Kinetics Investigation of Reaction of Naphthalene with OH Radicals at 1–3 Torr and 240–340 K

The combination of relative rate method with discharge flow and mass spectrometry (RR/DF/MS) technique was employed to determine the rate constant for the gas‐phase reaction of hydroxyl radicals (OH) with naphthalene at 240?340 K and a total pressure of 1–3 Torr. At 298 K, the rate constant was measured to be cm³ molecule^?1 s^?1, which is in good agreement with reported literature values determined using different techniques. The reaction of OH with naphthalene was found to be essentially independent of pressure in a range of 1?3 Torr at both 298 and 340 K. At 240–340 K, the rate constant of this reaction was found to be negatively dependent on temperature, with an Arrhenius expression of k₁(T) cm³ molecule^?1 s^?1 and k₁(T) cm³ molecule^?1 s^?1 using 1,4‐dioxane and styrene as the reference compounds, respectively. The atmospheric lifetime of naphthalene was estimated to be 9.6 h using the rate constant of naphthalene + OH determined at 277 K in the present work.     

Measurements of the kinetics of the OH + α‐pinene and OH + β‐pinene reactions at low pressure

The rate constants for the OH + α‐pinene and OH + β‐pinene reactions have been measured in 5 Torr of He using discharge‐flow systems coupled with resonance fluorescence and laser‐induced fluorescence detection of the OH radical. At room temperature, the measured effective bimolecular rate constant for the OH + α‐pinene reaction was (6.08 ± 0.24) × 10^?11 cm³ molecule^?1 s^?1. These results are in excellent agreement with previous absolute measurements of this rate constant, but are approximately 13% greater than the value currently recommended for atmospheric modeling. The measured effective bimolecular rate constant for the OH + β‐pinene reaction at room temperature was (7.72 ± 0.44) × 10^?11 cm³ molecule^?1 s^?1, in excellent agreement with previous measurements and current recommendations. Above 300 K, the effective bimolecular rate constants for these reactions display a negative temperature dependence suggesting that OH addition dominates the reaction mechanisms under these conditions. This negative temperature dependence is larger than that observed at higher pressures. The measured rate constants for the OH + α‐pinene and OH + β‐pinene reactions are in good agreement with established reactivity trends relating the rate constant for OH + alkene reactions with the ionization potential of the alkene when ab initio calculated energies for the highest occupied molecular orbital are used as surrogates for the ionization potentials for α‐ and β‐pinene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 300–308, 2002     

Mechanism and Kinetics for the Reaction of NCS and OH Radicals

The mechanism and dynamical properties for the reaction of NCS and OH radicals have been investigated theoretically. The minimum energy paths (MEP) of the reaction were calculated using the density functional theory(DFT) at the B3LYP/6-311 G^** level, and the energies along the MEP were further refined at the QCISD(T)/6-311 G^** level. As a result, the reaction mechanism of the title reaction involves three channels, producing HCS NO and HNC SO products, respectively. Path Ⅰ and path Ⅱ are competitive, with some advantages for path Ⅰ in kinetics. As for path Ⅲ, it looks difficult to react for its high energy barrier. Moreover, the rate constant have been calculated over the temperature range of 8190-2500K using canonical variational transition-state theory (CVT). It was found that the rate constants for both path Ⅰ and path Ⅱ are negatively dependent on temperature, which is similarwith the experimental results for reactions of NCS with NO and NO2, and the variational effect for the rate constant calculation olavs an important role in whole temperature range.     

硝酸异丙酯与Cl原子、OH和NO3自由基反应的机理及动力学

采用CCSD(T)//M06-2X/6-311++G(d,p)方法, 结合传统过渡态理论, 研究了硝酸异丙酯与Cl原子、 OH及NO₃自由基的反应机理和动力学. 两个反应物单体首先形成氢键复合物, 随后X(X=Cl原子、 OH和NO₃自由基)提取硝酸异丙酯中叔碳的α-H原子或甲基的β-H原子, 室温下, 以X提取α-H原子为主. 反应的主要历程为 Cl原子(OH或NO₃自由基)提取(CH₃)₂CHONO₂的α-H原子, 生成HCl(H₂O或HNO₃)分子和(CH₃)₂CONO₂自由基, 后者分解为丙酮和NO₂. 结果表明, 在200~500 K温度范围内, 随着温度的升高, 丙酮和NO₂的产率降低; 在室温下, 硝酸异丙酯与Cl原子、 OH和NO₃自由基反应的速率常数分别为3.933×10^-11, 1.182×10^-13和7.134×10^-19 cm³·molecule^-1·s^-1. 计算所得硝酸异丙酯与OH自由基反应的动力学数据与实验结论一致.     

Interception of Cobalt‐Based Carbene Radicals with α‐Aminoalkyl Radicals: A Tandem Reaction for the Construction of β‐Ester‐γ‐amino Ketones

The interception of cobalt‐based carbene radicals with α‐aminoalkyl radicals was combined with the Kornblum–DeLaMare reaction and provides β‐ester‐γ‐amino ketones, which are otherwise difficult to obtain in high chemoselectivity. Mechanistically, this transformation is an interplay of cobalt‐based carbene radicals, organoradicals, and ionic intermediates and involves the construction of two C? C bonds and one C?O bond in a one‐pot process. The reaction also features a wide substrate scope and is highly efficient and insensitive to moisture and air.     

Experimental Study of the Reaction of Isopropyl Nitrate with OH Radicals: Kinetics and Products

The kinetics of the reaction of isopropyl nitrate (IPN) with OH radicals has been studied using a low‐pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + (CH₃)₂CHONO₂ → products (2). The rate constant of the title reaction was determined using both the absolute method, monitoring the kinetics of OH radicals consumption in excess of IPN, and the relative rate method using the reaction of OH with Br₂ as reference one and following HOBr formation. As a result of the absolute and relative measurements, the overall rate coefficients, k₂ = (6.6 ± 1.2) × 10^?13 exp(–(233 ± 56)/) was determined at a pressure of 1 Torr of helium over the temperature range 268–355 K. Acetone, resulting from H‐atom abstraction from the tertiary C–H bond of IPN followed by 2‐nitroxy‐2‐propyl radical decomposition, was found to be a major reaction product with the yield of 0.82 ± 0.13, independent of temperature in the range 277–355 K.     

Atmospheric Chemistry of α‐Diketones: Kinetics of C5 and C6 Compounds with Cl Atoms and OH Radicals

Carbonyls play an important role in atmospheric chemistry due to their formation in the photooxidation of biogenic and anthropogenic volatile organic compounds and their high atmospheric reactivity. The Cl‐initiated kinetics of two α‐diketones (2,3‐pentanedione (PTD) and 2,3‐hexanedione (HEX)) have been determined as well as the OH + HEX rate constant using atmospheric simulation chamber experiments and the relative rate method. Up to three different reference compounds were used to assess robust results. The following rate constants (in cm³ molecule⁻¹ s⁻¹) have been obtained at 298 K: k (Cl + PTD) = (1.6 ± 0.2) × 10⁻¹¹, k (Cl + HEX) = (8.8 ± 0.4) × 10⁻¹¹, and k (OH + HEX) = (3.6 ± 0.7) × 10⁻¹² with a global uncertainty of 30%. The present determinations of Cl‐ and OH‐ reaction rate constants for HEX constitute first measurements. Using the present measurements, a recently improved structure–activity relationship for Cl + ketone reactions has been updated by introducing an F (–COCO–) factor of 8.33 × 10⁻⁴. Atmospheric lifetime calculations indicate that chlorine‐initiated oxidation may be a significant α‐diketone sink in the marine‐boundary layer or in places where high Cl concentrations may be found.     

Kinetics and Products of the Reactions of Ethyl and n‐Propyl Nitrates with OH Radicals

The kinetics of the reactions of ethyl (1) and n‐propyl (2) nitrates with OH radicals has been studied using a low‐pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo–first‐order conditions from kinetics of OH consumption in high excess of nitrates. The overall rate constants, k₁ = 1.14 × 10^?13 (T/298)^2.45 exp(193/T) and k₂ = 3.00 × 10^?13 (T/298)^2.50 exp(205/T) cm³ molecule^?1 s^?1 (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium over the temperature range (248–500) and (263–500) K, respectively. The yields of the carbonyl compounds, acetaldehyde and propanal, resulting from the abstraction by OH of an α‐hydrogen atom in ethyl and n‐propyl nitrates, followed by α‐substituted alkyl radical decomposition, were determined at T = 300 K to be 0.77 ± 0.12 and 0.22 ± 0.04, respectively.     

CF_2ClC(O)OCH_2CH_3+OH的反应机理及动力学性质的理论研究

利用双水平直接动力学方法,在MCG3-MPWB//M06-2X/aug-cc-pVDZ水平上研究了CF_2ClC(0)OCH_2CH_3+OH的微观反应机理.得到了反应物CF_2ClC(O)OCH_2CH_3的5种稳定构象(RCl~RC5),并对每一构象考察了发生在-CH_3-和-CH_2-基团上的所有可能氢提取反应通道.利用改进的变分过渡态理论(ICVT)结合小曲率隧道效应校正(SCT)计算了各反应通道的速率常数,分析了各构象反应位点选择性.结果表明,对于构象RCl和RC2,低温时氢提取反应主要发生在-CH_2-基团上;而对于构象RC3RC4和RC5,发生在-CH_3基团上的氢提取反应通道在整个温度区间内占绝对优势.根据Boltzmann配分函数计算总包反应速率常数,在298 K温度下计算的体系总包反应速率常数与实验值相符,进而给出200~1000 K温度范围内拟合了速率常数的三参数Arrhenius表达式:k_(overall)=5.45×10~(25)T~(4.54)exp(-685/T).     

Transition from π Radicals to σ Radicals: Substituent‐Tuned Cyclization of Hydrazonyl Radicals

Hydrazonyl radicals are known for their π‐electronic structures; however, their σ‐electronic structures have not been reported as yet. Herein, we show that readily accessible β,γ‐ and γ,δ‐unsaturated N‐trichloroacetyl and N‐trifluoroacetyl hydrazones can be conveniently converted into hydrazonyl σ radicals, which subsequently undergo 5‐exo‐trig radical cyclization at the N¹ or N² atom to form pyrazolines and azomethine imines, respectively.     

Gas‐Phase Reaction of Monomethylhydrazine with Ozone: Kinetics and OH Radical Formation

The gas‐phase reaction of monomethylhydrazine (CH₃NH? NH₂; MMH) with ozone was investigated in a flow tube at atmospheric pressure and a temperature of 295 ± 2 K using N₂/O₂ mixtures (3–30 vol% O₂) as the carrier gas. Proton transfer reaction–mass spectrometry (PTR‐MS) and long‐path FT‐IR spectroscopy served as the main analytical techniques. The kinetics of the title reaction was investigated with a relative rate technique yielding k_MMH+O3 = (4.3 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1. Methyldiazene (CH₃N?NH; MeDia) has been identified as the main product in this reaction system as a result of PTR‐MS analysis. The reactivity of MeDia toward ozone was estimated relative to the reaction of MMH with ozone resulting in k_MeDia+O3 = (2.7 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1. OH radicals were followed indirectly by phenol formation from the reaction of OH radicals with benzene. Increasing OH radical yields with increasing MMH conversion have been observed pointing to the importance of secondary processes for OH radical generation. Generally, the detected OH radical yields were definitely smaller than thought so far. The results of this study do not support the mechanism of OH radical formation from the reaction of MMH with ozone as proposed in the literature.     

Criegee中间体CH_3CHOO与OH自由基反应机理的理论研究

采用CCSD(T)//B3LYP/6-311+G(d,p)方法研究了Criegee中间体CH_3CHOO与OH自由基反应的微观机理.结果表明,上述反应存在抽氢、加成-分解和氧化3类反应通道,其中,syn-CH3CHOO+OH以抽β-H为优势通道,表观活化能为-4.88 k J/mol;anti-CH_3CHOO+OH则以加成-分解反应为优势通道,表观活化能为-13.25 k J/mol.在加成-分解和氧化反应通道中,anti-构象的能垒均低于syn-构象,而抽氢反应则是syn-(β-H)的能垒低于anti-构象.速率常数计算表明,anti-构象的加成-分解反应通道具有显著的负温度效应;syn-和anti-构象的氧化通道具有显著的正温度效应.3类反应具有显著不同的温度效应,说明通过改变温度可显著调节3类反应的相对速率.     

Visible‐Light‐Driven N‐Heterocyclic Carbene Catalyzed γ‐ and ϵ‐Alkylation with Alkyl Radicals

The merging of photoredox catalysis and N‐heterocyclic carbene (NHC) catalysis for γ‐ and ?‐alkylation of enals with alkyl radicals was developed. The alkylation reaction of γ‐oxidized enals with alkyl halides worked well for the synthesis γ‐multisubstituted‐α,β‐unsaturated esters, including those with challenging vicinal all‐carbon quaternary centers. The synthesis of ?‐multisubstituted‐α,β‐γ,δ‐diunsaturated esters by an unprecedented NHC‐catalyzed ?‐functionalization was also established.     

Kinetics of the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one under simulated atmospheric conditions

Relative rate coefficients for the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one have been determined at 298 K and atmospheric pressure by the relative rate technique. OH radicals were generated by the photolysis of methyl nitrite in synthetic air mixtures containing ppm levels of nitric oxide together with the test and reference substrates. The concentrations of the test and reference substrates were followed by gas chromatography. Based on the value k(OH + cyclohexene) = (6.77 ± 1.35) × 10^?11 cm³ molecule^?1 s^?1, rate coefficients for k(OH + 3‐methyl‐2‐cyclohexen‐1‐one) = (3.1 ± 1.0) × 10^?11 and k(OH + 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one) = (2.4 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1 were determined. To test the system we also measured k(OH + isoprene) = (1.11 ± 0.23) × 10^?10 cm³ molecule^?1 s^?1, relative to the value k(OH + (E)‐2‐butene) = (6.4 ± 1.28) × 10^?11 cm³ molecule^?1 s^?1. The results are discussed in terms of structure–activity relationships, and the reactivities of cyclic ketones formed in the photo‐oxidation of monoterpene are estimated. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 7–11, 2002     

Reactivity of 3‐Methylbenzenediazonium Ions with Gallic Acid. Kinetics and Mechanism of the Reaction

We investigated the kinetics and mechanism of the reaction between the 3‐methylbenzenediazonium ions (3MBD), and gallic acids (=3,4,5‐trihydroxybenzoic acid; GA) in aqueous buffer solution under acidic conditions by employing spectrometric, electrochemical, and chromatographic techniques and computational methods. To discern which of the three OH groups of GA is the first one undergoing deprotonation, the geometries of the resulting dianions were optimized by using B3LYP hybrid density‐functional theory (DFT) and a 6‐31G(++d,p) basis set, and the results suggest that the OH group at the 4‐position is the first one which is deprotonated. The variation of the observed rate constant, k_obs, with the acidity at a given [GA] follows an upward curve suggesting that the reaction takes place with the dianionic form of gallic acid, GA^2?, and rate enhancements of ca. 23000 fold are obtained on going from pH 3.5 up to pH 7.5. At relatively high acidities, the variation of k_obs with [GA] is linear with an intercept very close to the value for the thermal decomposition of 3MBD; however, a decrease in the acidity leads to saturation‐kinetics profiles with nonzero, pH‐dependent intercepts. The saturation‐kinetics patterns found suggest the formation of an intermediate in a rapid pre‐equilibrium step, but the nonzero, pH‐dependent intercepts cause the double reciprocal plots of 1/k_obs vs. 1/[GA] to curve. This prompts us to propose an alternative reaction mechanism comprising consecutive equilibrium processes involving the bimolecular, reversible formation of a highly unstable (Z)‐diazo ether which undergoes isomerization to the (E)‐isomer through a unimolecular step. The results obtained indicate the complexity of reactions of arenediazonium ions with nucleophilic arenes containing three or more OH groups.     

Kinetics of the gas‐phase reaction of CF3OC(O)H with OH radicals at 242–328 K

The rate constants, k₁, of the reaction of CF₃OC(O)H with OH radicals were measured by using a Fourier transform infrared spectroscopic technique in an 11.5‐dm³ reaction chamber at 242–328 K. OH radicals were produced by UV photolysis of an O₃–H₂O–He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during UV irradiation. With CF₃OCH₃ as a reference compound, k₁ at 298 K was (1.65 ± 0.13) × 10^?14 cm³ molecule^?1 s^?1. The temperature dependence of k₁ was determined as (2.33 ± 0.42) × 10^?12 exp[?(1480 ± 60)/T] cm³ molecule^?1 s^?1; possible systematic uncertainty could add an additional 20% to the k₁ values. The atmospheric lifetime of CF₃OC(O)H with respect to reaction with OH radicals was calculated to be 3.6 years. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 337–344 2004     

Low C24‐OH and C22‐OH sulfatides in human renal cell carcinoma

Histopathologic diagnosis of renal cell carcinoma (RCC) may sometimes be difficult with small biopsy samples. We applied histology‐directed matrix‐assisted laser desorption/ionization mass spectrometry to RCC samples to evaluate whether and how lipid profiles are different between RCC and normal tissue. We evaluated 59 RCC samples and 24 adjacent normal tissue samples collected from patients who underwent surgery. Five peaks were significantly differently expressed (p < 10^?7) between RCCs and adjacent normal tissue samples. C24‐OH sulfatide (ST‐OH {18:1/24:0}[M‐H]^?; m/z 906.7 in the negative ion mode) and C22‐OH sulfatide (ST‐OH {18:1/22:0}[M‐H]^?; m/z 878.6 in the negative ion mode) were most significantly underexpressed in RCC samples, compared with adjacent normal tissue samples. With 100 random training‐to‐test partitions within these samples, the median prediction accuracy (RCC vs. normal) ranged from 96.3% to 100% at p cutoff values for feature selection ranging from 0.001 to 10^?7. Two oncocytoma samples were predicted as normal tissue by five lipids that were differentially expressed between RCC and normal tissue at p < 10^?7. Clear‐cell, papillary, and chromophobe RCCs were different in lipid profiles. Permutation p‐ values for 0.632+ bootstrap cross‐validated misclassification rates were less than 0.05 for all the classifiers. Thus, lipid profiles differentiate RCC from normal tissue and may possibly classify the histology of RCC. © 2014 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd.