Cross‐reaction and cross‐combination ratios

Arthur, N. L.; Christie, John

doi:10.1002/kin.550190309

Cited by 15 publications

(11 citation statements)

References 17 publications

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“…36 For the cross-reaction (4) this relation applies only in case of MeOBp. For the other derivatives k4 is subsequently larger than twice the geometric mean of k3 and k6, and the deviation increases with increasing electron withdrawing strength of the ring substituents.…”

Section: The Ketyl Radical -Ketyl Radical Reactionsmentioning

confidence: 99%

Substituent Effect on the Photoreduction Kinetics of Benzophenone

et al. 2013

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The kinetics of the photoreduction of four benzophenone derivatives by isopropyl alcohol was examined in acetonitrile, namely tetra-meta-trifluoromethyl-, di-para-trifluoromethyl-, di-paramethoxy benzophenone and for comparison the unsubstituted molecule itself. The basic spectroscopic (absorption and phosphorescence spectra) and photophysical (quantum yields, excited state energies) properties were established, and the key kinetic parameters were determined by the laser flash photolysis transient absorption technique. The rate coefficients of both the primary and secondary photoreduction reaction show remarkable dependence on ring substitution. This substantial effect is caused by the considerable change in the activation energy of the corresponding process. The experimental results as well as DFT quantum chemical calculations clearly indicate that these benzophenone derivatives all react as n-π* excited ketones, and the rate as well as the activation energy of the reduction steps change parallel with the reaction enthalpies, the determining factor being the stability of the forming aromatic ketyl 2 radicals. The secondary photoreduction of benzophenones by the aliphatic ketyl radical formed in the primary step occurs via a hydrogen bonded complex. The binding energy of the hydrogen bonded complex between the aliphatic ketyl radical reactant and a solvent molecule is a critical parameter influencing the observable rate of the secondary photoreduction.

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Section: The Ketyl Radical -Ketyl Radical Reactionsmentioning

confidence: 99%

Substituent Effect on the Photoreduction Kinetics of Benzophenone

et al. 2013

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“…Both the plots were very similar. The datum points at room temperature indicate a n additional source of C3F7H formation, i.e., reaction (12). This may be true, to a much lesser extent, at 79"C, and we did not weight these datum points in the best straight lines.…”

Section: R(csmentioning

confidence: 95%

“…As we shall see reaction (6) is considerably slower than reaction (13), and makes little contribution to the C3F7H product yields at 22°C. The slope of the line at 22°C in Figure 2 is determined largely by reaction (12) and at 79°C its occurrence may still be significant enough to contribute to the C3F7H yields.…”

Section: Mass Balance and The Propionyl Radicalmentioning

confidence: 99%

Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro‐n‐propyl and ethyl radicals revisited

Pritchard

Abbas

Kennedy

et al. 1990

Int J of Chemical Kinetics

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A redetermination of the disproportionation/combination ratio for n-CsF7 and CzH5 radicals gives a value of A(n-C3F7, CtH,) = 0.13 t 0.01, independent of the temperature. The radicals were produced by the photolysis of n-C3F&OC2Hs. The previous determinations of this ratio are discussed and are found to be largely incorrect. The values for A(CF3, CzH5) and A(CzF5, C2H5) are also re-evaluated, and the recommended values are 0.10 2 0.02 and 0.12 t 0.02, respectively. Systems involving perfluoroalkyl and ethyl radicals are complicated due to rapid perfluororadical addition to the ethylene formed in the disproportionation process. The extent of this reaction, and its consequences, are discussed and evaluated. The role of the propionyl (C2H5CO) radical in the room temperature photolysis is also assessed. However, it is found that the A values determined by the intercept method used in this work are not affected by the secondary reactions that occur. It is concluded that high cross-combination ratios are general to perfluoroalkyl-alkyl radical interactions. For C3F7 and CzHs radicals the ratio is 2.7-2.8. Above 100°C ratios exceed 3 due to secondary reactions.

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“…As each of the steps (1)- (3) corresponds to a recombination reaction, characterized by a weak temperature dependence, it may be in principle assumed that they obey collision theory for rigid spheres without an activation energy, for which φ ≥ 2 results [16]. Even for such a simple model a value of φ = 2 already represents a singularity, undoubtedly because of fortituous cancellations [16].…”

Section: Introductionmentioning

confidence: 96%

“…Even for such a simple model a value of φ = 2 already represents a singularity, undoubtedly because of fortituous cancellations [16]. In fact, a wide set of examples lead to φ values far lower than 2 (see Table I and Ref.…”

Section: Introductionmentioning

confidence: 98%

Analytical resolution of a parallel second‐order reaction mechanism

Croce

Mogni

Irrazábal

2003

Int J of Chemical Kinetics

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The competition among the three different elementary second-order processes involving the radicals A and B,is frequently established in many combustion and atmospheric chemistry systems. The analytical resolution of the above mechanism for k AB = 2k AA and k AB = 2k BB , that is, for a crosscombination ratio φ = k AB /(k AA k BB ) 1/2 = 2, is well-known, but it has been claimed not to exist for φ = 2. In the present paper an analytical resolution of the system (1)- (3), performed under the condition k AB = 2k AA and k AB = 2k BB , leads toThe mathematical procedure leading to this equation and the equation itself are valid independently of the nature of the products of the reactions (1), (2), and (3), that is, recombination or disproportionation products, provided that the reactants and the order of the reactions remain the same.

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Cross‐reaction and cross‐combination ratios

Cited by 15 publications

References 17 publications

Substituent Effect on the Photoreduction Kinetics of Benzophenone

Substituent Effect on the Photoreduction Kinetics of Benzophenone

Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro‐n‐propyl and ethyl radicals revisited

Analytical resolution of a parallel second‐order reaction mechanism

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