Chemiluminescent recombination of formyl radicals

Hartley, David

doi:10.1039/c19670001281

Cited by 6 publications

(5 citation statements)

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“…At the UHF level, OCCHO is at least 100 kJ mol -1 more stable than 15 other competing structural isomers. However, the radical is not readily formed from the parent C 2 H 2 O 2 , glyoxal, because the glyoxal C−C bond, rather than the C−H bond, tends to cleave during photolysis and combustion. , Hartley established a C−C bond strength of 299 kJ mol -1 for glyoxal, significantly lower than the typical aldehyde C−H bond strength of 365 kJ mol -1 . Previous calculations have been carried out by Langenberg and Ruttink on the isoelectronic C 2 H 2 radical cation.…”

Section: Resultsmentioning

confidence: 99%

Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Cooksy

2001

J. Am. Chem. Soc.

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A survey of the XCNY and XCCHY radicals with X and Y = CH(2), NH, and O has been carried out by ab initio QCISD/6-311G(d,p) calculations to assess the impact of low-lying excited electronic states on the molecular dynamics. Multiple canonical structures may be drawn for each of these structural formulas, with the principal competition for most stable configuration between a (2)A' form with four electrons in a" orbitals and a (2)A" form with five a" electrons. Other low-lying configurations may include a 5a" state with nominally pentavalent nitrogen and a 6a" state. Optimized geometries and harmonic frequencies were evaluated for the lowest-energy minima on the potential energy surfaces. Localized unpaired electron density causes the 4a" state to be the most stable for (NH)CCHO and OCCHY, whereas allylic resonance stabilization favors the 5a" state for all other radicals in the set. For five of the 18 molecules studied, secondary minima (excluding conformers) are found within 30 kJ mol(-)(1) of the most stable state at the QCISD/6-311G(d,p) level, suggesting that photolysis or pyrolysis of parent compounds may result in multiple isomers of the resulting reactive intermediates. Predicted equilibrium geometries, approximate thermochemical quantities for dissociation of the central bond, and selected spectroscopic parameters are presented for all 18 structural formulas. Convergence tests were also performed for the glyoxallyl radical (OCCHO) to resolve discrepancies between single- and multireference post-SCF results. These tests find that extension of the MCSCF methods to include sigma bonding orbitals or virtual-orbital CI brings MCSCF relative energies into agreement with results from standard single-reference CI and CC methods. Relative configurational energies evaluated at Hartree-Fock levels routinely differ from post-SCF values by 30 kJ mol(-1) or more.

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Section: Resultsmentioning

confidence: 99%

Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Cooksy

2001

J. Am. Chem. Soc.

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“…Conditions of low optical densities and low excitation (D_ « 1) lead by expansion of Beer's law to eq 12. V_/V_ is formed in an 1 VD ~= In 10 V. (12) analogue voltage divider, and D_ is analyzed by a superheterodyne lock-in amplifier. As will be shown elsewhere, 31 starting material and products contribute to the signal only at very low modulation frequencies (o>/(2ir) 5 5 s'1) under our conditions.…”

Section: Resultsmentioning

confidence: 99%

“…Insertion into eq 27 with tr » rP shows that deviations from eq 28 are expected even for being small, not exceeding a few percent. Figures [10][11][12] give the experimental kinetics determined from the out-of-phase components of the phosphorescence as those of Figure 8. Obviously, the linear dependence is obeyed for all temperatures.…”

Section: Resultsmentioning

confidence: 99%

Self-termination of benzoyl radicals to ground- and excited-state benzil. Symmetry control of a radical combination

Huggenberger¹,

Lipscher²,

Fischer³

1980

J. Phys. Chem.

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“…It seems probable that the low value results from an incorrect assignment of the adiabatic ionization potential. The fifth method 36 involves observation of chemiluminescence from glyoxal, (CHO) 2 , formed via CHO radical recombination, giving D 298 (OHC-CHO) ) 299.2 ( 1.3 kJ mol -1 . This was used by Fletcher and Pilcher 29 to obtain D 298 (H-CHO) ) 370.3 ( 3.8 kJ mol -1 , corresponding to ∆H f °(CHO) ) 43.7 ( 3.8 kJ mol -1 .…”

Section: B Thermochemistry Of Cho and The Related Bond Dissociation E...mentioning

confidence: 99%

Time-Resolved Studies of the Kinetics of the Reactions of CHO with HI and HBr: Thermochemistry of the CHO Radical and the C−H Bond Strengths in CH₂O and CHO

1997

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Time-resolved studies of formyl radical, CHO, generated by laser flash photolysis of acetaldehyde, have been carried out to obtain rate constants for its bimolecular reactions with HI and HBr. Each reaction was studied in the gas-phase at five different temperatures in the range 293-540 K. The pressure-independent rate constants gave the following Arrhenius equations: for CHO + HI, log(k 2 /cm 3 molecule -1 s -1 ) ) (-11.51 ( 0.01) -(0.83 ( 0.06 kJ mol -1 )/ RT ln 10, for CHO + HBr, log(k 4 /cm 3 molecule -1 s -1 ) ) (-12.59 ( 0.06) -(0.13 ( 0.44 kJ mol -1 )/ RT ln 10. The Arrhenius parameters are consistent with those for reactions of other free radicals with HI and HBr and support the idea of intermediate complexes in these processes. Combination with the known kinetic data on the reverse reactions leads to the thermodynamic estimate for ∆H f °(CHO) ) 44.29 ( 0.43 kJ mol -1 (third law method, 298 K value). Second law values are in reasonable agreement. This value corresponds to the bond dissociation energies D(H-CHO) ) 370.86 ( 0.28 kJ mol -1 , and D(H-CO) ) 63.18 ( 0.46 kJ mol -1 . These values are in close agreement with several previous determinations although more precise. A small unresolved discrepancy exists with the most recent value for the photodissociation threshold for CH 2 O.

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Chemiluminescent recombination of formyl radicals

Cited by 6 publications

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Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Self-termination of benzoyl radicals to ground- and excited-state benzil. Symmetry control of a radical combination

Time-Resolved Studies of the Kinetics of the Reactions of CHO with HI and HBr: Thermochemistry of the CHO Radical and the C−H Bond Strengths in CH₂O and CHO

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Chemiluminescent recombination of formyl radicals

Cited by 6 publications

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Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Relocalization in Floppy Free Radicals: The OCNO and OCCHO Isoelectronic Series

Self-termination of benzoyl radicals to ground- and excited-state benzil. Symmetry control of a radical combination

Time-Resolved Studies of the Kinetics of the Reactions of CHO with HI and HBr: Thermochemistry of the CHO Radical and the C−H Bond Strengths in CH2O and CHO

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Time-Resolved Studies of the Kinetics of the Reactions of CHO with HI and HBr: Thermochemistry of the CHO Radical and the C−H Bond Strengths in CH₂O and CHO