Rearrangements on the C6H6 Potential Energy Surface and the Topomerization of Benzene

摘要: The benzene potential energy hyperface was examined employing hybrid Hartree−Fock/density functional theory (B3LYP), second-order perturbation (MP2), and the coupled-cluster method with single, double, perturbative triple excitations [CCSD(T)] in conjunction DZP TZ2P basis sets. All stationary points were characterized by harmonic vibrational frequency analyses; intrinsic reaction coordinates calculated for all transition structures at B3LYP/DZP. Final energies evaluated CCSD(T)/DZP//B3LYP/DZP level corrected T = 1373 K. There are three competing mechanisms high-temperature intramolecular topomerization of [1,2-13C2]benzene to [1,3-13C2]- [1,4-13C2]benzene:  (a) ring contraction benzvalene (ΔG ⧧ 93.5 kcal mol-1) followed opening benzene; (b) degenerate rearrangement via a 1A‘‘ prefulvene TS 95.0 mol-1 relative benzene) generating [1,4-13C2]benzene as primary product [1,2-13C2]benzen...