Insertion of methylene into alkanes

Halberstadt, Marcel L.; McNesby, J. R.

doi:10.1021/ja00990a008

Cited by 54 publications

(12 citation statements)

References 24 publications

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“…Semi-empirical corrections to the latter are required to achieve 9 kcal/mole ll . Thus now it again appears that theory and experiment are in good accord, though a possible discrepancy of [1][2][3] kcal/mole remains with ab initio calculations .…”

Section: Introductionmentioning

confidence: 83%

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Quantum Monte Carlo calculation of the singlet–triplet splitting in methylene

Reynolds

Dupuis

Lester

1985

The Journal of Chemical Physics

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The fixed-node quantum Monte Carlo (QMC) method is used to calculate the total energy of CH 2 in the ~1 and 1A1 states. For both states. the best QMC variationally bounded energies lie more than 15 kcal/mole (0.024 h) below the best previous variational calculations. Subtracting these energies to obtain the singlet-triplet splitting yields Ta = 9.4 ± 2.2 kcal/mole. Adjusting for zero-point energies and relativistic effects. we obtain To =8.9±2.2 kcal/mole. This result is in excellent agreement with the recent direct measurements of McKellar et. ai.of To =9.05±0.06 kcal/mole. and of Leopold et. ai. of "'9 kcal/mole. as well as with recent theoretical investigations which indicate an energy gap of 9-11 kCal/mole. We summarize the QMC method. discuss a possible scheme for iteratively correcting the procedure. and note that the present results were obtained using only single determinant functions for both states. in contrast to conventional ab initio approaches which must use at'least two configurations to properly describe the singlet state. '• A preliminary account of this work was presented at the 17th Annual Sanibel SympOSium, March 1983.

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Section: Introductionmentioning

confidence: 83%

“…Theory2 predicted a splitting of 30 kcal/mole, while experiment 3 . ultimately has come to favor values in the range of 9-11 kcal/mole 11, with ab initio values in the 10-11 kcal/mole range 4 .…”

Section: Introductionmentioning

confidence: 99%

Quantum Monte Carlo calculation of the singlet–triplet splitting in methylene

Reynolds

Dupuis

Lester

1985

The Journal of Chemical Physics

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“…The Rice-Ramsperger-Kassel-Marcus (RRKM) [4,17- eigenstates for the activated complex up to the energy E+, and [20,2 11. The sums of the vibrational-internal rotational states for the activated complexes and the densities of the vibrationalinternal rotational states for the molecules were calculated using the approximation developed by Whitten and Rabinovitch [22].…”

Section: A Rrkm and Absolute Rate Theorymentioning

confidence: 99%

“…The decomposition of vibrationally excited ethane, formed by the insertion of singlet methylenes into the C-H bonds of methane, has been studied by Bell and Kistiakowsky [ 11 and more recently by Halberstadt and McNesby [2]. Whitten and Rabinovitch [3] measured the decomposition rates of Chemically activated isobutane and n-butane formed by the reaction of methylene with propane.…”

Section: Introductionmentioning

confidence: 99%

The decomposition of chemically activated n–butane, isopentane, neohexane, and n–pentane and the correlation of their decomposition rates with radical recombination rates.

Hase

Johnson

Simons

1972

Int J of Chemical Kinetics

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The total decomposition rates of the chemically activated alkanes n-butane, n-pentane, isopentane, and neohexane were measured using an internal comparison technique. Chemical activation was by the C-H insertion reaction of excited singlet-state methylene radicals.A total of ten rate constants ranging from 4.6 X lo5 to 2.3 X lo' sec-' were measured for these alkanes at different excitation energies. These rates correlate via RRKM theory calculations with thermal A-factors in the range of to lo".' sec-' for free rotoractivated complex models and in the range of 1016.4 to sec-' for vibrator-activated complex models. I t was found that high critical energies for decomposition, "tight" radical models, and activated complex models with free internal rotations were required to correlate the decomposition rates of these alkanes with estimated alkyl radical recombination rates. The correlation is just barely possible even for these favorable extremes, indicating that there may be a basic discrepancy between the recombination rate and decomposition rate data for alkanes.

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“…where E = AH + SRT + E E X = 130 kcal, A is the preexponential in column 2, AH is the exothermicity of the insertion (93 kcal/mole), E E X is the energy of singlet CH2 above the triplet ground state (2 kcal) [13], and S is the "effective" number of oscillators taken as 27.…”

Section: Relative Rupture Probability = a [ ( E -E O ) / E ]~-~mentioning

confidence: 99%

Abstraction of hydrogen by methylene

McNesby

Kelly

1971

Int J of Chemical Kinetics

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The photolysis of CD&O at 313 nm in the presence of neopentane was carried out over the temperature range 576-706 K. Analysis of the products and isotopic analysis of the methanes demonstrate abstraction of H from neopentane and D from CD&O by methylene. The relative kinetics of abstraction of H and D have been measured over the temperature range, and the absolute value for the collision yield of the abstraction of H from neopentane by CD2 at 653 K has been been estimated to be about 1.5 X 10" mole-' cm3 sec-l, a value 103 times larger than the corresponding reaction of CH3.

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Insertion of methylene into alkanes

Cited by 54 publications

References 24 publications

Quantum Monte Carlo calculation of the singlet–triplet splitting in methylene

Quantum Monte Carlo calculation of the singlet–triplet splitting in methylene

The decomposition of chemically activated n–butane, isopentane, neohexane, and n–pentane and the correlation of their decomposition rates with radical recombination rates.

Abstraction of hydrogen by methylene

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