Computational study of H-abstraction reactions from CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl by Cl atom and OH radical and fate of alkoxy radicals

Understanding the insight into the mechanisms and dynamics of the OH-initiated oxidation of CHF2CF2OCHF2 and the subsequent reactions in the presence of NO and O2

The mechanism and dynamics of CHF₂CF₂OCHF₂ initiated by OH radical evaluated through the density functional theory and variflex code. The solvation pattern of PCM was utilized to analyze the influence of water on the CHF₂CF₂OCHF₂ + OH reaction. The most feasible reaction channel is resulting in the product CF₂CF₂OCHF₂ with H₂O by hydrogen abstraction. The computed rate coefficient is consistent with the experimental data. The results turned out that aqueous water act as a disincentive to the title reaction. In the atmosphere, the computation results testified that OH, H₂O, NH₃ and HCOOH could not accelerate the degradation of the CHF₂CF₂OCHF₂ through OH-initiated in view of the Gibbs free barriers. The research of the follow-up oxidation procedure of the products CHF₂CF₂OCF₂ and CF₂CF₂OCHF₂ with O₂/NO reactions indicated that CF₂O and CHF₂ were the most feasible products. The atmospheric lifetimes of CHF₂CF₂OCHF₂ were in the scope of 71.10-4.74 years in altitude of 0-12 km and at 200-300 K. This research supplies discernment into the conversion of CHF₂CF₂OCHF₂ in a complex environment.

DFT Study of Photochemical Properties and Radiative Forcing Efficiency Features of the Stereoisomers cis- and trans-CHCl═CH-CF3

The accurate assessment of radiative forcing efficiency (RFE) of a greenhouse gas is based on the precise knowledge of its structure and infrared absorption spectrum. The present work investigates the UV-vis absorption spectra and IR absorption spectra that are used for the determination of RFE of the short-lived compounds, cis- and trans-CHCl═CHCF₃ (CTFP). These investigations were carried out with six different density functional theory (DFT) methods B3LYP, CAM-B3LYP, M06, M06-2X, TPSS0, and ωB97X-D associated to the basis set 6-31G(3df). Therefrom, the relative populations of the two states cis and trans for temperatures over the range 220-370 K at 1 atm and along the atmospheric altitude were assessed. It turns out that trans-CTFP is the abundant component between the two states. This review reveals that B3LYP and M06 reproduce well the experimental results of UV-vis spectra of trans-CTFP. As for cis-CTFP, EOM-CCSD is not well fitted by DFT methods. The cis- to trans-CTFP isomerization leads to the red shift for DFT methods and to the blue shift in regard to EOM-CCSD and experimental results. The IR absorption spectra are well fitted by B3LYP over the range 500-1600 cm^-1 and TPSS0 over 1300-2000 cm^-1 for both stereoisomers. Moreover, the root-mean-square errors (RMSEs) of frequencies from experimental data are lower for B3LYP and TPSS0 for both systems. The computed IR absorption band strengths over 500-2000 cm^-1 for cis- and over 600-1800 cm^-1 for trans-CTFP are consistent with the experiment. The relevant descriptor RFEs of the climate effect were calculated using a narrow band model for a constant vertical profile and then corrected with a lifetime factor for different computational methods. The computed values correlate well with the experimental results for both stereoisomers except M06-2X and TPSS0. It is worth noting that, for both systems, the intense radiative forcing spectra are located at frequencies ranging in 1000-1200 cm^-1. The lower forcings of trans-CTFP lying in the atmospheric window region 800-1000 cm^-1 are greater than those of cis-CTFP. Therefore, RFE(trans-CTFP) = 1.127 RFE(cis-CTFP).

Oxidation pathways, kinetics and branching ratios of chloromethyl ethyl ether (CMEE) initiated by OH radicals and the fate of its product radical: an insight from a computational study

The OH-initiated oxidation reactions of chloromethyl ethyl ether (CH2ClOCH2CH3) have been presented by using quantum calculation methods. The Minnesota functional (M06-2X) of the density functional theory method along with a polarization and diffuse 6-311++G(d,p) basis set is chosen for optimization and frequency calculations for H-abstractions from CH2ClOCH2CH3 molecules by OH radicals. Furthermore, the CCSD(T) method along with the same basis set is used for energy refinement of all optimized structures to obtain more accurate energies of the species. Our thermo-chemical calculation results show that the C˙HClOCH2CH3 product radical is more stable, corresponding to hydrogen atom abstraction from the -CH2Cl site, than others while the energy profile results indicate that the H-atom abstracted from the -OCH2 site follows the minimum energy path compared to other channels. The rate constants are computed using canonical transition state theory (CTST) within the temperature range of 250-450 K at 1 atm. The overall rate constant (at 298 K) for the abstraction reactions is found to be consistent with the earlier reported rate constant. The percentage branching ratios of different abstraction channels and the lifetime of chloromethyl ethyl ether are also given herein. We further investigated the unimolecular decomposition pathways of the CH2ClOCH(O˙)CH3 radical and found that unimolecular C-C bond scission is the kinetically and thermodynamically more feasible pathway compared to other unimolecular decomposition reactions.

Thermochemistry and Kinetic Studies on the Autoignition of 2-Butanone: A Computational Study

Unimolecular reactions of alkylperoxy(ROO^•), hydroperoxyalkyl(^•QOOH), and hydroperoxyalkylperoxy(^•OOQOOH) radicals of 2-butanone, which is a potential biofuel molecule, have been studied computationally. These radicals are responsible for the chain branching at low temperature oxidation and play a significant role in modeling the autoignition. The composite CBS-QB3 method was used to study the thermochemistry and energetics of all the species involved. Intrinsic reaction coordinate (IRC) calculations were carried out for all the transition states along various reaction pathways. All the possible reactions like H-migration, ^•OH elimination, and HO^•₂ elimination reactions were studied for these radicals. It was found that, the isomerization of ^•OOQOOH to HOOQOO^• is the most favorable channel, which involves 8- and 9-membered cyclic transition states. However, the decomposition pathway involves the H-migration from carbon to oxygen. The mechanism for the decomposition of all ^•OOQOOH radicals with their potential energy level diagrams are reported. The temperature dependent rate coefficients were also studied using Canonical Variational Transition state theory (CVT) with small curvature tunneling (SCT) in the temperature range of 400-1500 K, which is relevant to the combustion. Thermodynamic parameters for all the reactions involved were calculated. The high barrier (1,3 H-migration) reactions were found to be exothermic and spontaneous, which is unexpected.

Insights into doxycycline adsorption onto graphene nanosheet: a combined quantum mechanics, thermodynamics, and kinetic study

Recently, pharmaceutically active compounds including antibiotics have been detected in drinking water at very low levels, mostly nanogram/liter concentrations, proposing that these materials were unaffected by water treatment processes. Adsorption processes were suggested to play a significant role in the removal of antibiotics. In this study, the adsorption behavior of doxycycline (DC) in aqueous solution was evaluated. The four factors influencing the adsorption of DC onto graphene nanosheet (GNS) were studied. The results showed that initial pH ∼ 6 to 7 and contact time ∼ 200 min are optimum. The monolayer adsorption capacity was reduced with the increasing temperature from 25 to 45 °C. Nonlinear regressions were carried out to define the best fit model for every system. Among various models, the Hill isotherm model represented the equilibrium adsorption data of antibiotics while the kinetic data were well fitted by the Elovich kinetic model. The maximum adsorption capacity (q _max) was 110 mg.g^-1, obtained from the Hill equation. Semiempirical molecular orbital theory was used to investigate the molecular interaction of the adsorption system. The experiments and semiempirical computation have systematically demonstrated that DC could be adsorbed onto GNS by π- π and electrostatic interactions. It was shown that there is a good compromise with the experimental results. Graphical abstract Insights into doxycycline adsorption onto graphene nanosheet: quantum mechanics, thermodynamics, and kinetic study.

Quantum calculation on night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) initiated by NO3 radical

A dual-level quantum chemical calculations have been carried out on the initiation of night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) via H-abstraction by NO3 radical. Within the scope of density functional theory, the electronic structure of all the species involved in the titled reaction has been optimized at M06-2X functional along with 6-31[Formula: see text]G(d,p) basis set. A higher level of couple cluster CCSD(T) method in conjunction with 6-311[Formula: see text]G(d,p) basis set has been used for the refined energy of the species. All minima and saddle states involved in the reaction channel have been characterized on the potential energy surface (PES). From PES, it is confirmed that H-abstraction from methylene (–CH2–) of ethyl (CH3CH2–) part of CH3CH2OCH2CH2Cl follows the minimum energy path. The rate constants (individual and overall) of the titled reaction are obtained using Canonical Transition State Theory (CTST) over the temperature range of 250–350[Formula: see text]K. The atmospheric lifetime and radiative efficiency of the titled molecule have also been estimated, amounting to 0.23 years and 0.024 years, respectively. The Global Warming Potentials of the 2-chloroethyl ethyl ether in 20 years, 100 years and 500 years time horizon were found to be 0.13, 0.04 and 0.01, respectively.