Non-conservation of activation energy barriers in the same chemical process: a cooperative (effect) proton transfer on (
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Non‑conservation of activation energy barriers in the same chemical process: a cooperative (effect) proton transfer on (HF)n molecular aggregates Sara. F. de A. Morais1,2,3 · Kleber C. Mundim2 · Daví A. C. Ferreira1 Received: 12 March 2020 / Accepted: 5 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The formation of (HF)n aggregates with n = 2, 3, 4, 5 and 6 and concerted proton transfer processes in these aggregates were systematically analyzed. It was verified that, by a cooperative effect, the barrier associated with the proton transfer process decreases for aggregates with a larger number of molecules, indicating that the activation energy for proton transfer depends on the molecularity of the process. Natural bond orbital and quantum theory of atoms in molecules were used to characterize the strength of the hydrogen bonds established in the aggregates, which verified a general increase in the delocalization energy as a function of increasing aggregate size. A deformed Eyring (d-Eyring) equation was used to calculate the proton transfer rate constants, where the d-Eyring equation adequately described the proton transfer kinetics. Analysis of the rate constants showed that proton transfer became faster as the cluster size increased. Arrhenius and d-Arrhenius plots showed a decrease in the dependence of the rate constants on temperature, particularly for the tetramer, pentamer, and hexamer. The d-Arrhenius plots, for which the d parameter was included in the Eyring equation, suggest non-Arrhenius behavior for proton transfer in the HF aggregates at low temperatures. Keywords Cooperative effects · HF aggregates · Hydrogen bonds · Proton transfer rates
"Festschrift in honor of Prof. Fernando R. Ornellas" Guest Edited by Adélia Justino Aguiar Aquino, Antonio Gustavo Sampaio de Oliveira Filho and Francisco Bolivar Correto Machado. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02681-1) contains supplementary material, which is available to authorized users. * Sara. F. de A. Morais [email protected]; [email protected] * Daví A. C. Ferreira [email protected] 1
Laboratório de Dinâmica e Reatividade Molecular, Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, CP 04478, Asa Norte ‑ Brasília, DF CEP: 70904‑970, Brazil
2
Laboratório de Modelagem de Sistemas Complexos, Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, CP 04478, Asa Norte ‑ Brasília, DF CEP: 70904‑970, Brazil
3
Grupo de Química Computacional Aplicada, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, São Paulo 05508‑000, Brazil
1 Introduction For several decades, the formation of hydrogen halide aggregates has been explored, driven by the interest in the varied architectures and the nature of the interactions in these aggregates, as well as the resulting properties manifested by molecular cooperativity [1–6]. Among the intera
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