The Theoretical Investigation For The Reactions Of Cyanides With Active Free Radicals

Cyanides （such as hydrogen cyanide, methyl cyanide, ethyl cyanide,Cyanotrifluoromethane, acrylonitrile and so on） are one of the most important classes ofvolatile organic compounds （VOCs）. They are harmful for human and environment when theyrelease into atmosphere. Thus it is especially important for cyanides to be translated andabsorbed. The dominant absorption way is the reactions with radicals （e.g., OH, Cl, F, O）.Experimentally these reactions are hard to research because they are very complex and fast,and could also produce many free radicals and molecules. Therefore, in our paper, quantumchemistry theories and methods are employed to research reaction mechanism and kinetics ofcyanides with active free radicals, and these results would provide some theoretical prospect.During the investigation of reaction dynamics, the difficulty is reaction mechanism andkinetics of multi-channel gas phase reactions. In our paper, the efforts are made to explore andinvestigate these aspects. The results in the thesis are summaried as follows:1. The reaction of H radical with C₂H₅CN had been studied using various quantumchemistry methods. The geometries were optimized at the B3LYP/6-311+G（d,p） andB3LYP/6-311++G（2d,2p） levels. The single-point energies were calculated using G3andBMC-CCSD methods based on B3LYP/6-311++G（2d,2p） geometries. The potential energysurface was obtained at the G3//B3LYP6-311+G（2d,2p） level. Four mechanisms wereinvestigated, namely, hydrogen abstraction, C-addition/elimination, N-addition/eliminationand substitution. The kinetics of this reaction were studied using the transition state theory（TST） and multichannel RRKM methodologies over a wide temperature range of200-3000K.The calculated results indicated that C-addition/elimination channel was the most feasibleover the whole temperature range. The deactivation of initial adduct C₂H₅CHN was dominantat lower temperature; while C₂H₅+HCN was the dominant product at higher temperature.2. The low-lying triplet and singlet potential energy surfaces of the O（³P）+CH₃CNreaction had been studied at the G3（MP2）//B3LYP/6-311+G（d,p） level. On the triplet surface,six kinds of pathways were revealed, namely, direct hydrogen abstraction,C-addition/elimination, N-addition/elimination, substitution, insertion and H-migration.Multichannel RRKM theory and transition state theory were employed to calculate the overalland individual rate constants over a wide range of temperatures and pressures. It waspredicted that the direct hydrogen abstraction and C-addition/elimination on triplet potentialenergy surface were dominant pathways. Major predicted end-products included CH₃+NCOand CH₂CN+OH. At atmospheric pressure with Ar and N₂as bath gases, CH3C（O）N （IM1）formed by collisional stabilization was dominated at T<700K, whereas CH3+NCO producedby C-addition/elimination pathway were the major products at the temperatures between800and1500K; the direct hydrogen abstraction leading to CH₂CN+OH played an important roleat higher temperatures in hydrocarbon combustion chemistry and flames, with estimatedcontribution of64%at2000K. Furthermore, the calculated rate constants were in good agreement with available experimental data over the temperature range300-600K. Thekinetic isotope effect （KIE） had also been calculated for the triplet O（³P）+CH₃CN reaction,and it isn’t important. It was indicated that the singlet reaction exhibited a marked differencefrom the triplet reaction. On the singlet surface, the atomic oxygen could easily insert intoC─H or C─C bonds of CH₃CN, forming the insertion intermediates s-IM8（HOCH₂CN） ands-IM5（CH₃OCN） or added to the carbon atom of-CN group in CH3CN, forming the additionintermediate s-IM1（CH3C（O）N）; both approaches were found to be barrierless.3. Along with the investigation of O（³P） with CH3CN reaction, the quantum chemicalmethods had been employed to investigate the mechanism and kinetics of O（3P and1D） withCF3CN reaction. The singlet and triplet potential energy surfaces had been obtained at theQCISD（T）/6-311+G（2df）//B3LYP/6-311+G（d） level. On the triplet surface, six kinds ofpathways were revealed, namely, direct fluorine abstraction, C-addition/elimination,N-addition/elimination, substitution, insertion and F-migration. The results showed that thereaction should occur mainly through C-addition/elimination mechanism involving thechemically activated CF₃C（O）N*intermediate and the major products are CF₃and NCO. Therate constants for C-addition/elimination channel of O（³P） with CF₃CN reaction had beendetermined by using RRKM statistical rate theory and compared with the experimental data.On the singlet surface, the insertion mechanism was important. The atomic oxygen couldeasily insert into C─F or C─C bond of CF₃CN, forming the insertion intermediates FOCF2CNand CF₃OCN. And O（1D） could add to the carbon or nitrogen atom of-CN group in CF₃CN,forming the addition intermediates CF₃C（O）N and CF₃CNO; both approaches were found tobe barrierless. The decomposition and isomerization of some intermediates were alsoperformed.4. The reaction of OH with CH₂CHCN was revealed to be one of the most significantloss processes of acrylonitrile. Therefore, mechanism and kinetics of the reaction ofacrylonitrile （CH2CHCN） with hydroxyl （OH） had been investigated. CH2CHCN belongsto unsaturated compound, and the reaction of OH with CH₂CHCN is as the same as the OHwith CH₂=CH₂and CH₂=CHCH₃reactions, the pre-reactive complex would be formed.BHandHLYP and M05-2X methods were employed to obtain initial geometries. The reactionmechanism conformed that OH addition to C=C double bond or C atom of-CN group formedthe chemically activated adducts,1-IM1（HOCH₂CHCN）,2-IM1（CH₂HOCHCN）, and3-IM1（CH₂CHCOHN） via low barriers, and direct hydrogen abstraction paths may alsooccur. Temperature-and pressure-dependent rate constants had been evaluated using RRKMtheory. The calculated rate constants were in good agreement with the experimental data. Atatmospheric pressure with N₂as bath gas,1-IM1（OHCH₂CHCN） formed by collisionalstabilization was the major product in the temperature range of200-1200K. The productionof CH₂CCN and CHCHCN via hydrogen abstraction became dominant at high temperatures（1200-3000K）.