Double Group Transfer Reactions: Role of Activation Strain and Aromaticity in Reaction Barriers |
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Authors: | Israel Fernández Dr. F. Matthias Bickelhaupt Prof. Dr. Fernando P. Cossío Prof. Dr. |
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Affiliation: | 1. Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040 Madrid (Spain), Fax: (+34)?913944310;2. Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands), Fax: (+31)?205987629;3. Departamento de Química Orgánica I‐Kimika Organikoa I Saila, Facultad de Química‐Kimika Fakultatea, Universidad del País Vasco‐Euskal Herriko Unibertsitatea and Donostia International Physics Center (DIPC), P.K. 1072, 20080 San Sebastián‐Donostia (Spain), Fax: (+34)?943015270 |
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Abstract: | Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in‐plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high‐energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile ΔE(ζ) and the height of the overall reaction barrier ΔE≠=ΔE(ζ=ζTS) is interpreted in terms of the strain energy ΔEstrain(ζ) associated with deforming the reactants along the reaction coordinate ζ plus the interaction energy ΔEint(ζ) between these deformed reactants: ΔE(ζ)=ΔEstrain(ζ)+ΔEint(ζ). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states. |
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Keywords: | activation strain model aromaticity density functional calculations double group transfer reactions reactivity |
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