title: Hydrogen Tunneling above Room Temperature Evidenced by Infrared Ion Spectroscopy.
abstract: While hydrogen tunneling at elevated temperatures has, for instance, often been postulated in biochemical processes, spectroscopic proof is thus far limited to cryogenic conditions, under which thermal reactivity is negligible. We report spectroscopic evidence for H-tunneling in the gas phase at temperatures around 320-350 K observed in the isomerization reaction of a hydroxycarbene into an aldehyde. The charge-tagged carbene was generated in situ in a tandem mass spectrometer by decarboxylation of oxo[4-(trimethylammonio)phenyl]acetic acid upon collision induced dissociation. All ion structures involved are characterized by infrared ion spectroscopy and quantum chemical calculations. The charge-tagged phenylhydroxycarbene undergoes a 1,2-H-shift to the corresponding aldehyde with an half-life of about 10 s, evidenced by isomer-selective two-color (IR-IR) spectroscopy. In contrast, the deuterated (OD) carbene analogue showed much reduced 1,2-D-shift reactivity with an estimated half-life of at least 200 s under the experimental conditions, and provides clear evidence for hydrogen atom tunneling in the H-isotopologue. This is the first spectroscopic confirmation of hydrogen atom tunneling governing 1,2-H-shift reactions at noncryogenic temperatures, which is of broad significance for a range of (bio)chemical processes, including enzymatic transformations and organocatalysis.
authors.affiliation: Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Schäfer
authors.affiliation: Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Peckelsen
authors.affiliation: Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Paul
authors.affiliation: Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.
authors.forename: Jonathan
authors.identifier: 0000-0001-9537-4117
authors.initials: J
authors.lastname: Martens
authors.affiliation: Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.|Van't Hoff Institute for Molecular Sciences, University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.affiliation: Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.affiliation: Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany.
authors.forename: Albrecht
authors.identifier: 0000-0003-0470-7428
authors.initials: A
authors.lastname: Berkessel
authors.affiliation: Department of Chemistry, University of Sheffield , Sheffield S3 7HF, U.K.
authors.forename: Anthony J H M
authors.identifier: 0000-0003-4803-3488
authors.initials: AJHM
authors.lastname: Meijer