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Title:Barrier heights for H-atom abstraction by HȮ2 from n-butanol—A simple yet exacting test for model chemistries?
Authors:Gráinne Black, John M. Simmie, 2010
Abstract: The barrier heights involved in the abstraction of a hydrogen atom from n-butanol by the hydroperoxyl radical have been computed with both compound (CBS-QB3, CBS-APNO, G3) and coupled cluster methods. In particular, the benchmark computations CCSD(T)/cc-pVTZ//MP2/6-311G(d,p) were used to determine that the barrier heights increase in the order α <γ < β < δ < OH. Two prereaction hydrogen-bonded complexes are formed, one of which connects the TGt conformer of n-butanol to the α and β transition states and the other connects to the γ and OH channels from the TGg conformer. Four postreaction complexes were also found which link the transition states to the products, hydrogen peroxide + C4H9O radical. Abstraction from the terminal δ carbon atom does not involve either a pre or postreaction complex. A number of DFT functionals—B3LYP, BMK, MPWB1K, BB1K, MPW1K, and M05-2X—were tested to see whether the correct ranking could be obtained with computationally less expensive methods. Only the later functional predicts the correct order but requires a basis set of 6-311++G(df,pd) to achieve this. However, the absolute values obtained do not agree that well with the benchmarks; the composite G3 method predicts the correct order and comes closest (≤ 2 kJ, mol −1) in absolute numerical terms for H-abstraction from carbon.
ICHEC Project:BurnQuest: Towards a World Class Combustion Chemistry Centre
Publication:Journal of Computational Chemistry 31(6): 1236–1248
URL: http://www3.interscience.wiley.com/journal/122670110/abstract
Keywords: barrier heights;H-atom abstraction;kinetics;functionals
Status: Published

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