Hydrogen-Abstraction Reactivity Patterns from A to Y: The Valence Bond Way

Authors

  • Dr. Wenzhen Lai,

    1. Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
    2. Department of Chemistry, Renmin University of China, Beijing, 100872 (China)
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    • These authors contributed equally to this work.

  • Dr. Chunsen Li,

    1. Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
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    • These authors contributed equally to this work.

  • Prof. Dr. Hui Chen,

    1. Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
    2. Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 (China)
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  • Prof. Dr. Sason Shaik

    Corresponding author
    1. Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
    • Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel)
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Abstract

“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 + H2 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.

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