processes characterized by small positive activation energy.…”

Section: Introductionmentioning

confidence: 99%

“…5,6 The most early measured results revealed that these reactions of small hydrocarbon free radicals ͑such as CH 3 , C 2 H 5 , i-C 3 H 7 , t-C 4 H 9 ) with HBr were activated processes characterized by small positive activation energy. [1][2][3][4] However, since 1988, a number of experimental kinetic studies 5,7-10 using flash photolysis techniques have found out the negative activation energy and high rate constants for these reactions. On the other hand, the results of these studies were also severely criticized by Benson et al [11][12][13] and Golden et al 14 They applied the very low pressure reactor ͑VLPR͒ technique to study these reactions, and strongly suggested that the reactions of small alkyl radicals with HBr have the small positive activation energy and lower rate constants.…”

Section: Introductionmentioning

confidence: 99%

Computational study of the rate constants and kinetic isotope effects for the CH3+HBr→CH4+Br reaction

Sheng

Liu

et al. 2003

The Journal of Chemical Physics

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The reactions CH n D 4−n + OH → P and CH 4 + OD → CH 3 + HOD as a test of current direct dynamics computational methods to determine variational transition-state rate constants. I. Potential energy surface for a seven-atom reaction. Thermal rate constants and kinetic isotope effects for CH 4 +OH Ab initio direct dynamics methods have been used to study the title reaction. The electronic structure information including geometries, gradients and force constants ͑Hessians͒ is calculated at the QCISD/6-31ϩG(d) level. With the aid of intrinsic reaction coordinate theory, the minimum energy path ͑MEP͒ is obtained at the same level, and the energies along the MEP are further refined by performing the single-point calculations at the PMP4/6-311ϩϩG(3d f ,3pd) level. For this reaction, the theoretical rate constants by using improved canonical variational transition state theory incorporating small-curvature tunneling correction are in excellent agreement with the more recent experimental values. Our calculated results show that for the CH 3 ϩHBr reaction, the rate constants have a strong nonlinear Arrhenius behavior, i.e., the CH 3 ϩHBr reaction has negative temperature dependence at TϽ536 K, but clearly shows positive temperature dependence at T Ͼ536 K. The current work predicts that the kinetic isotope effect for the title reaction is normal in the temperature range 200-482 K, i.e., k HBr /k DBr Ͼ1. This result is in good agreement with the experimental one.

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Effect of deuterium iodide and hydrogen bromide on the photo-oxidation of methyl iodide

Cited by 11 publications

References 0 publications

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Theoretical study on the rate constants for the C₂H₅ + HBr → C₂H₆ + Br reaction

Computational study of the rate constants and kinetic isotope effects for the CH3+HBr→CH4+Br reaction

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Effect of deuterium iodide and hydrogen bromide on the photo-oxidation of methyl iodide

Cited by 11 publications

References 0 publications

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Theoretical study on the rate constants for the C2H5 + HBr → C2H6 + Br reaction

Computational study of the rate constants and kinetic isotope effects for the CH3+HBr→CH4+Br reaction

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Theoretical study on the rate constants for the C₂H₅ + HBr → C₂H₆ + Br reaction