Deuterium kinetic isotope effects as redox mechanistic criterions

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This account article focuses on deuterium kinetic isotope effects (KIEs) used as criterions to elucidate redox mechanisms including proton-, hydrogen- and hydride-transfer reactions. Hydrogen atom transfer (HAT) is composed of two elementary steps: electron transfer (ET) and proton transfer (PT), while hydride transfer is composed of three elementary steps: ET, PT, and ET. Large tunneling effects are often observed for proton-coupled electron-transfer (PCET) reactions of metal–oxygen complexes in which ET occurs to the metal center and PT occurs simultaneously to the ligand, exhibiting large KIEs. Whether HAT proceeds via sequential ET/PT, PT/ET, or concerted PCET (cPCET) depending on the redox properties of hydrogen donors and acceptors to exhibit different KIEs. Whether hydride transfer also proceeds via sequential ET/PT/ET, PT/ET/ET, or cPCET/ET depending on the redox properties of hydride donors and acceptors to exhibit different KIEs. Temperature dependence of KIEs for aldehyde deformylation reactions has enabled to distinguish two reaction pathways: one is a HAT and the other is a nucleophilic addition. The change of the mechanism from cPCET to sequential ET/PT is made possible by binding acids to the hydrogen and hydride acceptors when no KIE is observed. Inverse KIEs are also discussed for acid (or deuteron)-promoted ET reactions.

Original languageEnglish
Pages (from-to)1558-1568
Number of pages11
JournalBulletin of the Korean Chemical Society
Issue number12
StatePublished - Dec 2021

Bibliographical note

Publisher Copyright:
© 2021 Korean Chemical Society, Seoul & Wiley-VCH GmbH


  • acid-promoted electron transfer
  • deuterium kinetic isotope effect
  • inverse kinetic isotope effect
  • proton-coupled electron transfer
  • tunneling effect


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