Kinetics of gas‐phase reactions of CH3OCH2CF3, CH3OCH3, CH3OCH2CH3, CH3CH2OCH2CH3, and CHF2CF2OCH2CF3 with NO3 radicals at 298 K

Rate constants for the gas‐phase reactions of CH₃OCH₂CF₃ (k₁), CH₃OCH₃ (k₂), CH₃OCH₂CH₃ (k₃), and CH₃CH₂OCH₂CH₃ (k₄) with NO₃ radicals were determined by means of a relative rate method at 298 K. NO₃ radicals were prepared by thermal decomposition of N₂O₅ in a 700–750 Torr N₂O₅/NO₂/NO₃/air gas mixture in a 1‐m³ temperature‐controlled chamber. The measured rate constants at 298 K were k₁ = (5.3 ± 0.9) × 10^?18, k₂ = (1.07 ± 0.10) × 10^?16, k₃ = (7.81 ± 0.36) × 10^?16, and k₄ = (2.80 ± 0.10) × 10^?15 cm³ molecule^?1 s^?1. Potential energy surfaces for the NO₃ radical reactions were computationally explored, and the rate constants of k₁–k₅ were calculated according to the transition state theory. The calculated values of rate constants k₁–k₄ were in reasonable agreement with the experimentally determined values. The calculated value of k₅ was compared with the estimate (k₅ < 5.3 × 10^?21 cm³ molecule^?1 s^?1) derived from the correlation between the rate constants for reactions with NO₃ radicals (k₁–k₄) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH₃OCH₂CF₃ and CHF₂CF₂OCH₂CF₃ to be 240 and >2.4 × 10⁵ years, respectively, with respect to reaction with NO₃ radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009     

Shock tube investigation of CH3 + CH3OCH3

The title reaction has been investigated in a diaphragmless shock tube by laser schlieren densitometry over the temperature range 1163-1629 K and pressures of 60, 120, and 240 Torr. Methyl radicals were produced by dissociation of 2,3-butanedione in the presence of an excess of dimethyl ether. Rate coefficients for CH(3) + CH(3)OCH(3) were obtained from simulations of the experimental data yielding the following expression which is valid over the range 1100-1700 K: k = (10.19 ± 3.0)T(3.78)?exp((-4878/T)) cm(3) mol(-1)s(-1). The experimental results are in good agreement with estimates by Curran and co-workers [Fischer, S. L.; Dryer, F. L.; Curran, H. J. Int. J. Chem. Kinet.2000, 32 (12), 713-740. Curran, H. J.; Fischer, S. L.; Dryer, F. L. Int. J. Chem. Kinet.2000, 32 (12), 741-759] but about a factor of 2.6 lower than those of Zhao et al. [Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L. Int. J. Chem. Kinet.2008, 40 (1), 1-18].     

Analysis of the intermolecular interactions between CH3OCH3, CF3OCH3, CF3OCF3, and CH2F2, CHF3

The intermolecular interaction energy curves of CH(3)OCH(3)-CH(2)F(2), CF(3)OCH(3)-CH(2)F(2), CF(3)OCF(3)-CH(2)F(2), CH(3)OCH(3)-CHF(3), CF(3)OCH(3)-CHF(3), and CF(3)OCF(3)-CHF(3) complexes were calculated by the MP2 level ab initio molecular orbital method using the 6-311G** basis set augmented with diffuse polarization functions. We investigate the fluorine substitution effects of both methane and dimethyl ether on intermolecular interactions. In addition, orientation dependence of intermolecular interaction energies is also studied with utilizing eight types of orientations. Our analyses demonstrate that partial fluorinations of methane make electrostatic interaction dominant, and consequently enhance attractive interaction at several specific orientations. On the contrary, fluorine substitutions of dimethyl ether substantially decrease the electrostatic interaction between ether and CH(2)F(2) or CHF(3); thus, there is no such characteristic interaction between the C-H of fluorinated methane and ether oxygen of CF(3)OCF(3) as conventional hydrogen bonding, due to reduced polarity of fluorinated ether. The combination of different pairs of the electrostatic interaction is therefore responsible for the intermolecular interaction differences among the complexes investigated herein and also their orientations.     

Stable conformations of CH3CH2OCH2CH2OH: A comparison of theoretical methods

This article presents the results of an extensive examination of the stable conformations of CH₃CH₂OCH₂CH₂OH at various levels of theory. In particular, 41 initial conformations are optimized using the MM2 force field in BIGSTRN-3; the MINDO/3, MNDO, and AM1 Hamiltonians in AMPAC 2.2; the PM3 Hamiltonian in MOPAC 7.0; and at the HF/STO-3G and HF/3-21G levels using Gaussian 92. The optimized HF/3-21G structures are reoptimized at the HF/6-31G(d) level, and the unique structures are optimized again at the MP2 = FULL/6-31G(d) level. In addition, single-point MP2/6-31G(d) calculations are performed using the HF/6-31G(d) geometries. The goal is to determine the relative accuracy of each method and discuss their strengths and weaknesses. © 1994 by John Wiley & Sons, Inc.     

Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals,the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

The rate constant for the reaction of CH₃OCH₂ radicals with O₂ (reaction (1)) and the self reaction of CH₃OCH₂ radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k₁ was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# → CH₂OCH₂O₂H^# → 2HCHO + OH (k_prod) CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# + M → CH₃OCH₂O₂ + M (k_RO2) k = k_RO2 + k_prod, where k_RO2 is the rate constant for peroxy radical production and k_prod is the rate constant for formaldehyde production. The k₁ values obtained at 296K together with the available literature values for k₁ determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: k_RO2,0 = (9.4 ± 4.2) × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k_RO2,∞ = (1.14 ± 0.04) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_prod,0 = (6.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, where k_RO2,0 and k_RO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH₃OCH₂O₂ radicals and k_prod,0 represents the bimolecular rate constant for the reaction of CH₃OCH₂ radicals with O₂ to yield formaldehyde in the limit of low pressure. k_RO2,∞ = (1.07 ± 0.08) × 10⁻¹¹ exp(−(46 ± 27)/T) cm³ molecule⁻¹ s⁻¹ was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k₅ = (4.1 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and at 18 bar total pressure over the temperature range 296–523K, k₅ = (4.7 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. As a part of this study the decay rate of CH₃OCH₂ radicals was used to study the thermal decomposition of CH₃OCH₂ radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH₃OCH₂ radicals were consistent with the literature value of k₂ = 1.6 × 10¹³exp(−12800/T)s⁻¹. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.     

Theoretical structure and vibrational analysis of ethyl methanesulfonate, CH3SO2OCH2CH3

Ethyl methanesulfonate, CH3SO2OCH2CH3, is well-known as an alkylating agent in mutagenic and carcinogenic processes. Its electronic structure and that of the methanesulfonate anion (CH3SO3-) were determined using optimization methods based on density functional theory and Moller-Plesset second-order perturbation theory. For CH3SO2OCH2CH3, two conformations with symmetries C(s) and C1 are obtained, the former being more stable than the latter. Natural bond orbital (NBO) calculations show the C(s) conformation provides a more favorable geometry of the lone pairs of the oxygen atom linking the ethyl group. The NBO technique also reveals the characteristics of the methanesulfonate anion as a leaving group due to the rearrangement of the excess electronic charge after alkylation. Furthermore, the infrared spectra of CH3SO2OCH2CH3 are reported for the liquid and solid states as well as the Raman spectrum of the liquid. Comparison to experiment of the conformationally averaged IR spectrum of C(s) and C1 provides evidence of the predicted conformations in the solid IR spectrum. These experimental data along with the calculated theoretical force constants are used to define a scaled quantum mechanical force field for the target molecule, which allowed the measured frequencies to be reproduced with a final root-mean-square deviation of 9 cm(-1) and, thus, a reliable assignment of the vibrational spectrum.     

Synthesis and characterization of ferrocenylalkoxygermatranes and crystal structures of FcCH2OGe (OCH2CH2)3N and FcCH(CH3)OGe(OCH2CH2)3N1

Germatranes bearing a ferrocenylalkoxyl moiety have been obtained by the reaction of HOGe(OCH₂CH₂)₃N with various ferrocenyl alcohols. A convenient new synthesis method of FcCH₂OGe(OCH₂CH₂)₃N was reported. FcCH₂OGe(OCH₂CH₂)₃N was prepared in 93% yield when FcCH₂OH reacted with HOGe(OCH₂CH₂)₃N in chloroform at room temperature in the presence of molecular sieves (3 Å) as a dehydrating agent. All compounds were characterized by elemental analysis, ¹H NMR and IR spectroscopy. The molecular structures of FcCH₂OGe(OCH₂CH₂)₃N and FcCH(CH₃)OGe(OCH₂CH₂)₃N have been determined by X‐ray diffraction. The antitumor activities of FcCH₂OGe(OCH₂CH₂)₃N and p‐FcC₆H₄CH₂OGe(OCH₂CH₂)₃N were determined. Copyright © 2005 John Wiley & Sons, Ltd.     

Infrared spectrum of the CH3OCH2 radical in solid argon

The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 ? shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.     

CH3OCF2CF2OCH3+Cl的反应机理及动力学性质

利用密度泛函理论直接动力学方法研究了反应CH₃OCF₂CF₂OCH₃+Cl的微观机理和动力学性质. 在BB1K/6-31+G(d,p)水平上获得了反应的势能面信息, 计算中考虑了反应物CH₃OCF₂CF₂OCH₃两个稳定构象(SC1和SC2)的氢提取通道和取代反应通道. 利用改进的正则变分过渡态理论结合小曲率隧道效应(ICVT/SCT)计算了各氢提取通道的速率常数, 进而根据Boltzmann配分函数得到总包反应速率常数(k_T)以及每个构象对总反应的贡献. 结果表明296 K温度下计算的k_T(ICVT/SCT)值与已有实验值符合得很好. 由于缺乏其他温度速率常数的实验数据, 我们预测了该反应在200-2000 K温度区间内反应速率常数的三参数表达式: k_T=0.40×10^-14T^1.05exp(-206.16/T).     

Synthesis and spectroscopy of N3P3X5OCH=CH2 (X = Cl, F, OCH3, OCH2CF3, N(CH3)2) and N3P3X4(OCH=CH2)2 (X = Cl, N(CH3)2). Correlations of ultraviolet photoelectron spectroscopy and nuclear magnetic resonance data to electronic and geometrical structure

The syntheses of the vinyloxycyclotriphosphazene derivatives N3P3X5OCH=CH2 (X = OMe, OCH2CF3) and the N3P3(NMe2)4(OCH=CH2)2 isomeric mixture along with improved preparations of N3P3X5OCH=CH2 (X = F, NMe2) are reported. The interactions between the vinyloxy function and the cyclophosphazene in these and the previously reported N3P3Cl5 (OCH=CH2) and N3P3F6-n(OCH=CH2)n (n = 1-4) have been examined by ultraviolet photoelectron spectroscopy (UPS) and NMR spectroscopy. The UPS data for the chloro and fluoro derivatives show a strong electron-withdrawing effect of the phosphazene on the olefin that is mediated with decreasing halogen substitution. The 1H and 13C NMR data for N3P3X5OCH=CH2 (X = F, Cl, OMe, OCH2CF3, NMe2) show significant changes as a function of the phosphazene substituent. There is a linear correlation between the beta-carbon chemical shift on the vinyloxy unit and the phosphorus chemical shift at the vinyloxyphosphorus centers. The chemical shifts of the different phosphorus centers on each ring are also related in a linear fashion. These relationships may be understood in terms of the relative electron donor-acceptor abilities of the substituents on the phosphazene ring. The 1H NMR spectra of the N3P3(NMe2)4(OCH-CH2)2 isomeric mixture allow for assignment of the relative amounts of cis and trans isomers. A model for the observed cis preference in the formation of N3P3Cl4(OCH=CH)2 is presented.     

Methoxymethyl cation [CH3OCH2]+ revisited: Experimental and theoretical study

The metastable dissociation of the methoxymethyl cation and a number of its deuterium and ¹³C variants was examined using a reverse-geometry double-focusing mass spectrometer. The loss of methane from the methoxymethyl cation clearly showed a composite peak shape which, when deconvoluted, revealed a bimodal kinetic energy release distribution in the resulting formyl cations. Labelling experiments revealed that the two carbon atoms and all hydrogens become equivalent on the time-scale of the unimolecular dissociation lifetime of the decomposing ion. A small deuterium isotope effect was found which can be rationalized on the basis of zero point energy effects. The bimodal kinetic energy release distribution was shown, with the aid of a four-sector instrument, to be due to the production of both formyl cation (with a large kinetic energy release) and isoformyl cation (with a much smaller kinetic energy release). The methoxymethyl cation was also prepared with a precisely defined amount of internal energy in a Fourier transform ion cyclotron resonance (FTICR) spectrometer by the reaction of methyl cation with formaldehyde. Experiments with ¹³C and deuterium labelling revealed that the dissociation to formyl cation of the methoxymethyl cations formed in the low-pressure FTICR cell by reaction of methyl cation with formaldehyde is accompanied by complete scrambling of the carbons and incomplete scrambling of the hydrogens. Ab initio calculations were carried out which identified and characterized each of the stable minima and transition states for the appropriate reactions. The calculations were fully consistent with the mechanism deduced on the basis of the experimental data.     

Kernresonanzspektroskopische Untersuchungen an cis-(CH3)2Pt[P(OCH3)3]2

100 MHz ¹ H n.m.r. spectra of cis-(CH₃)₂Pt[P(OCH₃)₃]₂ are analysed in full detail as superimposing [AR₃X₉]₂ and [AR₃X₉]₂M systems. The cis structure is derived from J(PP) and J(PtP).     

Atmospheric Chemistry of CH3CH2OCH3: Kinetics and Mechanism of Reactions with Cl Atoms and OH Radicals

The atmospheric chemistry of methyl ethyl ether, CH₃CH₂OCH₃, was examined using FT‐IR/relative‐rate methods. Hydroxyl radical and chlorine atom rate coefficients of k (CH₃CH₂OCH₃+OH) = (7.53 ± 2.86) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k (CH₃CH₂OCH₃+Cl) = (2.35 ± 0.43) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ were determined (297 ± 2 K). The Cl rate coefficient determined here is 30% lower than the previous literature value. The atmospheric lifetime for CH₃CH₂OCH₃ is approximately 2 days. The chlorine atom–initiated oxidation of CH₃CH₂OCH₃ gives CH₃C(O)H (9 ± 2%), CH₃CH₂OC(O)H (29 ± 7%), CH₃OC(O)H (19 ± 7%), and CH₃C(O)OCH₃ (17 ± 7%). The IR absorption cross section for CH₃CH₂OCH₃ is (7.97 ± 0.40) × 10⁻¹⁷ cm molecule⁻¹ (1000–3100 cm⁻¹). CH₃CH₂OCH₃ has a negligible impact on the radiative forcing of climate.     

Atmospheric chemistry of C2F5CH2OCH3 (HFE-365mcf)

FTIR smog chamber techniques were used to measure k(Cl + C(2)F(5)CH(2)OCH(3)) = (2.52 ± 0.37) × 10(-11) and k(OH + C(2)F(5)CH(2)OCH(3)) = (5.78 ± 1.02) × 10(-13) cm(3) molecule(-1) s(-1) in 700 Torr of air diluent at 296 ± 1 K. The atmospheric lifetime of C(2)F(5)CH(2)OCH(3) is estimated to be 20 days. Reaction of chlorine atoms with C(2)F(5)CH(2)OCH(3) proceeds 18 ± 2% at the -CH(2)- group and 82 ± 2% at the -CH(3) group. Reaction of OH radicals with C(2)F(5)CH(2)OCH(3) proceeds 44 ± 5% at the -CH(2)- group and 56 ± 5% at the -CH(3) group. The atmospheric fate of C(2)F(5)CH(2)OCH(2)O radicals is reaction with O(2) to give C(2)F(5)CH(2)OCHO. The atmospheric fate of C(2)F(5)CH(O)OCH(3) radicals is C-C bond-cleavage to give C(2)F(5) radicals and CH(3)OCHO (methyl formate). The infrared spectrum was recorded and used to estimate a global warming potential of 6 (100 year time horizon) for C(2)F(5)CH(2)OCH(3).     

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CH2OCHF2 (HFE-245fa2; HFE-245mf) with the OH radicals and Cl atoms. Two hydrogen abstraction channels and two displacement processes are found for each reaction. For further study, the reaction mechanisms of its products (CF3CH2OCF2 and CF3CHOCHF2) and parent ether CH3CH2OCH3 with OH radical are investigated theoretically. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the B3LYP/6-311G(d,p) level. The energetic information along the MEPs is further refined at the G3(MP2) level of theory. For reactions CF3CH2OCHF2 + OH/Cl, the calculation indicates that the hydrogen abstraction from --CH2-- group is the dominant reaction channel, and the displacement processes may be negligible because of the high barriers. The standard enthalpies of formation for the reactant CF3CH2OCHF2, and two products CF3CH2OCHF2 and CF3CHOCHF2 are evaluated via group-balanced isodesmic reactions. The rate constants of reactions CF3CH2OCHF2 + OH/Cl and CH3CH2OCH3 + OH are estimated by using the variational transition state theory over a wide range of temperature (200-2000 K). The agreement between the theoretical and experimental rate constants is good in the measured temperature range. From the comparison between the rate constants of the reactions CF3CH2OCHF2 and CH3CH2OCH3 with OH, it is shown that the fluorine substitution decreases the reactivity of the C--H bond.