The cleavage reactions of the 1-butene and 4,4-dimethyl-1-pentene molecules and their cations, to form neutral and charged hydrocarbon products, are investigated using hybrid Hartree-Fock/density functional theory. In comparison with previous theoretical results (Du et al.), the density functional cleavage and ionization energies, including zero-point vibrational energy, lie in better agreement with experimental and thermochemical data. Assuming vertical ionization processes the mean absolute deviation (MAD) compared with experiment is 3.4 kcal/mol for the reaction sequences studied. Using adiabatic ionization processes instead gives a MAD of 5.2 kcal/mol. The largest deviation from experiment occurs for the cleavage reactions of the neutral parent molecules, where the difference between theory and experiment is up to 12.8 kcal/mol. In addition to reaction energies we also report optimized ground-state structures, and for the radicals studied, isotropic hyperfine coupling constants that are compared to experimental data. It is found that the experimental hyperfine properties of the 1-butene cation can be explained by rotational averaging caused by the flat potential surface for rotation about the C2-C3 bond.Key words: density functional theory (DFT), alkenes, radical cations, bond cleavage, isotropic hyperfine coupling constants.
A case study of density functional theory and domain-based local pair natural orbital coupled cluster for vibrational effects on EPR hyperfine coupling constants: vibrational perturbation theory versus ab initio molecular dynamics
