Unravelling the kinetics and molecular mechanism of the degenerate Cope rearrangement of bullvalene

Abstract

The kinetics and molecular mechanism of the gas phase degenerate Cope rearrangement (DCR) of bullvalene have been investigated by applying quantum mechanical calculations.

A Theoretical Study on the Degenerate Cope Rearrangement of Hypostrophene Using the RRKM Theory and Topological Approaches

“…In agreement with the findings of Gimarc et al [7] . the activation energy for DCR of hypostrophene is larger than that of bullvalene [3] . The lack of experimental results has made it impossible to determine the degree of accuracy of CBS kinetic data.…”

“…The lack of experimental results has made it impossible to determine the degree of accuracy of CBS kinetic data. According to the C−C single bond dissociation energy (347 kJ.mol −1 ) and stabilization energy due to the delocalization of the π electrons in allylic radicals (88 kJ.mol −1 ) in the homoaromatic transition structure, the activation enthalpy is estimated to be about 171 kJ.mol −1 [3,38] . The value of the calculated activated enthalpy from the CBS energies revealed that the stabilization energy because of the interactions between the allyl moieties in the homoaromatic transition structure for DCR of hypostrophene is ∼85 kJ.mol −1 , which is smaller than that value for DCR of bullvalene [3] .…”

“…In order to achieve highly accurate energies, ab initio complete basis set‐quadratic Becke3 (CBS‐QB3) [21] and complete basis set‐atomic pair natural orbital (CBS‐APNO) [22] composite methods have been performed to obtain kinetic parameters. The methodologies of the CBS‐QB3 and CBS‐APNO methods have been described in the literature [3,23] . All the calculations have been performed using the Gaussian 16‐A03 program package [24] .…”

“…Bullvalene and hypostrophene are capable of undergoing degenerate Cope rearrangement (DCR) that interconvert among their degenerate isomers. Recently, the kinetic parameters and molecular mechanism of the DCR of bullvalene was studied by authors, [3] while in the present work we aim to focus on the DCR of the hypostrophene. Hypostrophene vocable comes from Greek hypostrophe meaning ‘turning about’ to reflect slow continual Cope rearrangements where the double bonds are eternally passed around the five‐fold rings [4] .…”

“…Moreover, the reliability of the transition state theory (TST) for the calculation of gas phase rate constant has not been considered. The principle motive for this study arises from the preceding work by authors [3] about the DCR of bullvalene. Taking this into account, in the present work temperature‐ and pressure‐dependent rate constant for the gas phase DCR of hypostrophene have been evaluated by means of the Rice‐Ramsperger‐Kassel‐Marcus (RRKM) theory [14] .…”