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Title: Ab initio study for the hydrogen abstraction reactions on toluene and tetralin.

Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are investigated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE pyrolysis through comparison of the reaction barriers with reliable experimental values. We used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. We recomputed selected energy barriers at the B3LYP geometries with the coupled cluster singles and doubles (CCSD) method. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment and the corresponding CCSD energy barriers. The flat potential energy surface around the saddle points causes numerical inaccuracies. We observe the break down of the harmonic approximation in the calculation of low frequencies.
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. ORNL
Publication Date:
OSTI Identifier:
978093
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Preprints of Papers- American Chemical Society, Division of Fuel Chemistry; Journal Volume: 851; Journal Issue: 1-3
Research Org:
Oak Ridge National Laboratory (ORNL)
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 09 BIOMASS FUELS; APPROXIMATIONS; BENZYL RADICALS; FUNCTIONALS; HARMONICS; HYDROGEN; LIGNIN; PERTURBATION THEORY; PHENYL ETHER; POTENTIAL ENERGY; PRODUCTION; PYROLYSIS; TETRALIN; TOLUENE