Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study

Abstract

The relative rate (RR) technique was used for the measurement of OH-initiated photooxidation reactions of ethyl 2methylpropionate (E2MP) and ethyl 2,2-dimethylpropionate (E22DMP) in the temperature range of 268−363 K at 760 Torr. In addition to this, the thermodynamic and kinetic parameters for the title reactions were theoretically investigated using CCSD(T)/cc-pVTZ//M06-2X/6-311+ +G(2d,2p) level of theory in the temperature range of 200−400 K using canonical variational transition state theory (CVT) in combination with small curvature tunneling (SCT) method. The rate coefficients at (298 ± 2) K were measured to be k E2MP+OH = (2.71 ± 0.79) × 10 −12 cm 3 molecule −1 s −1 and k E22DMP+OH = (2.58 ± 0.80) × 10 −12 cm 3 molecule −1 s −1 . The degradation mechanisms for the title reactions were investigated in the presence of O 2 using gas chromatography with mass spectrometry (GC-MS) and gas chromatography with infrared spectroscopy (GC-IR). From the recognized products, the possible product degradation mechanisms were predicted. In addition to this, the atmospheric lifetimes (ALs), lifetime-corrected radiative forcing (RF), global warming potential (GWPs) and photochemical ozone creation potentials (POCPs) were calculated to further understand the environmental impact of these molecules on the Earth's troposphere.

Photo-oxidation reaction of tert-butyl chloride with OH radicals and Cl atoms in the troposphere and its implications

“…52 Another important distinction between the reactions of VOCs with OH, Cl and Br is their trends in reaction enthalpies. The reactions involving H-abstraction from VOCs by OH radicals and Cl atoms tend to be exothermic [53][54][55] whereas they are usually endothermic for the reactions with Br atoms. 35 Reactions with OH radicals which produce water molecules are known to be highly exothermic compared to Cl-initiated reactions.…”