期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 16, 期 33, 页码 17908-17917出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4cp02027h
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资金
- National Natural Science Foundation of China [21177041]
- Ministry of Environmental Protection of China [201409019]
The atmospheric oxidation mechanism of 1,2,4-trimethylbenzene (1,2,4-TMB) initiated by OH radicals is investigated using quantum chemistry calculations at M06-2X and ROCBS-QB3 levels. The calculations show that the initiation of the reaction is dominated by OH addition to C-1, C-3 and C-5 to form 1,2,4-TMB-OH adducts R1, R3, and R5 with branching ratios of 0.22, 0.19, and 0.38, respectively, using ROCBS-QB3 energies. In the troposphere, the adducts react with O-2 by irreversible H-abstraction to form phenolic compounds and by reversible addition to TMB-OH-O-2 peroxy radicals, which will cyclize to bicyclic radicals, similar to those in benzene, toluene, and xylenes. The bicyclic radicals can further recombine with O-2 to generate bicyclic peroxy and alkoxyl radicals. The bicyclic alkoxyl radicals would break the ring directly to form 1,2-dicarbonyl products and unsaturated 1,4-dicarbonyl co-products, or undergo another cyclization to form an epoxy group, followed by the ring-breakage to form 1,2-dicarbonyl products and epoxy-1,4-dicarbonyl co-products. The predicted yields of products agree reasonably with the previous experimental measurements, while considerable discrepancies also exist for the yields of nitrates, biacetyl, 4-oxo-2-pentenal, and butenedial, etc. Our mechanism also predicts a new type of epoxy-1,4-dicarbonyl compounds with a total yield of similar to 0.32. The epoxy-1,4-dicarbonyl compounds have not been suggested or reported in previous studies.
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