Barrier heights for H-atom abstraction by HȮ2 from n-butanol—A simple yet exacting test for model chemistries?
Article first published online: 30 OCT 2009
Copyright © 2009 Wiley Periodicals, Inc.
Journal of Computational Chemistry
Volume 31, Issue 6, pages 1236–1248, 30 April 2010
How to Cite
Black, G. and Simmie, J. M. (2010), Barrier heights for H-atom abstraction by HȮ2 from n-butanol—A simple yet exacting test for model chemistries?. J. Comput. Chem., 31: 1236–1248. doi: 10.1002/jcc.21410
- Issue published online: 12 MAR 2010
- Article first published online: 30 OCT 2009
- Manuscript Revised: 11 AUG 2009
- Manuscript Received: 29 JUL 2009
- An EU Marie Curie Transfer of Knowledge grant. Grant Number: MKTD-CT-2004-517248
- barrier heights;
- H-atom abstraction;
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. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010