title: Quantum chemical investigation of low-temperature intramolecular hydrogen transfer reactions of hydrocarbons.
abstract: The B3LYP functional was evaluated as a method to calculate reaction barriers and structure-reactivity relationships for intramolecular hydrogen transfer reactions involving peroxy radicals. Nine different basis sets as well as five other MO/DFT and hybrid methods were used in comparing three reactions to available experimental data. It was shown that B3LYP/6-311+G(d,p) offers a good compromise between speed and accuracy for studies in which thermodynamic and kinetic data of many reactions are required. Sixteen reactions were studied to develop structure-reactivity relationships to correlate the activation energy with the heat of reaction. As long as no structural heterogeneities were present in the transition state ring, a simple Evans-Polanyí relationship was shown to capture the activation energy as a function of heat of reaction for reactions in the 1,5-hydrogen shift family. For peroxy radicals undergoing self-abstraction of a hydrogen atom in the 1,5-position, the activation energy was calculated as E(a) (kcal mol(-1)) = 6.3 + Delta H(rxn) (kcal mol(-1)). For reactions with a carbonyl group embedded in the ring of the transition state, the activation energy of peroxy radicals undergoing self-abstraction was correlated as E(a) (kcal mol(-1)) = 18.1 + 0.74 Delta H(rxn) (kcal mol(-1)). The impact of the size of the transition state ring on the activation energy and pre-exponential factor was also probed, and it was shown that these effects can be described using simple nonlinear and linear fits, respectively.
authors.affiliation: Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208-3120, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Pfaendtner
authors.forename: Xinrui
authors.initials: X
authors.lastname: Yu
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Broadbelt