Premium
Theoretical investigation on the detailed mechanism of the OH‐initiated atmospheric photooxidation of o ‐xylene
Author(s) -
Huang Mingqiang,
Zhang Weijun,
Wang Zhenya,
Hao Liqing,
Zhao Wenwu,
Liu Xianyun,
Long Bo,
Fang Li
Publication year - 2007
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.21543
Subject(s) - radical , chemistry , isomerization , adduct , photochemistry , bicyclic molecule , p xylene , reaction mechanism , xylene , density functional theory , computational chemistry , medicinal chemistry , organic chemistry , catalysis , benzene
The reaction mechanism for o ‐xylene with OH radical and O 2 was studied by density functional theory (DFT) method. The geometries of the reactants, intermediates, transition states, and products were optimized at B3LYP/6‐31G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single‐point calculations for all the stationary points were carried out at the B3LYP/6‐311++G(2df,2pd) level using the B3LYP/6‐31G(d,p) optimized geometries. Reaction energies for the formation of the aromatic intermediate radicals have been obtained to determine their relative stability and reversibility, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the o ‐xylene oxidation. The results of the theoretical study indicate that OH addition to o ‐xylene forms ipso, meta, and para isomers of o ‐xylene‐OH adducts, and the ipso o ‐xylene adduct is the most stable among these isomers. Oxygen is expected to add to the o ‐xylene‐OH adducts forming o ‐xylene peroxy radicals. And subsequent ring closure of the peroxyl radicals to form bicyclic radicals. With relatively low barriers, isomerization of the o ‐xylene bicyclic radicals to more stable epoxide radicals likely occurs, competing with O 2 addition to form bicyclic peroxy radicals. The study provides thermochemical data for assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from o ‐xylene photooxidation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008