Revisiting a classic carbocation - DFT, coupled-cluster, and molecular dynamics computations on barbaralyl cation formation and rearrangements.

Density functional theory computations were used to model the formation and rearrangement of the barbaralyl cation (CH ). Two highly delocalized minima were located for CH , one of symmetry and the other of symmetry, with the former having lower energy. Quantum chemistry-based NMR predictions affirm that the lower energy structure is the best match with experimental spectra. Partial scrambling was found to proceed through a symmetric transition structure associated with a barrier of only 2.3 kcal mol. The full scrambling was found to involve a symmetric transition structure associated with a 5.0 kcal mol barrier. molecular dynamics simulations initiated from the CH structure revealed its connection to six minima, due to the six-fold symmetry of the potential energy surface. The effects of tunneling and boron substitution on this complex reaction network were also examined.