Large Temperature Dependence of Large Kinetic Isotope Effects of Multistep Hydride Reduction of <i>p</i>-Chloranil by NADH Models in Acetonitrile: Proton Tunneling within Loose Radical Ion-Pairs.

ABSTRACT: The temperature dependence of H/D kinetic isotope effects (KIEs) was determined for electron-transfer initiated multistep hydride-transfer reactions of NADH models in acetonitrile to investigate our hypothesis that more rigid systems exhibit smaller isotopic activation energy differences (ΔE_a = E_aD - E_aH). Proton-tunneling occurs in close contact or partially solvent-separated radical ion-pair intermediates. Large KIEs and large ΔE_a's were observed, in contrast to the relatively small KIEs and ΔE_a's typically observed for one-step mechanisms where hydride-tunneling occurs within much tighter charge-transfer complexes. Results support the hypothesis.

SUBMITTER: Pokhrel B 

PROVIDER: S-EPMC12670409 | biostudies-literature | 2025 Nov

REPOSITORIES: biostudies-literature