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The Mechanism of Hydrolysis of Aryldiazonium Ions Revisited: Marcus Theory vs. Canonical Variational Transition State Theory.

Authors :
García Martínez, Antonio
de la Moya Cerero, Santiago
Osío Barcina, José
Moreno Jiménez, Florencio
Lora Maroto, Beatriz
Source :
European Journal of Organic Chemistry. Dec2013, Vol. 2013 Issue 27, p6098-6107. 10p.
Publication Year :
2013

Abstract

Several models, theoretical levels and computational methods, all based on the canonical variational transition state approximation, have been used to predict both the experimental activation energies (Δ Eexp≠) and the experimental activation free energies (Δ Gexp≠) for the hydrolysis of aryldiazonium ions. It is demonstrated that the computation of activation energies (Δ E≠), instead of activation free energies (Δ G≠), agrees better with the corresponding experimental data, showing that the employed computational methods do not afford reliable entropic contributions to the free energy barriers in the case of the studied reaction. However, the most fitted computations of Δ E≠ were not able to clearly differentiate between the mechanisms proposed for this interesting reaction (SN1, SN2 and water cluster). In contrast, the use of the Marcus theory (hyperbolic-cosine equation) instead of the canonical variational transition state theory leads to excellent agreement between the in-water-computed activation energies (Δ EwM≠) and the corresponding Δ Eexp≠ values for the SN2 mechanism, but far beyond the limit of error for the SN1 process. The validity of the Marcus theory for the studied SN1 and SN2 reactions is ensured by the fact that both reactions can be described as SET processes. On the other hand, apparently compelling evidence against the SN2 mechanism, such as 13C KIEs and experimental observation of N2 scrambling, are also discussed and alternative explanations are proposed. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
1434193X
Volume :
2013
Issue :
27
Database :
Academic Search Index
Journal :
European Journal of Organic Chemistry
Publication Type :
Academic Journal
Accession number :
90180487
Full Text :
https://doi.org/10.1002/ejoc.201300834