Barrier heights for H-atom abstraction by HȮ2 from n-butanol—A simple yet exacting test for model chemistries?
✍ Scribed by Gráinne Black; John M. Simmie
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 455 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0192-8651
No coin nor oath required. For personal study only.
✦ Synopsis
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 + C~4~H~9~O 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