Theoretical approach of the mechanism of the reactions of chlorine atoms with aliphatic aldehydes

Cl atoms-initiated degradation of 1-Chlorobutane and 2-Chlorobutane: Kinetics, product analysis and atmospheric implications

The relative rate method was employed to investigate the kinetics of the Cl-initiated reactions of 1-chlorobutane (1-CB) and 2-chlorobutane (2-CB) over 263-363 K, and the measured rate coefficients at room temperature are (1.04 ± 0.24) × 10-10 and (5.84 ± 0.27) × 10-11 cm3 molecule-1 s-1, respectively. The Arrhenius equations for the title reactions were derived to be k1-CB + Cl (T = 263-363 K) = (2.77 ± 0.72) × 10-11 exp [(422 ± 79)/T] and k2-CB + Cl (T = 263-363 K) = (1.40 ± 0.32) × 10-11 exp [(415 ± 70)/T] cm3 molecule-1 s-1, respectively. The products were analysed qualitatively using gas chromatography-mass spectrometry (GC-MS), and the reaction mechanism was proposed for the reactions. The rate coefficients for the title reactions were calculated computationally over the temperature range of 200-400 K using canonical variational transition state theory with appropriate tunnelling corrections at CCSD(T)/6-311++G(2d,2p)//BHandHLYP/6-311++G(2d,2p) level of theory to complement our experimentally measured kinetic parameters. The experimental and theoretical data obtained were used to evaluate the impact of the studied molecules in the troposphere.

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C₅ aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18)  ×  10^-10 and (2.07 ± 0.14)  ×  10^-10 cm³/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C₅ aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C₅ aldehyde compounds.

Towards an Understanding of Halide Interactions with the Carbonyl-Containing Molecule CH3 CHO

The anion photoelectron spectra of Cl^- ⋅⋅⋅CD₃ CDO, Cl^- ⋅⋅⋅(CD₃ CDO)₂ , Br^- ⋅⋅⋅CH₃ CHO, and I^- ⋅⋅⋅CH₃ CHO are presented with electron stabilisation energies of 0.55, 0.93, 0.48, and 0.40 eV, respectively. Optimised geometries of the singly solvated species featured the halide appended to the CH₃ CHO molecule in-line with the electropositive portion of the C=O bond and having binding energies between 45 and 52 kJ mol^-1 . The doubly solvated Cl^- ⋅⋅⋅(CH₃ CHO)₂ species features asymmetric solvation upon the addition of a second CH₃ CHO molecule. Theoretical detachment energies were found to be in excellent agreement with experiment, with comparisons drawn between other halide complexes with simple carbonyl molecules.

Understanding the insight into the mechanisms and dynamics of the Cl-initiated oxidation of (CH3)3CC(O)X and the subsequent reactions in the presence of NO and O2 (X = F, Cl, and Br)

In this work, the density functional and high-level ab initio theories are adopted to investigate the mechanisms and kinetics of reaction of (CH₃)₃CC(O)X (X = F, Cl, and Br) with atomic chlorine. Rate coefficients for the reactions of chlorine atom with (CH₃)₃CC(O)F (k₁), (CH₃)₃CC(O)Cl (k₂), and (CH₃)₃CC(O)Br (k₃) are calculated using canonical variational transition state theory coupled with small curvature tunneling method over a wide range of temperatures from 250 to 1000 K. The dynamic calculations are performed by the variational transition state theory with the interpolated single-point energies method at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level of theory. Computed rate constant is in good line with the available experimental value. The rate constants for the title reactions are in this order: k₁<k₂<k₃, suggesting that the effect of halogen substitution on the mechanisms and dynamics is different. The subsequent and secondary reactions for the hydrogen abstraction intermediates are studied involving NO and O₂ molecules in the atmosphere. The atmospheric lifetime and global warming potential (GWP) of (CH₃)₃CC(O)X (X = F, Cl, and Br) are estimated, and it shows that (CH₃)₃CC(O)F have larger GWP value than that of (CH₃)₃CC(O)Cl and (CH₃)₃CC(O)Br. Due to the presence of Cl and Br atoms, the environmental impact of (CH₃)₃CC(O)Cl and (CH₃)₃CC(O)Br may be given more concerns.