Theoretical study of H-atom abstraction reactions from CHCHOCHCH, CHFCFOCHCF and CFCHOCH by NO radical & subsequent degradation.

The nocturnal reactions of CHCHOCHCH, CHFCFOCHCF and CFCHOCH initiated by NO radicals are important sources of alkyl radicals and nitric acids. In this paper, the thermodynamics and kinetics of CHCHOCHCH, CHFCFOCHCF and CFCHOCH induced by NO radical in gas phase are studied in detail by BHandHLYP method combined with 6-311G(d,p) basis set, and the single point correction is calculated by relatively accurate CCSD(T) method. In the temperature range of 200-400 K, the rate constants of title reactions are fitted to the three-parameter Arrhenius formula: k = 1.13 × 10Texp(1675.99/T) k = 2.23 × 10Texp(-4476.24/T) k = 5.63 × 10Texp(-9344.12/T) All the rate constants calculated by the canonical variational transition state theory and the small curvature tunneling are basically consistent with the limited experimental data. By comparing the reaction rate constants of ethyl ether and its isomer methyl propyl ether with NO radical at 293 ± 2 K, the higher the symmetry is, the faster the reaction rate of ether is. Thermodynamic calculations and kinetic data of the title reactions indicate that the H-abstraction reactions at the -OCH- sites are the main reaction pathways. The thermodynamic and kinetic data of the reaction CHCHOCHCH, CHFCFOCHCF with NO radical, showing that the reaction activity could be reduced due to the addition of fluorine atoms, which is further verified by the enthalpies, Gibbs free energies of the title reactions and C-H bond dissociation energies of the CHCHOCHCH, CHFCFOCHCF and CFCHOCH molecules. The reaction thermodynamics and kinetics are determined, and the formation mechanisms of the products are proposed, which are crucial to determine the influence of CHCHOCHCH, CHFCFOCHCF and CFCHOCH on air quality, as well as its atmospheric lifetime and durability. The atmospheric lifetimes of CHCHOCHCH, CHFCFOCHCF and CFCHOCH are evaluated in the NO-concentration range of 5 × 10-2 × 10 molecule cm to fully consider the effects of different regions on their nocturnal migration. The radiation efficiency and global warming potentials (GWPs) have been reported. The products of title reaction CHCHOCHCH, CFCHOCFCHF and CFCHOCH are further oxidized into organic nitrates in the presence of O and NO. Organic nitrites can be isomerized into organic nitrates or degraded to form CHC(O•)HOCHCH, CFC(O•)HOCFCHF and CHC(O•)HOCF alkoxy radicals and NO. This work provides deep insight into the night migration and transformation mechanism of the three ethers.