Reaction of OH radical and ozone with methyl salicylate – a DFT study

A theoretical study on the reaction mechanism of methyl salicylate (MeSA), a green leaf volatile organic compound with OH radical and ozone, has been carried out using density functional theory methods using B3LYP, M06‐2X and MPW1K functionals with 6‐311++G(d,p) basis set. The atmospheric degradation pathways of MeSA with OH radical are studied under two different pathways, viz. H‐atom abstraction and electrophilic addition of OH radical. The hydrogen abstraction from –OH group is found to be the dominant reaction channel with small barrier height. Likewise, the electrophilic addition of OH radicals at the para position of MeSA is found to be favourable rather than the ortho and meta positions because of the small barrier height. However, the reaction of MeSA with respect to the addition of O₃ is initiated only through the cycloaddition to the C?C bond, resulting in primary ozonide. The Arrhenius plot for most of the addition reaction shows positive temperature dependence, while for the abstraction reaction, it exhibits negative temperature dependence over the temperature range of 278–350 K. The calculated theoretical rate constants are in good agreement with available experimental data. Overall, the addition of both OH radical and ozone possesses ability to degrade MeSA, but slower when compared with the Cl radical. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH,and radicals corresponding to loss of H atom

Sulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with ³O₂ to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO?) plus NO₂. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (Δ_fH°, S°, and C_p(T)) of 3 corresponding alcohols HOCH₂SCH₂CH₃, CH₃SCH(OH)CH₃, and CH₃SCH₂CH₂OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (Δ_fH°₂₉₈) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ?_fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.     

Theoretical studies on the hydrogen abstraction reactions of methyl esters with HO2 radical and the following β‐scission reactions

Unsaturated fatty acid methyl esters are ubiquitous in biodiesel fuels. The C = C double bond greatly affects the combustion characteristics of biodiesel, especially its ignition behavior at low temperatures. In this work, we report detailed theoretical study on the mechanism and kinetics of the hydrogen abstraction reactions of linear unsaturated C6 methyl esters with hydroperoxy radical (HO₂), which play a critical role in the low‐temperature combustion of biodiesel. Reaction profiles are obtained via intrinsic reaction coordinate (IRC) analysis including the formation of reactant complexes and product complexes at the entrance and exit channels, respectively. The potential energy surfaces are explored at the CBS‐QB3 level. The following β‐scission reactions of the forming radicals are also investigated at the same level of theory. The high‐pressure limit rate constants for all the reactions in the temperature range from 500 to 2000 K are calculated via conventional transition‐state theory with quantum tunneling effect and fitted to the modified Arrhenius expression.     

DFT study on abstraction reaction mechanism of oh radical with 2‐methoxyphenol

Reaction mechanism of 2‐methoxyphenol (2MP) (guaiacol) with OH radical has been performed using density functional theory methods BH&HLYP and MPW1K method with 6‐311++G(d,p) basis set. Single‐point energy calculations were done using CCSD(T)/6‐311++G(d,p). The theoretical results reveal that the hydrogen abstraction from methoxy group is found to be the dominant reaction channel with an energy barrier of 9.31 kcal/mol. Also, time‐dependent density functional theory calculations have been performed using BH&HLYP/6‐311++G(d,p) level of theory, and the results reveal that the reactions occur in ground state than the excited state. The results of reaction force profile indicate that structural rearrangements are most influential with high percentage than the relaxation process. The calculated theoretical rate constants (12.19 × 10^?11 cm³ molecule^?1 s^?1) are in good agreement with the experimental rate constant. The atmospheric lifetime of 2‐methoxyphenol with respect to OH radicals is 2.27 hours, which implies that OH radical plays an important role in the degradation of 2MP. The Wiberg bond index of the abstraction reaction reveals that the bond order is concerted, partially synchronic. The reactant‐like transition state satisfies Hammond postulate, which eventually results in an exothermic reaction, and the product‐like transition state reveals in endothermic nature.     

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO₂ radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO₂ + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO₂ + FOX-7 results in the formation of NO₃ radical, which has never been detected experimentally during the decomposition of FOX-7.     

DFT study on addition reaction mechanism of guanine‐cytosine base pair with OH radical

The addition reaction mechanism of OH radical with guanine‐cytosine (G^.C) base pair has been explored at the B3LYP/DZP++ level of density functional theory (DFT). Structures perturbations along the hydroxylation of G^.C base pair cause strain in the pairing and double‐strand breaks in DNA. Seven possible hydroxylation reactions are exothermic, and the reaction energy decreases in the order of G^.C^C4 > G^C5.C > G^C2.C > G^C4.C > G^.C^C5 > G^.C^C6 > G^C8.C. The hydroxylation reactions at G^.C^C5 and G^C8.C sites appear to be barrierless, and the sequence of the barrier energy is G^.C^C4 > G^C4.C > G^C2.C > G^C5.C > G^.C^C6 > G^.C^C5 ~ G^C8.C. The results indicate that hydroxylation at G^C8.C, G^.C^C5 and G^.C^C6 are more thermodynamically and kinetically favorable than other sites in G^.C base pair. Considering the solvent effects by using the polarizable continuum model, the stabilities of all the compounds are increased significantly. Little change is taken place on the data of the reaction energies and barrier energies. Their sequences and the stability order follow the same trends like them in gas phase. The fluctuation of natural bond orbital charge further confirms that the hydroxylation reactions are exothermic. And transient spectra computed with the time‐dependent density functional theory (TD‐DFT) match well with the previous experimental and theoretical reports. Our deduced mechanism is in good agreement with the experimentally observed hydroxylated adducts. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanism and kinetics of the atmospheric degradation of 2-formylcinnamaldehyde with O3 and hydroxyl OH radicals – a theoretical study

In the present investigation, the reaction mechanism and kinetics of 2-formylcinnamaldehyde (2-FC) with O₃ and hydroxyl OH radicals were studied. The reaction of 2-FC with O₃ radical are initiated by the formation of primary ozonide, whereas the reaction of 2-FC with the hydroxyl OH radical are initiated by two different ways: (1). H-atom abstraction by hydroxyl OH radical from the –CHO and –CH = CHCHO group of 2-FC (2). Hydroxyl OH addition to the –CH = CHCHO group to the ring-opened 2-FC. These reactions lead to the formation of an alkyl radical. The reaction pathways corresponding to the reactions between 2-FC with O₃ and hydroxyl OH radicals have been analysed using density functionals of B3LYP and M06-2X level of methods with the 6-31+G(d,p) basis set. Single-point energy calculations for the most favourable reactive species are determined by B3LYP/6-311++G(d,p) and CCSD(T)/6-31+G(d,p) levels of theory. From the obtained results, the hydroxyl OH addition at C8 position of 2-FC are most favourable than the C9 position of 2-FC. The subsequent reactions of the alkyl radicals, formed from the hydroxyl OH addition at C8 position, are analysed in detail. The individual and overall rate constant for the most favourable reactions are calculated by canonical variational transition theory with small-curvature tunnelling corrections over the temperature range of 278–350 K. The calculated theoretical rate constants are in good agreement with the available experimental data. The Arrhenius plot of the rate constants with the temperature are fitted and the atmospheric lifetimes of the 2-FC with hydroxyl OH radical reaction in the troposphere calculate for the first time, which can be applied to the study on the atmospheric implications. The condensed Fukui function has been verified for the most favourable reaction sites. This study can be regarded as an attempt to investigate the O₃-initiated and hydroxyl OH-initiated reaction mechanisms of 2-FC in the atmosphere.     

Thermochemistry,bond energies and internal rotor barriers of methyl sulfinic acid,methyl sulfinic acid ester and their radicals

Sulfur–Oxygen containing hydrocarbons are formed in oxidation of sulfides and thiols in the atmosphere, on aerosols and in combustion processes. Understanding their thermochemical properties is important to evaluate their formation and transformation paths. Structures, thermochemical properties, bond energies, and internal rotor potentials of methyl sulfinic acid CH₃S(?O)OH, its methyl ester CH₃S(?O)OCH₃ and radicals corresponding to loss of a hydrogen atom have been studied. Gas phase standard enthalpies of formation and bond energies were calculated using B3LYP/6‐311G (2d, p) individual and CBS‐QB3 composite methods employing work reactions to further improve accuracy of the ${\Delta} _{{\bf f}} H_{{\bf 298}}^{{\bf o}} $ . Molecular structures, vibration frequencies, and internal rotor potentials were calculated. Enthalpies of the parent molecules CH₃S(?O)OH and CH₃S(?O)OCH₃ are evaluated as ?77.4 and ?72.7 kcal mol^?1 at the CBS? QB3 level; Enthalpies of radicals C^?H₂? S(?O)? OH, CH₃? S^?(?O)₂, C^?H₂? S(?O)? OCH₃ and CH₃? S(?O)? OC^?H₂ (CBS‐QB3) are ?25.7, ?52.3, ?22.8, and ?26.8 kcal mol^?1, respectively. The CH₃C(?O)O—H bond dissociation energy is of 77.1 kcal mol^?1. Two of the intermediate radicals are unstable and rapidly dissociate. The CH₃S(?O)? O. radical obtained from the parent CH₃? S(?O)? OH dissociates into methyl radical (${\bf CH}_{{\bf 3}}^{{\bf .}} $ ) plus SO₂ with endothermicity (ΔH_rxn) of only 16.2 kcal mol^?1. The CH₃? S(?O)? OC^?H₂ radical dissociates into CH₃? S^?=O and CH₂=O with little or no barrier and an exothermicity of ?19.9 kcal mol^?1. DFT and the Complete Basis Set‐QB3 enthalpy values are in close agreement; this accord is attributed to use of isodesmic work reactions for the analysis and suggests this combination of B3LYP/work reaction approach is acceptable for larger molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

水辅助下的OH自由基与CH_3OOH气相反应机理的理论研究

利用量子化学计算方法对单个水分子不存在与存在的情况下OH自由基与CH3OOH的气相氢抽取反应进行了理论研究.在BHand HLYP/6-311++G(2df,2pd)理论水平下优化了所有驻点的几何构型,在此基础上利用CCSD(T)/cc-p VTZ方法对所有驻点的单点能重新进行了计算.计算结果表明,OH自由基与CH3OOH反应的主要通道是OH自由基抽取CH3OOH中的-OH基团上的H原子.在单个水分子存在的情况下,反应的主要通道没有改变,但是水化过渡态的能量显著地降低,显然单个水分子对OH+CH3OOH反应具有催化效应.     

水辅助下的OH自由基与CH3OOH气相反应机理的理论研究

利用量子化学计算方法对单个水分子不存在与存在的情况下OH自由基与CH3OOH的气相氢抽取反应进行了理论研究。在BHandHLYP/6-311++G(2df,2pd)理论水平下优化了所有驻点的几何构型,在此基础上利用CCSD(T)/cc-pVTZ方法对所有驻点的单点能重新进行了计算。计算结果表明,OH自由基与CH3OOH反应的主要通道是OH自由基抽取CH3OOH中的-OH基团上的H原子。在单个水分子存在的情况下,反应的主要通道没有改变,但是水化过渡态的能量显著地降低,显然单个水分子对OH+CH3OOH反应具有催化效应。     

DFT study of adenine‐uracil base pair damage by OH radical

The hydrogen abstraction and addition reactions of OH radical with A·U base pair have been explored by using density functional theory (DFT) both in gas phase and in aqueous solution. Solvent effects were taken into consideration by using the polarized continuum model. All the reaction pathways are exothermic in energy, and the compounds in aqueous phase are more favorable than those in gas phase. The relative free energies of adducts in the addition reaction are lower than those obtained for products in hydrogen abstraction reaction. Among dehydrogenation reaction, the hydrogen abstractions from A^C2·U and A^N6·U sites are more favorable than those from A^C8·U, A·U^C5, and A·U^C6 sites. In addition, hydroxylation at A^C8·U, A·U^C5, and A·U^C6 sites are more probable than other investigated positions. The hydroxylation at A^H8·U site is most favorable, and hydroxylation at A·U^C5 site is more preference than that at A·U^C6 site controlled by the kinetics factors. The data in both gas phase and water solution demonstrated that addition of OH radical to A·U^C5 and A·U^C6 sites are more thermodynamically and kinetically favorable than abstracting the hydrogen atom form A·U^C5 and A·U^C6 sites. The phenomena are in agreement with the experimental observations. Copyright © 2015 John Wiley & Sons, Ltd.     

甲基乙烯醚和OH反应机理的理论研究

利用量子化学从头计算的方法对甲基乙烯醚的两个异构体之间的转化,羟基与顺式-甲基乙烯醚和反式-甲基乙烯醚的加成反应,以及羟基提取甲基上的氢原子的反应机理进行了研究.研究结果表明:顺式-甲基乙烯醚比反式-甲基乙烯醚更加稳定,在QCISD/6-31G(d,P)//BHandHLYP/6.311 G(d,P)理论水平下,OH加到顺式-甲基乙烯醚1号住的碳原子上需要跨越的能垒比其它反应通道需要跨越的能垒少7.5～34 KJ/mol,因此是主要的反应通道,而OH加在反式.甲基乙烯醚2号位的碳原子上所需要跨越的能垒比其它反应路径所需要跨越的能垒少8.3～26.7 kJ/mol,因此是主要的反应路径.利用经典过渡态理论计算了总的速率常数     

Time‐resolved resonance Raman and density functional theory study of the photochemistry of 4‐benzoylpyridine in acetonitrile and 2‐propanol

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the intermolecular hydrogen‐abstraction reaction of the triplet state of 4‐benzoylpyridine (4‐BPy) in 2‐propanol solvent is reported. The TR³ results reveal a rapid hydrogen abstraction (<10 ns) by the 4‐BPy triplet state (nπ*) with the 2‐propanol solvent, leading to formation of a 4‐BPy ketyl radical and an associated dimethyl ketyl radical partner from the solvent. The recombination of these two radical species occurs with a time constant about 200 ns to produce a para‐N‐LAT (light absorbing transient). The structure, major spectral features, and identification of the ketyl radical and the para‐N‐LAT coupling complex have been determined and confirmed by comparison of the TR³ results with results from density functional theory (DFT) calculations. A reaction pathway for the photolysis of 4‐BPy in 2‐propanol deduced from the TR³ results is also presented. The electron‐withdrawing effect of the heterocyclic nitrogen for 4‐BPy on the triplet state makes it have a significantly higher chemical reactivity for the hydrogen abstraction with 2‐propanol compared to the previously reported corresponding benzophenone triplet reaction under similar reaction conditions. In addition, the 4‐BPy ketyl radical reacts with the dimethyl ketyl radical to attach at the para‐N atom position of the pyridine ring to form a cross‐coupling product such as 2‐[4‐(hydroxy‐phenyl‐methylene)‐4h‐pyridin‐1‐yl]‐propan‐2‐ol instead of attacking at the para‐C atom position as was observed for the corresponding benzophenone reaction reported in an earlier study. Copyright © 2008 John Wiley & Sons, Ltd.     

DFT studies on the cascade rearrangement reactions of the cubylcarbinyl radical

DFT (U)B3LYP calculations with the 6‐311 + G** basis set were carried out to investigate the mechanisms of cascade rearrangement reactions (involving eight reaction channels) of the cubylcarbinyl radical (radical 1 ). The rate constant for each reaction step was calculated on the basis of the conventional transition state theory. The reaction channel from radical 1 to the 4‐(4‐methylenecyclobut‐2‐enyl) radical is preferred kinetically, while the reaction channel from radical 1 to the 1‐homocubyl radical is unfavorable. The mechanism of the conversion from radical 1 to the tricyclic dienes radical, which is experimentally uncertain, is predicted to be a stepwise process with the methylenesecocubyl radical as an intermediate instead of a concerted reaction. The energy barrier and rate constant of the initial reaction step are evaluated to be 2.8 kcal/mol and 3.0 × 10¹⁰ s^?1, respectively, in excellent agreement with the corresponding experimental values. Copyright © 2010 John Wiley & Sons, Ltd.     

Nature of the transient species formed in the pulse radiolysis of 4‐hydroxybenzyl alcohol in aqueous solutions: observation of equilibrium in the reaction of OH‐adducts with HPO ions

Reactions of ^. OH/O ^.? radicals, H‐atoms as well as specific oxidants such as N and Cl radicals with 4‐hydroxybenzyl alcohol (4‐HBA) in aqueous solutions have been investigated at various pH values using the pulse radiolysis technique. At pH 6.8, ^. OH radicals were found to react with 4‐HBA (k = 6 × 10⁹ dm³ mol^?1 s^?1) mainly by contributing to the phenyl moiety and to a minor extent by H‐abstraction from the ? CH₂OH group. ^. OH radical adduct species of 4‐HBA, i.e., ^. OH‐(4‐HBA) formed in the addition reaction were found to undergo dehydration to give phenoxyl radicals of 4‐HBA. Decay rate of the adduct species was found to vary with pH. At pH 6.8, decay was very much dependent on phosphate buffer ion concentrations. Formation rate of phenoxyl radicals was found to increase with phosphate buffer ion concentration and reached a plateau value of 1.6 × 10⁵ s^?1 at a concentration of 0.04 mol dm^?3 of each buffering ion. It was also seen that ^. OH‐(4‐HBA) adduct species react with HPO ions with a rate constant of 3.7 × 10⁷ dm³ mol^?1 s^?1 and there was no such reaction with H₂PO ions. However, the rate of reaction of ^. OH‐(4‐HBA) adduct species with HPO ions decreased on adding KH₂PO₄ to the solution containing a fixed concentration of Na₂HPO₄ which indicated an equilibrium in the H⁺ removal from ^. OH‐(4‐HBA) adduct species in the presence of phosphate ions. In the acidic region, the ^. OH‐(4‐HBA) adduct species were found to react with H⁺ ions with a rate constant of 2.5 × 10⁷ dm³ mol^?1 s^?1. At pH 1, in the reaction of ^. OH radicals with 4‐HBA (k = 8.8 × 10⁹ dm³ mol^?1 s^?1), the spectrum of the transient species formed was similar to that of phenoxyl radicals formed in the reaction of Cl radicals with 4‐HBA at pH 1 (k = 2.3 × 10⁸ dm³ mol^?1 s^?1) showing that ^. OH radicals quantitatively bring about one electron oxidation of 4‐HBA. Reaction of ^. OH/O ^.? radicals with 4‐HBA by H‐abstraction mechanism at neutral and alkaline pH values gave reducing radicals and the proportion of the same was determined by following the extent of electron transfer to methyl viologen. H‐atom abstraction is the major pathway in the reaction of O ^.? radicals with 4‐HBA compared to the reaction of ^. OH radicals with 4‐HBA. At pH 1, transient species formed in the reactions of H‐atoms with 4‐HBA (k = 2.1 × 10⁹ dm³ mol^?1 s^?1) were found to transfer electrons to methyl viologen quantitatively. Copyright © 2009 John Wiley & Sons, Ltd.     

Atmospheric fate of diketones and OH radical–kinetics,reaction force,ETS-NOCV analysis

In this work, we have focused on the atmospheric reaction chemistry of two α-diketones 2,3-Pentanedione (2,3-PTD) and 2,3-hexanedione (2,3-HEX) with OH radical. The full reaction pathway was studied theoretically under H-atom abstraction reaction using density functional theory and wave-function-based MP2 calculations. Single-point energy calculations were performed at CCSD(T) level of theory with 6–31+G(d,p) basis set. The H-atom abstraction from –CH₂ group is the most dominant channel in both 2,3-PTD and 2,3-HEX with OH radical. The fate of secondary reactions of peroxy and alkoxy radical is studied in detail. The reaction force analysis shows that abstraction process is dominated by structural rearrangement than electronic reordering. The ETS-NOCV-based reaction scheme is studied in order to find out the pair wise interaction energy of the chemical bonding. The ETS-NOCV method for all the transition states shows π-bonding nature for the bond breaking (C–H) and bond formation (O–H) due to the presence of hydrogen bond. The theoretical rate constant value matches well with the experimental rate constant value for both α-diketones. Normal linear Arrhenius behaviour for all the pathways is found in the range of 278–350 K. The short atmospheric lifetime indicates the removal process of diketones with OH radical.     

Radical anions containing the dioxidated 1,2,5‐thiadiazole heterocycle

Radical anions of 3,4‐aryl disubstituted 1,2,5‐thiadiazole 1,1‐dioxide were obtained by chemical and electrochemical reduction of their substrates, and characterized by ESR spectroscopy and cyclic voltammetry. The radical anion of the phenanthro[9,10‐c]‐1,2,5‐thiadiazole 1,1‐dioxide was found to be very stable in an aprotic solvent solution and did not react readily when water was added to the aprotic solvent, or the solution was saturated with oxygen gas. The radical formation chemical reaction competed with nucleophilic addition to the C?N bond of the thiadiazoles. A possible reaction mechanism, and a common reaction intermediate, supported by density functional theory calculations, is presented for the most stable radical. Copyright © 2009 John Wiley & Sons, Ltd.     

Hidden chemistry in phenoxyl radical (C6H5O•) coupling reaction mechanism revealed

A novel hidden reaction of the phenoxyl radical (C₆H₅O^?) with a specific daughter is found to significantly alter its hitherto accepted coupling reactions' scheme. Transient characterizations and mechanistic evaluations in highly acidic to strongly alkaline aqueous medium reveal this concurrent reaction competing favorably in nanosecond–microsecond time‐scale with the five distinct C₆H₅O^? + C₆H₅O^? reactions, which produce various phenolic end‐products as reported earlier (M. Ye and R. H. Schuler, J. Phys. Chem. 1989, 93, 1898). Presently, only the symmetric 4,4′‐dioxo transient precursor, O?C₆H₅? H₅C₆?O that leads to the stable 4,4′‐biphenol product, gets partially oxidized by a fraction of remaining C₆H₅O^?. The resulting secondary transient ^?C₁₂H₉O₂ radical is generated at diffusion‐controlled rate, k > 5.0 × 10⁹ M^?1 s^?1, and follows an independent chemistry. Consequently, when the previously reported five coupled end product distribution ratios were appropriately updated, the respective fractional values revealed a closer match for the symmetric 2,2′‐ and 4,4′‐biphenols with their suggested coupling reaction branching probabilities based on the atomic spin‐density distributions in the C₆H₅O^? radical (P. Neta, R. W. Fessenden, J. Phys. Chem., 1974, 78, 523). Results also suggest that in the remaining fraction, differential solvation in aqueous medium of various orientation‐related encounter complexes (C₆H₅O…C₆H₅O) formed during coupling favors rearrangement only toward 2,4′‐biphenolic product, at the cost of 2‐ and 4‐phenoxyphenolic species. Copyright © 2009 John Wiley & Sons, Ltd.     

Oxidation of substituted triazines by sulfate radical anion (SO) in aqueous medium: a laser flash photolysis and steady state radiolysis study

Laser flash photolysis has been used to determine the bimolecular rate constants and the spectral nature of the intermediates obtained by the reaction of sulfate radical anion (SO) with 1,3,5‐triazine (T), 2,4,6‐trimethoxy‐1,3,5‐triazine (TMT), 2,4‐dioxohexahydro‐1,3,5‐triazine (DHT), and 6‐chloro N‐ethyl N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine (atrazine, AT). The rate constants determined were in the range 4.6 × 10⁷–3 × 10⁹ dm³ mol^?1 s^?1 at pH 6. The transient absorption spectra obtained from the reaction of SO with T, TMT, DHT and AT has an absorption maximum in the region 320–350 nm and was found to undergo second‐order decay. The intermediate species is assigned to N‐yl C(OH) radical of T (TOH^?), carbon centered neutral radical of TMT, an OH‐adduct of AT and an N‐centered radical in the case of DHT. The interpretations on the experimental results obtained from TMT are supported by DFT calculation using Gaussian 03. Steady state radiolysis technique has also been used to investigate the degradation of AT induced by SO. The degradation profile indicated that about 99% of AT has been decomposed after an absorbed gamma‐radiation dose of 7.5 kGy. The degradation yield of AT (expressed as G(‐AT)) was found to be 0.26 µ mol J^?1. The degradation reactions initiated by SO may thus be employed as a potential alternative for ^?OH‐induced degradation of triazines. Copyright © 2007 John Wiley & Sons, Ltd.     

甲基紫精与醇类间的光诱导电子转移及光催化反应的ESR研究

用ESR方法研究了甲基紫精(MV⁺⁺)与甲醇,乙醇及苄醇等之间的光诱导电子转移和光反应过程.结果发现,甲基紫精存在条件下,某些很稳定的醇类也可以发生光催化分解和光催化氧化的反应,甲基紫精在反应过程中起的是催化剂的作用在无氧条件下,MV⁺⁺/C₂H₅OH体系经UV光照10min后即可观察到很强的MV⁺离子基的信号,表明甲基紫精与乙醇分子之间发生了电子转移;当进行较长时间光辐照,则MV⁺离子基逐步消失而生成H原子和碳中心自由基。在通氧条件下进行光照时,则无MV⁺基信号而产生OOH基和碳中心自由基的信号.当体系中有一定量的水存在时,OOH基减弱而产生·OH基,且随着水量的增加,·OOH基的强度更为减弱直至消失,而同时羟基浓度则大大增加.另一个有趣而重要的现象是,对于MV⁺⁺/苄醇体系,在通氧条件下辐照时可给出很强的超氧阴离子基O₂^-的信号,而MV⁺⁺/甲醇体系可产生较弱的O₂^-信号.但是在无氧时甲基紫精的存在进行光辐照甲醇并不发生反应,而苄醇却可被甲基紫精光催化分解产生很强的苄氧基,羟甲基等自由基.本文详细地研究和讨论了甲基紫精与几种醇之间的光诱导电子转移和相应的均相光催化反应过程的机理.