Gibbs Free Energy Of Reaction Research Articles

Free radical scavenging mechanism of 1,3,4-oxadiazole derivatives: thermodynamics of O–H and N–H bond cleavage

The thermodynamics of free radical scavenge of 1,3,4-oxadiazole derivatives towards oxygen-centred free radicals were investigated by the density functional theory (DFT) method in the gas phase and aqueous solution. Three mechanisms of free radical scavenge namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were considered. The antioxidant descriptors that characterize these mechanisms such as, bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) were evaluated. The sequence of electron donation as predicted by the HOMO results were in good agreement with the sequence of ETE for the considered molecules at their favoured sites of free radical scavenge. The reaction Gibbs free energy for inactivation of the selected peroxyl radicals, show that 1,3,4-oxadiazole antioxidants are more efficient radical scavengers by HAT and SPLET mechanisms than SET-PT mechanism in vacuum. In aqueous solution, the SET-PT mechanism was observed to be the dominant reaction pathway.

Uranosphaerite: Crystal structure, hydrogen bonding, mechanics, infrared and Raman spectroscopy and thermodynamics

A detailed structural, spectroscopic, mechanical and thermodynamic characterization of the bismuth uranyl-oxide hydroxy-hydrate mineral uranosphaerite, Bi(UO2)O2OH, is obtained using the X-ray diffraction and infrared and Raman spectroscopic techniques and first principles solid-state methods based on density functional theory employing plane wave basis sets and pseudopotentials. The full crystal structure of uranosphaerite, including the positions of the hydrogen atoms within the corresponding unit cell, is determined by the first time from X-ray diffraction data taken from a natural crystal sample from Menzenschwand uranium deposit (Germany). The crystal structure obtained from X-ray diffraction is confirmed by using the first principles methodology. The computed structural parameters and X-ray diffraction pattern are in excellent agreement with their experimental counterparts. From the energy-optimized crystal structure, the mechanical and dynamical stability of uranosphaerite is studied and a rich set of mechanical properties are determined. Uranosphaerite is shown to display the negative Poisson's ratio phenomenon. The experimental infrared spectrum is recorded from a natural sample from Schneeberg (Germany) and the Raman spectrum is collected from two crystal samples from Hagendorf and Schneeberg localities (Germany). Both spectra are also determined using density functional perturbation theory and compared with the observed spectra. Since the computed and experimental spectra have a very high degree of consistence, the infrared and Raman bands are completely assigned using a normal coordinate analysis of the theoretical vibrational results. The spectral zone from 1000 to 3000 cm−1 in the infrared and Raman spectra is shown to be plagued of low intensity combination bands. Eleven and eight combination bands are identified in the infrared and Raman spectra, respectively. The fundamental thermodynamic functions of uranosphaerite are computed as a function of temperature using phonon calculations. The computed specific heat and entropy at 298.15 K are 147.7 and 180.4 J·K−1·mol−1, respectively. The computed thermodynamic parameters are used to determine the corresponding thermodynamic properties of formation in terms of the elements as a function of temperature and the Gibbs free energies of reaction of a series of reactions involving uranosphaerite and a representative subset of the most important secondary phases of spent nuclear fuel. The relative stability of uranosphaerite with respect to these phases as a function of temperature and under different concentrations of hydrogen peroxide is reported.

Reducing Oxygen Evolution Reaction Overpotential in Cobalt‐Based Electrocatalysts via Optimizing the “Microparticles‐in‐Spider Web” Electrode Configurations

Sluggish kinetics of the multielectron transfer process is still a bottleneck for efficient oxygen evolution reaction (OER) activity, and the reduction of reaction overpotential is crucial to boost reaction kinetics. Herein, a correlation between the OER overpotential and the cobalt-based electrode composition in a "Microparticles-in-Spider Web" (MSW) superstructure electrode is revealed. The overpotential is dramatically decreased first and then slightly increased with the continuous increase ratio of Co/Co3 O4 in the cobalt-based composite electrode, corresponding to the dynamic change of electrochemically active surface area and charge-transfer resistance with the electrode composition. As a proof-of-concept, the optimized electrode displays a low overpotential of 260 mV at 10.0 mA cm-2 in alkaline conditions with a long-time stability. This electrochemical performance is comparable and even superior to the most currently reported Co-based OER electrocatalysts. The remarkable electrocatalytic activity is attributed to the optimization of the electrochemically active sites and electron transfer in the MSW superstructure. Theoretical calculations identify that the metallic Co and Co3 O4 surface catalytic sites play a vital role in improving electron transport and reaction Gibbs free energies for reducing overpotential, respectively. A general way of boosting OER kinetics via optimizing the electrode configurations to mitigate reaction overpotential is offered in this study.

Correlation between Equilibrium Constant and Stabilization Energy: A Combined Approach Based on Chemical Thermodynamics, Statistical Thermodynamics, and Density Functional Reactivity Theory.

In the present work, an attempt is made to establish the correlation between equilibrium constant and stabilization energy [ΔESE(AB)] generated from density functional reactivity theory (DFRT). The reactions chosen here are of type A + B ⇌ AB (i.e., adduct formation type) between an electron acceptor, A, and an electron donor, B. The representative acceptors are methyltrioxorhenium (MTO) and substituted benzaldehydes whereas donors are 26 mono- and bidentate ligands (having N-donors) and semicarbazide. The trends of experimentally generated equilibrium constant (K) values match with those of ΔESE(AB) in most of the cases, both in gas phase as well as in solvent. Justification of this reliable correlation is provided analytically using the expressions of standard Gibbs free energy of reaction (i.e., ΔrGθ) and the stabilization energy expression generated by DFRT. A further analytical explanation (albeit not very rigorous) is provided through statistical thermodynamics showing how equilibrium constant (K) is related to ΔESE(AB) for reactions of the type A + B ⇌ AB, where either A or B is a common species.

Mineralization of the Luanling gold deposit in the southern margin of the North China Craton: Insights from mineralogy and mineral chemistry of sulfides, tellurides and oxides

The Luanling gold deposit, a typical Te‐Au deposit in the Xiong'er terrane, the southern margin of the North China Craton, contains two types of ores, namely altered rock‐type and quartz vein‐type ores. Gold is hosted by pyrite and As‐bearing pyrite in the altered rock‐type ores, whereas tellurides are the main gold carriers in the quartz vein‐type ores. In order to investigate their origins, we calculated the Gibbs free energies of formation and reaction of related sulfides, tellurides and oxides from different ore types. The phase diagrams of these minerals were constructed at 300 °C, a temperature at which gold was mainly precipitated in the Luanling deposit. According to phase relations among sulfides, logfS2(g) is constrained between −10.4 and −6.5. In addition, we propose that [Au(HS)2]− was the dominant carrier of gold in ore‐forming fluid, and its decomposition formed pyrite and arsenian pyrite, in which gold mainly exists as an invisible phase. In the quartz vein‐type ores, logfTe2(g) and logfO2(g) are constrained to range from −13.68 to −7.9 and −36.8 to −31.1, respectively, based on the phase relations between tellurides, sulfides and oxides, and gold was mainly transported as [Au(HTe)2]− and its break down formed gold‐bearing, including sylvanite, petzite and Au‐Ag‐tellurides. Sylvanite and petzite, the two stable Au‐Ag tellurides, were probably precipitated primarily from hotter ore‐forming fluids. According to phase relations among tellurides, the two phases were decomposed into native gold, hessite and more stable Au‐Ag‐tellurides with the changes of physicochemical conditions in the later stages. In addition, we proposed that the ore‐forming fluids relevant to the altered rock‐ and the quartz vein‐type ores were from the same source and continuously evolved.

Theoretical study on double-atom catalysts supported with graphene for electroreduction of nitrogen into ammonia

Developing electrocatalyst with high catalytic activity for the nitrogen reduction reaction (NRR) is the key step to accelerate the application of electrocatalytic nitrogen fixation. Eight kinds of double-atom Fe catalysts supported with graphene-based substrate (Fe-TMDA/GS, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) were constructed for electroreduction of nitrogen into ammonia. The bonding mechanism of Fe-transition metal dimer on substrates was studied from the perspectives of orbital hybridization and electron transfer. Based on the analysis of reaction paths and Gibbs free energy variation, the potential determining step of the NRR is the transfer process of the first H+/e− pair. Fe-TiDA/GS has the highest NRR catalytic activity among the eight kinds of Fe-TMDA/GS, with a Gibbs energy variation of 0.88 eV. Based on the analysis of electron density difference, band structure and work function, electron transfer is the main factor affecting nitrogen adsorption, and the second metal atom improves the catalytic activity of NRR through promoting electron transfer between N2 and the graphene surface. This theoretical research provides new insights into developing highly efficient electrocatalyst for NRR.

DFT study of new P-heterocyclic silylenes

Following our quest for new divalents, we report the synthesis of P-heterocyclic silylenes (PHSis) by adding from one to four phosphorous atoms to saturated cyclopentasilylene (1) and unsaturated cyclopentasilylene-3-ene (1') resulting in respective PHSis (2—10 and 2'—10', respectively) and their study at the B3LYP/6-311++G** level of theory. Stabilities of 1—10 and 1'—10' assumed as the energy gaps between the singlet (s) and triplet (t) states (DEs-t) are compared and contrasted. With increasing number of phosphorous atoms, singlet-triplet energy gap (DEs-t), nucleophilicity (N), electrophilicity (w), chemical potential (m), band gap (DEH-L), positive natural bond orbital (NBO) charge on the Si atom, and reactivity decrease. Changes in the hydrogenation enthalpy (DHHyd) of 1—10 and 1'—10' show negative values indicating that the formation of hydrogenated divalent silylenes is exothermic (1H—10H and 1H'—10H', respectively). The positive overall change in the Gibbs free energy of reaction (DGover for the conversion of 1'—10' to 1—10, respectively) confirms that every 1'—10' is more stable than its corresponding 1—10.

Effects of a Ni cocatalyst on the photocatalytic hydrogen evolution reaction of anatase TiO2 by first-principles calculations

Loading Nin clusters on anatase TiO2 surfaces remarkably reduces the Gibbs free energy of the photocatalytic hydrogen evolution reaction.

A coumarin derivative-Cu2+ complex-based fluorescent chemosensor for detection of biothiols.

Herein, a novel fluorescent sensor has been developed for the detection of biothiols based on theoretical calculations of the stability constant of the complex between a Cu2+ ion and (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-7-(diethylamino) coumarin (BDC) as a fluorescent ligand. In this study, on the basis of density functional theory method, the Gibbs free energy of ligand-exchange reaction and the solvation model were carried out using thermodynamic cycles. The obtained results are in good agreement with the experimental data. The BDC–Cu2+ complex can be used as a fluorescent sensor for the detection of biothiols in the presence of non-thiol containing amino acids, with a detection limit for cysteine at 0.3 μM. Moreover, theoretical calculations of excited states were used to elucidate variations in the fluorescence properties. The computed results show that the excited doublet states D2 and D1 are dark doublet states, which quench the fluorescence of the complex.

Structure elucidation and formation mechanistic study of a methylene-bridged pregabalin dimeric degradant in pregabalin extended-release tablets.

During the pharmaceutical development of pregabalin extended-release tablets, an unknown degradant at a relative retention time (RRT) of 11.7 was observed and its nominal amount exceeded the ICH identification threshold in an accelerated stability study. The aim of this study is to identify the structure and investigate the formation mechanism of this impurity for the purpose of developing a chemically stable pharmaceutical product. By utilizing multi-stage LC-MS analysis in conjunction with mechanism-based stress study, the structure of the RRT 11.7 impurity was rapidly identified as a dimeric degradant that is caused by dimerization of two pregabalin molecules with a methylene bridging the two pregabalin moieties. The structure of the dimer was confirmed by 1D and 2D NMR measurement. The formation pathway of the dimeric degradant was also inferred from the mechanism-based stress study, which implicated that the bridging methylene could originate from formaldehyde which might be the culprit that triggers the dimerization in the first place. The subsequent API-excipients compatibility study indicated that the degradant was indeed formed in the compatibility experiments between pregabalin API and two polymeric excipients (PEO and PVPP) that are known to contain residual formaldehyde, but only in the co-presence of another excipient, colloidal silicon dioxide (SiO2). The kinetic behavior of the degradant formation was also investigated and two kinetic models were utilized based on the Arrhenius and Eyring equations, respectively, to calculate the activation energy (Ea) as well as the enthalpy of activation (△H‡), entropy of activation (△S‡), and Gibbs free energy (△G‡) of the degradation reaction. The results of this study would be useful for the understanding of similar dimeric degradant formation in finished products of drug substances containing primary or secondary amine moieties.

Antioxidant vs. pro‐oxidant activities of quercetin in aqueous phase: A Density Functional Theory study

AbstractThe antioxidant potential of quercetin (Quer) has been investigated for its radical scavenging activity and Cu(II) ion chelating one. Two intrinsic reactivities including bond dissociation enthalpy (BDE) and proton affinity (PA) were systematically calculated in water at the M05‐2X/6‐311++G(d,p) level of theory. All possible hydrated Quer–Cu(II) complexes were also performed to consider its indirect antioxidant activity via the meal ion chelation capacity. Furthermore, reaction enthalpies as well as Gibbs free energies of reactions between Quer‐Cu(II) complexes with O2•‐ and ascorbate anion (Asc‐) in forming corresponding Quer‐Cu(I) ones have also been investigated to draw the larger picture on reduction potential of Cu(II)to Cu(I) ions which may involve in Fenton‐like reactions leading to HO• radical formation.

Thiols in Natural Organic Matter: Molecular Forms, Acidity, and Reactivity with Mercury(II) from First-Principles Calculations and High Energy-Resolution X-ray Absorption Near-Edge Structure Spectroscopy

Thiol functional groups in natural organic matter form strong complexes with Hg(II) and other soft metal cations and therefore are an important component of sulfur and metal cycling in the environment. However, characterizing thiol reactivity is difficult because natural organic molecules are complex both in composition and molecular structure. Here, reactivity was assessed by calculating the Gibbs free energies of thiolation and thiol deprotonation reactions for model structures considered to form during abiotic sulfurization of natural organic matter. Gaussian calculations were performed at the CCSD(T) level of theory. Thiol addition is predicted to be faster by as much as 8 orders of magnitude on unsaturated cyclic structures rich in ketone and ether linkages than on open-chain carbonyl structures. The pKa values of thiols added to carboxyl-rich alicyclic molecules are predicted to be above 10, whereas pKa values of thiols bonded to lignin-derived polyhydroxyphenols are predicted to be between 2 and 6....

Kinetic Study on Esterification of Acetic Acid with Isopropyl Alcohol Catalyzed by Ion Exchange Resin.

Esterification kinetics on acetic acid with isopropyl alcohol was studied in an intensified fixed bed reactor at 333–353 K with Amberlyst 36 Wet. The effects of volume flow rate, molar ratio of reactants, catalyst loading, and operating temperature were investigated and optimized. The method of UNIFAC was applied to calculate the activity coefficient of each component for correcting the nonideality of the solution. Reaction enthalpy, entropy, and Gibbs free energy were calculated in different cases. The pseudohomogeneous model, Eley–Rideal model, and Langmuir–Hinshelwood–Hougen–Watson model were used to establish kinetic equations of the reaction conducted in the IFBR. It was proved that the LHHW model can accurately describe the esterification kinetics in the intensified fixed bed reactor.

In silico design of hydrazone antioxidants and analysis of their free radical-scavenging mechanism by thermodynamic studies

BackgroundAntioxidants are very crucial in maintaining the normal function of body cells, as they scavenge excess free radical in the body. A set of hydrazone antioxidants was designed by in silico screening. The density functional theory (DFT) method was employed to explore the reaction energetics of their free radical-scavenging mechanism. With the aid of the developed quantitative structure-activity relationship (QSAR) model for hydrazone antioxidants, the structure and antioxidant activity of these compounds were predicted. Three potential reaction mechanisms were investigated, namely, hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA), electron transfer enthalpy (ETE) and Gibbs free energy that characterize the various steps in these mechanisms were calculated in the gas phase.ResultsA total of 25 hydrazone antioxidants were designed, in which the molecule MHD 017 gave the best antioxidant activity. Among the tested molecules, MHD 017 at the 10-OH site gave the best results for the various thermodynamic parameters calculated. The reaction Gibbs free energy results also indicate that this is the most favoured site for free radical scavenge.ConclusionThe obtained results show that HAT and SPLET mechanisms are the thermodynamically plausible reaction pathways of free radical scavenge by hydrazone antioxidants. The reactivity of these compounds towards the hydroperoxyl radical (HOO·) was greater than that towards the methyl peroxyl radical (CH3OO·) based on the exergonicity of the calculated reaction Gibbs free energy.Graphical abstract

Comparison of the yields of mono-, Di- and tri-chlorinated HAAs and THMs in chlorination and chloramination based on experimental and quantum-chemical data

Thermodynamic and kinetic aspects of the formation of trihalomethanes and haloacetic acids determined based on the quantum chemical (QC) simulations were compared in this study with the experimental data generated using the differential spectroscopy approach in chlorination and chloramination. The ratios of the slopes of the correlations between -DlnA350 values and individual DBPs concentrations (SNH2Cl/SHOCl) were observed to be linearly correlated with the ratios of the Gibbs free energies (ΔGNH2Cl/ΔGHOCl) of the corresponding reactions of chloramine and chlorine with acetaldehyde which was used as a model DBP precursor in QC simulations. Further QC examination of the kinetics of chlorination and chloramination of the model compound acetoacetic acid showed that the activation energy of reactions between monochloramine that directly participates in substitution reactions to form mono-, di and tri-halogenated intermediates are 2–3 times higher than those of HOCl formed via the hydrolysis monochloramine. This result confirms that the interactions of chloramine with NOM and ensuing DBP formation are primarily mediated by the free chlorine released as a result of the hydrolysis of monochloramine while direct halogenation of NOM by monochloramine is likely to provide a small contribution to DBP formation.

Quantum-mechanical determination of the incorporation of pentavalent plutonium into carbonate and sulfate minerals

Pentavalent plutonium is the most abundant form of soluble, mobile, and oxidized Pu in natural systems. The incorporation of Pu into environmentally abundant mineral hosts can strongly influence the transport and concentration of contaminants in both aqueous environments and the subsurface. This study determines the incorporation energy (ΔE, ΔH, and ΔG) of (PuO2)+(HSO4)− and (PuO2)+(HCO3)− from solid Pu2O5 and aqueous (PuO2)+ as sources of Pu(V), as well as the adsorption with subsequent surface incorporation, in a step-by-step approach onto/into different sulfate and carbonate minerals using ab initio computational methods.Solid source and sink reaction energies are calculated for carbonate and sulfate mineral hosts as(MCO3)4 + ½(Pu2O5) + (H2CO3) ⇌ ½(H2O) + (MCO3)3(PuO2)(HCO3) + (MCO3) for carbonate structures and(MSO4)4 + ½(Pu2O5) + (H2SO4) ⇌ ½(H2O) + (MSO4)3(PuO2)(HSO4) + (MSO4) for sulfate structures, where “M” denotes the metal cation being replaced by PuO2+ (M = Ba, Sr, Pb, Ca).For Pu(V) from solid sources, sulfate group host minerals with the largest cations result in the most favorable incorporation energies; for aqueous sources and sinks, this effect is more than compensated by smaller host cations gaining more hydration energy when released. Thus, incorporation favorability using aqueous sources and sinks vs. solids are nearly reversed, with the smallest cationic radii corresponding to the lowest incorporation energy.While previous studies have used a similar methodology for calculating the thermodynamics of incorporation into bulk minerals, what is new in this study is that the method was extended to observe the rate-controlling steps from a species in solution (e.g., PuO2+ and HSO4− or HCO3−), to their co-adsorbed state on the mineral surface, followed by their co-incorporation (by replacing divalent cations and anions from the surface of the host mineral), and finally being incorporated into the bulk, mimicking the stability of co-precipitated or overgrown plutonyl defects. As the plutonyl ion approaches the surface, a small activation barrier has to be overcome (∼0.2 eV), followed by adsorption which is exothermic (∼–2.6 eV) with potential subsequent surface incorporation (endothermic ∼1.2 eV). Combining these steps results in a surface incorporation of plutonyl that is energetically downhill (∼–1.2 eV), which can sequester plutonyl without the addition of any external energy. Keeping the substituted host ions above the incorporation site is more energetically favorable than releasing them, generating a metastable plutonyl overgrowth site where continued growth is more favorable than re-releasing the plutonyl.These findings, with this more process-oriented and environmentally-relevant approach of surface interactions, considering mineral bulk and surfaces, hydration, and enthalpy, entropy, and Gibbs free energy of individual reaction, facilitate the evaluation of incorporation reactions and narrows the list of minerals favorable for the incorporation of actinides to complement (particularly resource-limited) experimental study. In addition, it may serve as a model for future semi-kinetic studies where a full computational treatment of the kinetics is prohibitively computationally expensive.

Thermodynamically consistent estimation of Gibbs free energy from data: data reconciliation approach.

Thermodynamic analysis of biological reaction networks requires the availability of accurate and consistent values of Gibbs free energies of reaction and formation. These Gibbs energies can be measured directly via the careful design of experiments or can be computed from the curated Gibbs free energy databases. However, the computed Gibbs free energies of reactions and formations do not satisfy the thermodynamic constraints due to the compounding effect of measurement errors in the experimental data. The propagation of these errors can lead to a false prediction of pathway feasibility and uncertainty in the estimation of thermodynamic parameters. This work proposes a data reconciliation framework for thermodynamically consistent estimation of Gibbs free energies of reaction, formation and group contributions from experimental data. In this framework, we formulate constrained optimization problems that reduce measurement errors and their effects on the estimation of Gibbs energies such that the thermodynamic constraints are satisfied. When a subset of Gibbs free energies of formations is unavailable, it is shown that the accuracy of their resulting estimates is better than that of existing empirical prediction methods. Moreover, we also show that the estimation of group contributions can be improved using this approach. Further, we provide guidelines based on this approach for performing systematic experiments to estimate unknown Gibbs formation energies. The MATLAB code for the executing the proposed algorithm is available for free on the GitHub repository: https://github.com/samansalike/DR-thermo. Supplementary data are available at Bioinformatics online.

Consecutive Marcus Electron and Proton Transfer in Heme Peroxidase Compound II-Catalysed Oxidation Revealed by Arrhenius Plots

Electron and proton transfer reactions in enzymes are enigmatic and have attracted a great deal of theoretical, experimental, and practical attention. The oxidoreductases provide model systems for testing theoretical predictions, applying experimental techniques to gain insight into catalytic mechanisms, and creating industrially important bio(electro)conversion processes. Most previous and ongoing research on enzymatic electron transfer has exploited a theoretically and practically sound but limited approach that uses a series of structurally similar (“homologous”) substrates, measures reaction rate constants and Gibbs free energies of reactions, and analyses trends predicted by electron transfer theory. This approach, proposed half a century ago, is based on a hitherto unproved hypothesis that pre-exponential factors of rate constants are similar for homologous substrates. Here, we propose a novel approach to investigating electron and proton transfer catalysed by oxidoreductases. We demonstrate the validity of this new approach for elucidating the kinetics of oxidation of “non-homologous” substrates catalysed by compound II of Coprinopsis cinerea and Armoracia rusticana peroxidases. This study – using the Marcus theory – demonstrates that reactions are not only limited by electron transfer, but a proton is transferred after the electron transfer event and thus both events control the reaction rate of peroxidase-catalysed oxidation of substrates.

DFT Quantum Chemical Studies on Structural, Nonlinear Optical, Reactivity and Thermodynamic Properties of 4‐Methoxy‐2‐{(E)‐[(thiophen‐2‐yl)ethylimino]methyl}phenol

AbstractThe molecular structure of 4‐Methoxy‐2‐{(E)‐[(thiophen‐2‐yl)methylimino]methyl}phenol was optimized using the PBEPBE, B3PW91 and B3LYP methods with the 6–311++G(d,p) basis set and compared to experimental X‐ray data. Density functional computations of the interaction energies, molecular electrostatic potential, and thermodynamic functions have been carried out using the B3LYP method with the 6–311++G(d,p) basis set for the title molecule. The chemical reactivity behaviors of the tautomeric forms of the compound were analyzed at the B3LYP/6‐311++G(d,p) level. Additionally, the solvent effects have been investigated with the integral equation formalism polarizable continuum model. The dipole moment, first hyperpolarizability and linear polarizability values of the tautomeric forms of the compound were computed using the B3LYP/6‐311++G(d,p) method. The changes of the entropy, enthalpy and Gibbs free energy for the formation reaction of the compound have been predicted in different temperature utilizing the statistical thermodynamical technique.

Theoretical study of H-atom abstraction reactions from CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 by NO3 radical & subsequent degradation

The nocturnal reactions of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 initiated by NO3 radicals are important sources of alkyl radicals and nitric acids. In this paper, the thermodynamics and kinetics of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 induced by NO3 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:k1 = 1.13 × 10−40T9.24exp(1675.99/T)k2 = 2.23 × 10−23T2.81exp(-4476.24/T)k3 = 5.63 × 1043T−19.20exp(-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 NO3 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 –OCH2- sites are the main reaction pathways. The thermodynamic and kinetic data of the reaction CH3CH2OCH2CH3, CHF2CF2OCH2CF3 with NO3 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 CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 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 CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 on air quality, as well as its atmospheric lifetime and durability.The atmospheric lifetimes of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 are evaluated in the NO3-concentration range of 5 × 108-2 × 109 molecule cm−3 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 CH3CH2OCHCH3, CF3CHOCF2CHF2 and CF3CHOCH3 are further oxidized into organic nitrates in the presence of O2 and NO. Organic nitrites can be isomerized into organic nitrates or degraded to form CH3C(O•)HOCH2CH3, CF3C(O•)HOCF2CHF2 and CH3C(O•)HOCF3 alkoxy radicals and NO2. This work provides deep insight into the night migration and transformation mechanism of the three ethers.