| Abstract
| - B3LYP/6-311+G(d,p) computations of the stabilization energies, singlet−triplet energy gaps,and lowest transition states for a set of cyclic alkenylidenes were performed in order to find the strongestinteractions between the C−C double bond and the carbene center. The results suggest that among thealkenylidenes investigated in this study, those with a norbornenylidene structure represent strongly stabilizedcarbenes with a reduced reactivity toward intermolecular reactions. Further stabilization is found when thedouble bond is electron-rich or pyramidalized. Thus, for the rearrangement of syn-34 to take place, anactivation barrier of about 22 kcal/mol needs to be overcome. The inclination to undergo a retro-Skattebølrearrangement, which to our knowledge has never been observed experimentally, is characteristic for highlystabilized foiled carbenes.
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