Type‐I Dyotropic Reactions: Understanding Trends in Barriers |
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Authors: | Dr Israel Fernández Prof Dr F Matthias Bickelhaupt Prof Dr Fernando P Cossío |
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Institution: | 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, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands);3. Departamento de Química Orgánica I‐Kimika Organikoa I Saila, Facultad de Química‐Kimika Fakultatea, Universidad del País Vasco–Euskal Herriko Unibertsitatea, P. K. 1072, 20080 San Sebastián‐Donostia (Spain) |
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Abstract: | To understand the factors that control the activation barrier of type‐I 1,2‐dyotropic reactions (X‐EH2‐CH2‐X*→X*‐EH2‐CH2‐X, with E=C and Si, X=H, CH3, SiH3, F to I) and trends therein as a function of the migrating groups X, we have explored ten archetypal model reactions of this class using relativistic density functional theory (DFT) at ZORA‐OLYP/TZ2P. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity, which had to be extended from bimolecular to unimolecular reactions. Thus, the above type‐I dyotropic reactions can be conceived as a relative rotation of the CH2CH2 and X???X] fragments in X‐CH2‐CH2‐X. The picture that emerges from these analyses is that reduced C? X bonding in the transition state is the origin of the reaction barrier. Also the trends in reactivity on variation of X can be understood in terms of how sensitive the C? X interaction is towards adopting the transition‐state geometry. A valence bond analysis complements the analyses and confirms the picture emerging from the activation strain model. |
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Keywords: | activation strain model bond theory density functional calculations dyotropic reactions energy decomposition analysis reactivity |
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