The cope rearrangement in substituted semibullvalenes as studied by dynamic 13C NMR

Schnieders, Christoph; Müllen, Kläus; Braig, C.; Schuster, H.; Sauer, Jürgen

doi:10.1016/s0040-4039(01)80016-2

Cited by 23 publications

(2 citation statements)

References 14 publications

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“…IR broadband irradiation above 2000cm À1 results in an approximately 1:1r atio of d 2 -2b and d 4 -2b,a nd therefore appro-Scheme2.Representation of the experimentala pproach to studyheavy-atomtunneling in the Coperearrangement of semibullvalenes. [15] 4.8 (4.9)5 .6 [16] 4.0 (4.0)4 .8 (5.1) [17] DDC-C [b] []0 .72-0.72 0.21 [18] 0.75 0.66 [19]…”

Section: Influence Of Substituentsmentioning

confidence: 99%

“…The evaluation of the kinetics data reveals that changing the matrix temperature does not influence the rates significantly (Table 2). With an experimental activation enthalpyo f5 .6 kcal mol À1 , [16] the eightfold increase in temperature in N 2 should result in ar ate acceleration of approx. 10 357 assuming ac onventional thermalreaction, contrary to the observations.…”

Section: Influence Of Substituentsmentioning

confidence: 99%

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Heavy‐Atom Tunneling in Semibullvalenes: How Driving Force, Substituents, and Environment Influence the Tunneling Rates

Schleif

Tatchen

Rowen

et al. 2020

Chemistry A European J

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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.

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