Heavy‐Atom Tunneling in Semibullvalenes: How Driving Force, Substituents, and Environment Influence the Tunneling Rates. Issue 46 (28th July 2020)

• Record Type: Journal Article
• Authors: Schleif, Tim; Tatchen, Jörg; Rowen, Julien F.; Beyer, Frederike; Sanchez‐Garcia, Elsa; Sander, Wolfram
• Is Part Of: Chemistry. Volume 26:Issue 46(2020)
• Page Start: 10452
• Page End: 10458
• Publication Date: 2020-07-28
• Subjects: confinement -- heavy-atom tunneling -- matrix isolation -- SCT calculations -- solvent effects; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202001202
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The Cope rearrangement of selectively deuterated isotopomers of 1, 5‐dimethylsemibullvalene 2 a and 3, 7‐dicyano‐1, 5‐dimethylsemibullvalene 2 b were studied in cryogenic matrices. In both semibullvalenes the Cope rearrangement is governed by heavy‐atom tunneling. The driving force for the rearrangements is the small difference in the zero‐point vibrational energies of the isotopomers. To evaluate the effect of the driving force on the tunneling probability in 2 a and 2 b, two different pairs of isotopomers were studied for each of the semibullvalenes. The reaction rates for the rearrangement of 2 b in cryogenic matrices were found to be smaller than the ones of 2 a under similar conditions, whereas differences in the driving force do not influence the rates. Small curvature tunneling (SCT) calculations suggest that the reduced tunneling rate of 2 b compared to that of 2 a results from a change in the shape of the potential energy barrier. The tunneling probability of the semibullvalenes strongly depends on the matrix environment; however, for 2 a in a qualitatively different way than for 2 b . Abstract : The influence of cryosolvation and confinement on the heavy‐atom tunneling process in the Cope rearrangement of selectively deuterated dicyanosemibullvalene derivatives has been studied. The experimentally determined reaction rates nicely agree with TST+SCT calculations and provide insights into the compensation of barrier heights and widths as determining factors of tunneling processes (see figure).