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Hydrogen‐Abstraction Reactivity Patterns from A to Y: The Valence Bond Way
Author(s) -
Lai Wenzhen,
Li Chunsen,
Chen Hui,
Shaik Sason
Publication year - 2012
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201108398
Subject(s) - valence bond theory , hydrogen atom abstraction , chemistry , abstraction , reactivity (psychology) , valence (chemistry) , electron transfer , hydrogen atom , computational chemistry , molecule , hydrogen , photochemistry , molecular orbital , organic chemistry , philosophy , alkyl , alternative medicine , epistemology , pathology , medicine
“Give us insight, not numbers” was Coulson’s admonition to theoretical chemists. This Review shows that the valence bond (VB)‐model provides insights and some good numbers for one of the fundamental reactions in nature, the hydrogen‐atom transfer (HAT). The VB model is applied to over 50 reactions from the simplest H + H 2 process, to P450 hydroxylations and H‐transfers among closed‐shell molecules; for each system the barriers are estimated from raw data. The model creates a bridge to the Marcus equation and shows that H‐atom abstraction by a closed‐shell molecule requires a higher barrier owing to the additional promotion energy needed to prepare the abstractor for H‐abstraction. Under certain conditions, a closed‐shell abstractor can bypass this penalty through a proton‐coupled electron transfer (PCET) mechanism. The VB model links the HAT and PCET mechanisms conceptually and shows the consequences that this linking has for H‐abstraction reactivity.