Kinetics and mechanism for the H‐for‐X exchange process in the H + C<sub>6</sub>H<sub>5</sub>X reactions: A computational study

Tokmakov, I. V.; Lin, Ming‐Chang

doi:10.1002/kin.1062

Cited by 16 publications

(31 citation statements)

References 56 publications

(78 reference statements)

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“…This is in order-of magnitude accord with our measurements: the DFT data overestimate the combined addition path by about a factor of 2 at 300 K and a factor of 5 at 600 K. By analogy with H + C6H6, the addition channels (7b-7d) will be at their high-pressure limits under our experimental conditions. We note that the significant barrier of ~111 kJ mol -1 relative to H + C6H6 for 1,2 H-shifts in cyclohexadienyl [22] means that these channels are distinct.…”

Section: Resultsmentioning

confidence: 82%

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Gao

Marshall

2009

Proceedings of the Combustion Institute

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Section: Resultsmentioning

confidence: 82%

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Gao

Marshall

2009

Proceedings of the Combustion Institute

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“…It is clear from the very large number of computations already carried out on the gas phase anionic S N 2 reactions that the energy profiles are very sensitive to the level of theory employed. For this reason, here we use a higher level of theory, specifically a modification of the Gaussian‐2 (G2M) theory introduced by Mebel and coworkers,8 which is more accurate than G2 for atomization energies, and has been extensively used in the study of reaction mechanisms,9–12 and hope to obtain more reliable estimation of the energy profile for the ion‐pair S N 2 reactions.…”

Section: Methodsmentioning

confidence: 99%

Modified Gaussian‐2 level investigation of the identity ion‐pair S_N2 reactions of lithium halide and methyl halide with inversion and retention mechanisms

Ren

Chu

2004

J Comput Chem

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Identity ion-pair S(N)2 reactions LiX + CH(3)X --> XCH(3) + LiX (X = F, Cl, Br, and I) have been investigated in the gas phase and in solution at the level of the modified Gaussian-2 theory. Two possible reaction mechanisms, inversion and retention, are discussed. The reaction barriers relative to the complexes for the inversion mechanism [DeltaH(cent) ( not equal )(inv)] are found to be much higher than the corresponding values for the gas phase anionic S(N)2 reactions, decreasing in the following order: F (263.6 kJ mol(-1)) > Cl (203.3 kJ mol(-1)) > Br (174.7 kJ mol(-1)) > I (150.7 kJ mol(-1)). The barrier gaps between the two mechanisms [DeltaH(cent) ( not equal ) (ret) - DeltaH(cent) ( not equal ) (inv)] increase in the order F (-62.7 kJ mol(-1)) < Cl (4.4 kJ mol(-1)) < Br (24.9 kJ mol(-1)) < I (45.1 kJ mol(-1)). Thus, the retention mechanism is energetically favorable for fluorine and the inversion mechanism is favored for other halogens, in contrast to the anionic S(N)2 reactions at carbon where the inversion reaction channel is much more favorable for all of the halogens. The stabilization energies for the dipole-dipole complexes CH(3)X. LiX (DeltaH(comp)) are found to be similar for the entire set of systems with X = F, Cl, Br, and I, ranging from 53.4 kJ mol(-1) for I up to 58.9 kJ mol(-1) for F. The polarizable continuum model (PCM) has been used to evaluate the direct solvent effects on the energetics of the anionic and ion-pair S(N)2 reactions. The energetic profiles are found to be still double-well shaped for most of the ion-pair S(N)2 reactions in the solution, but the potential profile for reaction LiI + CH(3)I is predicted to be unimodal in the protic solvent. Good correlations between central barriers [DeltaH(cent) ( not equal ) (inv)] with the geometric looseness of the inversion transition state %C-X( not equal ), the dissociation energies of the C-X bond (D(C-X)) and Li-X bond (D(Li-X)) are observed, respectively.

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“…Uc et al have calculated the relative stability, ΔHr (298 K), of all four methyl-CHD isomers relative to toluene + H. 31 Tokmakov and Lin calculated the reaction profile for H + toluene → ipso-methyl-CHD and thence to benzene + CH3. 32 They also calculated the barrier to the [1,2]-H shift between ipso and ortho isomers to be vastly in excess of the C-H bond energy. To our knowledge, the electronic spectroscopy of methyl-CHD has not been reported.…”

Section: Previous Work On Chd Hydroxy-chd and Methyl-chdmentioning

confidence: 99%

Hydrogen-atom attack on phenol and toluene is ortho-directed

Krechkivska

Wilcox

Troy

et al. 2016

Phys. Chem. Chem. Phys.

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The reaction of H + phenol and H/D + toluene has been studied in a supersonic expansion after electric discharge. The (1 + 1') resonance-enhanced multiphoton ionization (REMPI) spectra of the reaction products, at m/z = parent + 1, or parent + 2 amu, were measured by scanning the first (resonance) laser. The resulting spectra are highly structured. Ionization energies were measured by scanning the second (ionization) laser, while the first laser was tuned to a specific transition. Theoretical calculations, benchmarked to the well-studied H + benzene → cyclohexadienyl radical reaction, were performed. The spectrum arising from the reaction of H + phenol is attributed solely to the ortho-hydroxy-cyclohexadienyl radical, which was found in two conformers (syn and anti). Similarly, the reaction of H/D + toluene formed solely the ortho isomer. The preference for the ortho isomer at 100-200 K in the molecular beam is attributed to kinetic, not thermodynamic effects, caused by an entrance channel barrier that is ∼5 kJ mol(-1) lower for ortho than for other isomers. Based on these results, we predict that the reaction of H + phenol and H + toluene should still favour the ortho isomer under elevated temperature conditions in the early stages of combustion (200-400 °C).

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Kinetics and mechanism for the H‐for‐X exchange process in the H + C₆H₅X reactions: A computational study

Cited by 16 publications

References 56 publications

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Modified Gaussian‐2 level investigation of the identity ion‐pair S_N2 reactions of lithium halide and methyl halide with inversion and retention mechanisms

Hydrogen-atom attack on phenol and toluene is ortho-directed

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Kinetics and mechanism for the H‐for‐X exchange process in the H + C6H5X reactions: A computational study

Cited by 16 publications

References 56 publications

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Modified Gaussian‐2 level investigation of the identity ion‐pair SN2 reactions of lithium halide and methyl halide with inversion and retention mechanisms

Hydrogen-atom attack on phenol and toluene is ortho-directed

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Kinetics and mechanism for the H‐for‐X exchange process in the H + C₆H₅X reactions: A computational study

Modified Gaussian‐2 level investigation of the identity ion‐pair S_N2 reactions of lithium halide and methyl halide with inversion and retention mechanisms