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Anomalous kinetic hydrogen isotope effect in the oxidation of formate by bromine: Tunneling via an intermediate

Brusa, M. A. and Colussi, A. J. (1982) Anomalous kinetic hydrogen isotope effect in the oxidation of formate by bromine: Tunneling via an intermediate. International Journal of Chemical Kinetics, 14 (11). pp. 1211-1218. ISSN 0538-8066. http://resolver.caltech.edu/CaltechAUTHORS:20150803-152424653

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Abstract

Rates of oxidation of XCOO^− (X = H, D) by Br_2 in acid aqueous media were measured between 274 and 332 K. The derived Arrhenius parameters for both reactions log k_H(M^(-1) s^(-1) = (18.81 ± 0.10) - (14.33 ± 0.13)/ø log k_D(M^(-1) s^(-1) = (13.77 ± 0.13) - (17.62 ± 0.04)/ø where θ = 4.575T × 10^(−3) kcal/mol, with (k_H/k_D)_(298K) = 2.85, reveal a primary isotope effect, but the difference (E_D - E_H) = 3.29 kcal/mol and the ratio A_D/A_H = 91 fall beyond the limits imposed by semiclassical transition-state theory, suggesting tunneling or a multiple-stage mechanism. However, it can be shown that either tunneling in a single step or a three-step, internal return mechanism can be ruled out as alternative models, since both require unreasonable kinetic parameters to fit the data. The simplest scheme accounting for the present observations involves tunneling in the decomposition of a charge transfer complex in equilibrium with the reactants.


Item Type:Article
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http://dx.doi.org/10.1002/kin.550141105DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/kin.550141105/abstractPublisherArticle
ORCID:
AuthorORCID
Colussi, A. J.0000-0002-3400-4101
Additional Information:© 1982 John Wiley & Sons. Received December 8, 1981, Accepted June 4, 1982. This work was supported by the Comisión de Investigaciones Científicas de Ia Provincia de Buenos Aires.
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Comisión de Investigaciones Científicas de Ia Provincia de Buenos AiresUNSPECIFIED
Record Number:CaltechAUTHORS:20150803-152424653
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150803-152424653
Official Citation:Brusa, M. A. and Colussi, A. J. (1982), Anomalous kinetic hydrogen isotope effect in the oxidation of formate by bromine: Tunneling via an intermediate. Int. J. Chem. Kinet., 14: 1211–1218. doi: 10.1002/kin.550141105
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59156
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:05 Aug 2015 22:19
Last Modified:05 Aug 2015 22:19

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