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Article Dans Une Revue Journal of the American Chemical Society Année : 1997

Linear Free Energy of Activation Relationship for Barrierless Association Reactions

Résumé

An analysis of variational transition state theory rate constants, for the association reactions Cl- + CH3Cl, Cl- + CH3Br, H + CH3, H + diamond{111}, CH3 + CH3, and Al + Al2 shows that the free energy of activation ΔG varies nearly linearly with temperature, over a broad temperature range, for each reaction. This suggests that association rate constants can be parametrized by the free energy of activation at 300 K, Δ , and the change in ΔG with temperature, ΔΔG/ΔT. The near linear dependence of ΔG with temperature is supported by a semiempirical model for association kinetics. The rate constants for Cl- + CH3Cl, Cl- + CH3Br, and CH3 + CH3 decrease with increase in temperature, while those for H + CH3, H + diamond{111}, and Al + Al2 slightly increase. For the six association reactions considered here, the linear free energy relationship gives semiquantitative rate constants over a rather broad temperature range of 200−2000 K. To calculate accurate rate constants over a broader temperature range, particularly at low temperatures, nonlinear terms must be included in the free energy expansion.

Dates et versions

hal-00737334 , version 1 (01-10-2012)

Identifiants

Citer

Pascal de Sainte Claire, William L. Hase, Gilles H. Peslherbe, H. Wang. Linear Free Energy of Activation Relationship for Barrierless Association Reactions. Journal of the American Chemical Society, 1997, 119, pp.5007-5012. ⟨10.1021/ja961239b⟩. ⟨hal-00737334⟩
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