The Mystery of the Benzene‐Oxide/Oxepin Equilibrium—Heavy‐Atom Tunneling Reversed by Solvent Interactions. Issue 46 (30th September 2020)

• Record Type: Journal Article
• Authors: Schleif, Tim; Prado Merini, Melania; Sander, Wolfram
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 46(2020)
• Page Start: 20318
• Page End: 20322
• Publication Date: 2020-09-30
• Subjects: halogen bonding -- matrix isolation -- noncovalent interactions -- rearrangement -- tunneling; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202010452
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The equilibrium between benzene oxide (1 ) and oxepin (2 ) is of large importance for understanding the degradation of benzene in biological systems and in the troposphere. Our studies reveal that at cryogenic temperatures, this equilibration is governed by rare heavy‐atom tunneling. In solid argon at 3 K, 1 rearranges to 2 via tunneling with a rate constant of approximately 5.3×10 −5 s −1 . Thus, in a nonpolar environment, 2 is slightly more stable than 1, in agreement with calculations at the CCSD(T) level of theory. However, if the argon is doped with 1 % of H2 O or CF3 I as typical hydrogen or halogen bond donors, respectively, weak complexes of 1 and 2 are formed, and now 2 is tunneling back to form 1 . Thus, by forming non‐covalent complexes, 1 becomes slightly more stable than 2 and the direction of the heavy‐atom tunneling is reversed. Abstract : Matrix‐isolation studies reveal a long‐standing misconception about the benzene‐oxide/oxepin equilibrium by confirming the intrinsic greater stability of oxepin. They also find that this equilibration proceeds via a rare heavy‐atom tunneling process at cryogenic temperatures. Finally, the solvent control of heavy‐atom tunneling is demonstrated for the first time as the direction of the reaction is inverted in the presence of Lewis acids.