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Type‐I Dyotropic Reactions: Understanding Trends in Barriers
Author(s) -
Fernández Israel,
Bickelhaupt F. Matthias,
Cossío Fernando P.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200897
Subject(s) - reactivity (psychology) , chemistry , valence (chemistry) , density functional theory , transition state theory , transition state , valence bond theory , computational chemistry , crystallography , molecule , reaction rate constant , physics , kinetics , catalysis , molecular orbital , organic chemistry , quantum mechanics , medicine , alternative medicine , pathology
To understand the factors that control the activation barrier of type‐I 1,2‐dyotropic reactions (X‐EH 2 ‐CH 2 ‐X*→X*‐EH 2 ‐CH 2 ‐X, with E=C and Si, X=H, CH 3 , SiH 3 , 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 CH 2 CH 2 and [X⋅⋅⋅X] fragments in X‐CH 2 ‐CH 2 ‐X. The picture that emerges from these analyses is that reduced CX 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 CX 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.