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Theoretical Study on the Mechanisms of Reactions of Formaldehyde or Formacyl Radical and Active Radicals

Author: ZhuYuanQiang
Tutor: LiLaiCai
School: Sichuan Normal University
Course: Materials Science
Keywords: Peroxy radical HCHO HCO radical Reaction mechanism Transition state G3 method
CLC: O621.25
Type: Master's thesis
Year: 2005
Downloads: 132
Quote: 1
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Abstract


In the first section of this thesis, the mechanisms of reactions between formaldehyde or formacyl radical and active radicals or small molecules has been studied by the quantum-chemical calculation programs with big basis sets at the room temperatures. In this section, we study the following three reaction systems:1. Reaction of the HCO radical and HO2 radical;2. Reaction of the HCHO and HO2, OH, H radicals;3. Reaction of the HCHO and HO2 molecule.We optimize the geometries of all stationary points in the systems by using density functional theory (DFT) B3LYP method. Our purpose of this study is to make clear the complex processes of reactions involving formaldehyde or formacyl radical and to find out the main channels and the main products. It is theoretically helpful for the experimental scientists and atmospherical purification. Gaussian-3 (G3), which has been developed recently and regarded as one of the most accurate methods, is employed in this thesis. The results of the study are: the HCO+HO2 reaction has six possible exothermic channels, the major one of whichis HC0+HO,-*TS2—IM2—HCHO+Oz The other channels will compete with the major one by forming a very stable intermediate firstly. In the HCH0+H02 reaction, there are four possible endothermic channels, and the main one is HCHO+ HQ,—IM1—TS1—IM2+H2QI-’TS2-mA—HA-KXH1. Products such as H202, CO and H atom are easier to get formed than the others. The HCHO+HO reaction has three possible exothermic channels, and the main one is HCHO+OH—TM9—TS13—IM2(HCO)+H2. The HCHO+H reaction has three possible exothermic channels, and the main channel is HCHO+H—TS19-*IM2 (HCO) +H2. The HCHO+NO2 reaction has three possible exothermic channels, and the main one is O(WKVIMl-*TSl-*IM2-IM6+C0—TS4+C0-H0N0+C0.In the second section of this thesis, we study the behavior of atmorspheric chemistry of oxidant of CH3CHF2 (R152a), which is an environmental friendly replacement of CFC s. When R152a reacts with OH radical, there are organic peroxy radicals formed such as CH3CFA. Moreover, peroxy radicals are the main products when the organic compounds oxidated by oxidatants at the presence of light. The reactions between organic peroxy radicals and other chemicals are one of the most important chemical circulations of the photochemical air pollution. For above reasons, we study the mechanism of the reaction between CH3CF202 and H02radical, in which, we find two possible reaction channels, of which the main one is OtCFA+HQj—IM1—TS1—CHCFjOOH+a.All formaldehyde^ formacyl radical and organic peroxy radicals play an important part in the chemical circulations and will affect human health as well as environment. At present, the study of the chemical behavior of peroxy radicals is the focuses in atmospherical field. The results can contribute to the enrichment of the database of this field.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Properties of organic compounds > Chemical properties of organic reactions
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