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Theoretical relations among rate constants, barriers, and Brønsted slopes of chemical reactions

Marcus, R. A. (1968) Theoretical relations among rate constants, barriers, and Brønsted slopes of chemical reactions. Journal of Physical Chemistry, 72 (3). pp. 891-899. ISSN 0022-3654. doi:10.1021/j100849a019.

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A simple relation, ΔF* = (λ(1 + Δ/λ)^2)/4, derived originally for weak-overlap electron transfers, is explored in a slightly modified version for reactions with considerable resonance splitting, such as atom transfers, proton transfers, and strong-overlap electron transfers. A useful additivity property, λ_(12) = ((λ_(11) + λ_(22))/2, permits barriers ΔF* for cross-reactions to be computed from those of exchange reactions, λ_(ii)/4. Some 45 barriers, calculated from some ten others, agreed with BEBO results, within a few kilocalories per mole. The agreement is analyzed and more general models for which it might occur are considered. A functional relationship between barrier and a degree-of-reaction parameter is devised to avoid commitment to too specific a model. An example where breakdown should occur is also given. Experimental data, as well as quantum mechanical calculations of barriers, will permit further tests. Corollaries of the relation include: (1) a classification of reaction barriers in terms of intrinsic (λ_(ii)) and extrinsic (ΔF^0’) contributions, (2) a rate-constant relation k_(12) ≃ (k_(11)k_(22)K_(12)f_(12))^(1/2) and modifications thereof, (3) a calculation of the local Brønsted slope α from the intercept of the ΔF* vs. ΔF^0' plot, α = (1 + Δ/λ)/2, (4) a relation between k_H/k_D vs. ΔF^0' plots and local α’s, and ( 5 ) other relations among rate constants. Throughout, ΔF* and ΔF^0' refer to an elementary step.

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Marcus, R. A.0000-0001-6547-1469
Additional Information:© 1968 American Chemical Society. (Received August 10, 1967) Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, and to the National Science Foundation for their support of this research.
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American Chemical Society Petroleum Research FundUNSPECIFIED
Issue or Number:3
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Official Citation:Theoretical relations among rate constants, barriers, and Broensted slopes of chemical reactions Rudolph A. Marcus The Journal of Physical Chemistry 1968 72 (3), 891-899 DOI: 10.1021/j100849a019
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59560
Deposited By: George Porter
Deposited On:17 Aug 2015 17:19
Last Modified:10 Nov 2021 22:22

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