Thermal decomposition of di-t-butyl peroxide in the presence of (CH3)2CCH2: Reactions of CH3, (CH3)2ĊCH2CH3, and (CH3)2ĊCH2C(CH3)2CH2CH3 radicals

A study of the reaction initiated by the thermal decomposition of di-t-butyl peroxide (DTBP) in the presence of (CH₃)₂C?CH₂ (B) at 391–444 K has yielded kinetic data on a number of reactions involving CH₃ (M·), (CH₃)₂CCH₂CH₃ (MB·) and (CH₃)₂?CH₂C(CH₃)₂CH₂CH₃ (MBB·) radicals. The cross-combination ratio for M· and MB· radicals, rate constants for the addition to B of M· and MB· radicals relative to those for their recombination reactions, and rate constants for the decomposition of DTBP, have been determined. The values are, respectively, where θ = RT ln 10 and the units are dm^3/2 mol^?1/2 s^?1/2 for k₂/k and k₉/k, s^?1 for k₀, and kJ mol^?1 for E. Various disproportionation-combination ratios involving M·, MB·, and MBB· radicals have been evaluated. The values obtained are: Δ₁(M·, MB·) = 0.79 ± 0.35, Δ₁(MB·, MB·) = 3.0 ± 1.0, Δ₁(MBB·, MB·) = 0.7 ± 0.4, Δ₁(M·, MBB·) = 4.1 ± 1.0, Δ₁(MB·, MBB·) = 6.2 ± 1.4, and Δ₁(MBB·, MBB·) = 3.9 ± 2.3, where Δ₁ refers to H-abstraction from the CH₃ group adjacent to the center of the second radical, yielding a 1-olefin. © 1994 John Wiley & Sons, Inc.     

The formation of the stable radicals .CH2CN, CH3.CHCN and .CH2CH2CN from the anions -CH2CN, CH3-CHCN and -CH2CH2CN in the gas phase. A joint experimental and theoretical study

Franck-Condon one-electron oxidation of the stable anions -CH2CN, CH3-CHCN and -CH2CH2CN (in the collision cell of a reverse-sector mass spectrometer) produce the radicals .CH2CN, CH3.CHCN and .CH2CH2CN, which neither rearrange nor decompose during the microsecond duration of the neutralisation-reionisation experiment. Acetonitrile (CH3CN) and propionitrile (CH3CH2CN) are known interstellar molecules and radical abstraction of these could produce energised .CH2CN and CH3.CHCN, which might react with NH2. (a known interstellar radical) on interstellar dust or ice surfaces to form NH2CH2CN and NH2CH(CH3)CN, precursors of the amino acids glycine and alanine.     

A semi-empirical calculation of the potential surface for the CH 3 . +CH2=CH2 reaction

A model for the reaction CH ₃ ^. +CH₂=CH₂ is studied including the hybridization change of the reaction center. The interaction energy is devided into two parts. The first is a stabilization energy — the contribution due to the -electron delocalization (including the hybridization effects). It is computed by the PPP method. The second part is an exchange repulsion due to all valence electrons of the three carbon atoms. Correlation corrections are considered. A potential energy surface is constructed, giving a saddle point value close to the experimental activation energy. A discussion is given of the approximations involved. The method suggested is a generalization of the reactivity indices method of the theory of chemical reactivity. It can be regarded as a justification of this more empirical approach.

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Zusammenfassung Ein Modell für die Reaktion CH ₃ ^. +CH₂=CH₂ wird untersucht, einschließlich der Änderung der Hybridisation des Reaktionszentrums. Die Wechselwirkungsenergie wird in zwei Teile zerlegt. Der erste Teil ist eine Stabilisationsenergie — der Beitrag, der der Delokalisierung des -Elektrons (einschließlich Hybridisationseffekte) entspricht. Der zweite Teil ist eine Austauschabstoßung, die von allen Valenzelektronen der drei Kohlenstoffatome herrührt. Korrellationskorrekturen werden berücksichtigt. Eine Fläche der potentiellen Energie wird konstruiert mit einem Sattelpunktswert, der dicht an der experimentellen Aktivierungsenergie liegt. Die verwendeten Näherungsmethoden werden diskutiert. Die vorgeführte Methode ist eine Verallgemeinerung der Methode der Reaktivitätsindices aus der Theorie der chemischen Reaktivität. Sie kann als eine Rechtfertigung dieser mehr empirischen Näherung angesehen werden.

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Résumé Etude d'un modèle pour la réaction CH ₃ ^. +CH₂=CH₂ où l'on tient compte du changement d'hybridation du centre réactif. L'énergie d'interaction est divisée en deux termes. Le premier est une énergie de stabilisation; c'est la contribution dela délocalisation des électrons (effets d'hybridation compris). Il est calculé par la méthode PPP. Le second terme est une répulsion d'échange dûe à tous les électrons de valence des trois atomes de carbone. Les corrections de corrélation sont introduites.Une surface d'énergie potentielle est construite; elle fournit une valeur de l'énergie d'activation proche de celle obtenue expérimentalement. Les approximations utilisées sont discutées. La méthode proposée est une généralisation de celles des indices de réactivité. On peut la considérer comme justifiant cette approche plus empirique.

     

Isomerization of CH3O+=CHCH3 to CH2=O+CH2CH3

Ab initio calculations establish that CH₃O⁺=CHCH₃ (1) rearranges in gas phase isolation to CH₂=O⁺C₂H₅ (2) directly rather than through CH₃OCH₂CH ₂ ⁺ (3). The reaction is predicted to be antarafacial, in accord with the Woodward-Hoffmann (W-H) predictions. We predict an activation energy of 212.0 kJ/mol for this process at the QCISD(T)/6-311G**//MP2/6-311G** level. We also reinvestigated the degenerate rearrangement of CH₃O=CH ₂ ⁺ by a 1,3-sigmatropic shift. The W-H model is not a good one for the transition state (TS) for the latter reaction because the π bonding has been completely broken off. That TS is stabilized by three-center bonding between the carbons and the hydrogen being transferred. We also examined the questions of the importance of polarization functions on hydrogen and a set of outer valence functions on all the atoms in describing these hydrogen transfer TSs, and whether it is necessary to include these functions in the TS optimization runs. For the rearrangements we studied, polarization functions on hydrogen are crucial only for 1,2 hydrogen shifts. The 6-31G* basis set is adequate and good for the optimization of TSs of other ring sizes. For the 1,3 and 1,4 shifts we examined, a combination of both outer valence functions and polarization functions on hydrogen causes reductions in the computed activation energies ranging from 5.9 kJ/mol for the 1,4 shift at the RHF level to 15.6 kJ/mol for the 1,3 shift at the MP2 level.     

Synthesis and Characterization of （CH3CH2CH2CH2NH3）2SnBr6

1 INTRODUCTION Recently, the researches on inorganic-organic hy-brid compounds represent an advanced field in mate-rial science[1]. At the molecular level, the combina-tion of two extremely different components providesan avenue to design new hybrid materials as well asthe ability to modulate properties of one or more ofthe components[2～6]. Some attractive properties, suchas efficient luminescence[2～4], ideal thermal and me-chanical stability, interesting magnetic[5], non-linearoptical[…     

Kinetic and mechanistic study of the reactions of atomic chlorine with CH3CH2Br, CH3CH2CH2Br, and CH2BrCH2Br

A laser flash photolysis-resonance fluorescence technique has been employed to investigate the reactions of atomic chlorine with three alkyl bromides (R-Br) that have been identified as short-lived atmospheric constituents with significant ozone depletion potentials (ODPs). Kinetic data are obtained through time-resolved observation of the appearance of atomic bromine that is formed by rapid unimolecular decomposition of radicals generated via abstraction of a β-hydrogen atom. The following Arrhenius expressions are excellent representations of the temperature dependence of rate coefficients measured for the reactions Cl + CH(3)CH(2)Br (eq 1 ) and Cl + CH(3)CH(2)CH(2)Br (eq 2 ) over the temperature range 221-436 K (units are 10(-11) cm(3) molecule(-1) s(-1)): k(1)(T) = 3.73?exp(-378/T) and k(2)(T) = 5.14?exp(+21/T). The accuracy (2σ) of rate coefficients obtained from the above expressions is estimated to be ±15% for k(2)(T) and +15/-25% for k(1)(T) independent of T. For the relatively slow reaction Cl + CH(2)BrCH(2)Br (eq 3 ), a nonlinear ln k(3) vs 1/T dependence is observed and contributions to observed kinetics from impurity reactions cannot be ruled out; the following modified Arrhenius expression represents the temperature dependence (244-569 K) of upper-limit rate coefficients that are consistent with the data: k(3)(T) ≤ 3.2 × 10(-17)T(2)?exp(-184/T) cm(3) molecule(-1) s(-1). Comparison of Br fluorescence signal strengths obtained when Cl removal is dominated by reaction with R-Br with those obtained when Cl removal is dominated by reaction with Br(2) (unit yield calibration) allows branching ratios for β-hydrogen abstraction (k(ia)/k(i), i = 1,2) to be evaluated. The following Arrhenius-type expressions are excellent representations of the observed temperature dependences: k(1a)/k(1) = 0.85?exp(-230/T) and k(2a)/k(2) = 0.40 exp(+181/T). The accuracy (2σ) of branching ratios obtained from the above expressions is estimated to be ±35% for reaction 1 and ±25% for reaction 2 independent of T. It appears likely that reactions 1 and 2 play a significant role in limiting the tropospheric lifetime and, therefore, the ODP of CH(3)CH(2)Br and CH(3)CH(2)CH(2)Br, respectively.     

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     

Kinetics of the CH2Cl + CH3 and CHCl2 + CH3 radical-radical reactions

The CH2Cl + CH3 (1) and CHCl2 + CH3 (2) cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301-800 K and bath gas (helium) density (6-12) x 10(16) atom cm(-3). The observed rate constant of reaction 1 can be represented by an Arrhenius expression k1 = 3.93 x 10(-11) exp(91 K/T) cm3 molecule(-1) s(-1) (+/-25%) or as an average temperature-independent value of k1= (4.8 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The rate constant of reaction 2 can be expressed as k2= 1.66 x 10(-11) exp(359 K/T) cm3 molecule(-1) s(-1) (+/-25%). C2H4 and C2H3Cl were detected as the primary products of reactions 1 and 2, respectively. The experimental values of the rate constant are in reasonable agreement with the prediction based on the "geometric mean rule." A separate experimental attempt to determine the rate constants of the high-temperature CH2Cl + O2 (10) and CHCl2 + O2 (11) reaction resulted in an upper limit of 1.2 x 10(-16) cm(3) molecule(-1) s(-1) for k10 and k11 at 800 K.     

Secondary kinetics of methanol decomposition: theoretical rate coefficients for 3CH2 + OH, 3CH2 + 3CH2, and 3CH2 + CH3

Direct variable reaction coordinate transition state theory (VRC-TST) rate coefficients are reported for the (3)CH(2) + OH, (3)CH(2) + (3)CH(2), and (3)CH(2) + CH(3) barrierless association reactions. The predicted rate coefficient for the (3)CH(2) + OH reaction (approximately 1.2 x 10(-10) cm(3) molecule(-1) s(-1) for 300-2500 K) is 4-5 times larger than previous estimates, indicating that this reaction may be an important sink for OH in many combustion systems. The predicted rate coefficients for the (3)CH(2) + CH(3) and (3)CH(2) + (3)CH(2) reactions are found to be in good agreement with the range of available experimental measurements. Product branching in the self-reaction of methylene is discussed, and the C(2)H(2) + 2H and C(2)H(2) + H2 products are predicted in a ratio of 4:1. The effect of the present set of rate coefficients on modeling the secondary kinetics of methanol decomposition is briefly considered. Finally, the present set of rate coefficients, along with previous VRC-TST determinations of the rate coefficients for the self-reactions of CH(3) and OH and for the CH(3) + OH reaction, are used to test the geometric mean rule for the CH(3), (3)CH(2), and OH fragments. The geometric mean rule is found to predict the cross-combination rate coefficients for the (3)CH(2) + OH and (3)CH(2) + CH(3) reactions to better than 20%, with a larger (up to 50%) error for the CH(3) + OH reaction.     

Excess Molar Enthalpies of the Ternary System {x1CH3CH2COOCH2CH3+x2CH3(CH2)4CH3+(1-x1-x2)CH3CH2CH2OH} at 298.15 K,and Prediction Using Different Theoric Methods

Abstract

Excess molar enthalpies at the temperature 298.15 K and atmospheric pressure of the ternary mixture {x₁CH₃CH₂COOCH₂CH₃+x₂CH₃(CH₂)₄CH₃+(1-x₁-x₂)CH₃CH₂CH₂OH}and of the involved binary mixtures {xCH₃CH₂COOCH₂CH₃+(1-x)CH₃CH₂CH₂OH} and {xCH₃(CH₂)₄CH₃ + (1-x)CH₃CH₂CH₂OH}were measured using a Calvet microcalorimeter. Variable degree polynomials were fitted to the results. The group contribution models of Nitta-Chao and UNIFAC (versions of Tassios, Larsen and Gmehling) were used to estimate ternary excess enthalpy values, and the results were compared to the experimental data. Several empirical expressions for estimating ternary properties from binary results were also applied.     

Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals. II. Reactions of •CF3 +CF3CH2CH2• and CF3CH2CH2• + CF3CH2CH2•

Disproportionation/combination rate constant ratios, k_d /k_c, have been measured for the collision between CF₃CH₂CH₂ and CF₃ radicals to be 0.022 ± 0.002 and for CF₃CH₂CH₂ and CF₃CH₂CH₂ radicals to be 0.100 ± 0.002. Comparison to previous work from this laboratory for the reaction of CF₃CH₂CHCl with CF₃ radicals shows that substitution of Cl for H increases the k_d /k_c by about 50%; however, for the auto disproportionation-combination of CF₃CH₂CH₂ radicals the chlorine substituent decreases the observed rate constant ratio by a factor of two. The chlorine substituent effect on the observed k_d /k_c ratios is compared to predictions from molecular orbital calculations. © 1996 John Wiley & Sons, Inc.     

Determination of the isomerization rate constant HOCH2CH2CH2CH(OO·)CH3 →HOC·HCH2CH2CH(OOH)CH3. Importance of intramolecular hydroperoxy isomerization in tropospheric chemistry

The rate constant of the title reaction is determined during thermal decomposition of di-n-pentyl peroxide C₅H₁₁O( )OC₅H₁₁ in oxygen over the temperature range 463–523 K. The pyrolysis of di-n-pentyl peroxide in O₂/N₂ mixtures is studied at atmospheric pressure in passivated quartz vessels. The reaction products are sampled through a micro-probe, collected on a liquid-nitrogen trap and solubilized in liquid acetonitrile. Analysis of the main compound, peroxide C₅H₁₀O₃, was carried out by GC/MS, GC/MS/MS [electron impact EI and NH₃ chemical ionization CI conditions]. After micro-preparative GC separation of this peroxide, the structure of two cyclic isomers (3S*,6S*)3α-hydroxy-6-methyl-1,2-dioxane and (3R*,6S*)3α-hydroxy-6-methyl-1,2-dioxane was determined from ¹H NMR spectra. The hydroperoxy-pentanal OHC( )(CH₂)₂( )CH(OOH)( )CH₃ is formed in the gas phase and is in equilibrium with these two cyclic epimers, which are predominant in the liquid phase at room temperature. This peroxide is produced by successive reactions of the n-pentoxy radical: a first one generates the CH₃C·H(CH₂)₃OH radical which reacts with O₂ to form CH₃CH(OO·)(CH₂)₃OH; this hydroxyperoxy radical isomerizes and forms the hydroperoxy HOC·H(CH₂)₂CH(OOH)CH₃ radical. This last species leads to the pentanal-hydroperoxide (also called oxo-hydroperoxide, or carbonyl-hydroperoxide, or hydroperoxypentanal), by the reaction HOC·H(CH₂)₂CH(OOH)CH₃+O₂→O()CH(CH₂)₂CH(OOH)CH₃+HO₂. The isomerization rate constant HOCH₂CH₂CH₂CH(OO·)CH₃→HOC·HCH₂CH₂CH(OOH)CH₃ (k₃) has been determined by comparison to the competing well-known reaction RO₂+NO→RO+NO₂ (k₇). By adding small amounts of NO (0–1.6×10¹⁵ molecules cm⁻³) to the di-n-pentyl peroxide/O₂/N₂ mixtures, the pentanal-hydroperoxide concentration was decreased, due to the consumption of RO₂ radicals by reaction (7). The pentanal-hydroperoxide concentration was measured vs. NO concentration at ten temperatures (463–523 K). The isomerization rate constant involving the H atoms of the CH₂( )OH group was deduced: or per H atom: The comparison of this rate constant to thermokinetics estimations leads to the conclusion that the strain energy barrier of a seven-member ring transition state is low and near that of a six-member ring. Intramolecular hydroperoxy isomerization reactions produce carbonyl-hydroperoxides which (through atmospheric decomposition) increase concentration of radicals and consequently increase atmospheric pollution, especially tropospheric ozone, during summer anticyclonic periods. Therefore, hydrocarbons used in summer should contain only short chains (<C₄) hydrocarbons or totally branched hydrocarbons, for which isomerization reactions are unlikely. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 875–887, 1998     

Kinetic study of the reactions of Cl atoms with CF3CH2CH2OH, CF3CF2CH2OH, CHF2CF2CH2OH, and CF3CHFCF2CH2OH

The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF(3)CH(2)CH(2)OH (1), CF(3)CF(2)CH(2)OH (2), CHF(2)CF(2)CH(2)OH (3), and CF(3)CHFCF(2)CH(2)OH (4), were studied in the gas phase over the temperature range of 273-363 K by using very low-pressure reactor mass spectrometry. The absolute rate coefficients were given by the expressions (in cm(3) molecule(-1) s(-1)): k(1) = (4.42 +/- 0.48) x 10(-11) exp(-255 +/- 20/T); k(1)(303) = (1.90 +/- 0.17) x 10(-11), k(2) = (2.23 +/- 0.31) x 10(-11) exp(-1065 +/- 106/ T); k(2)(303) = (6.78 +/- 0.63) x 10(-13), k(3) = (8.51 +/- 0.62) x 10(-12) exp(-681 +/- 72/T); k(3)(303) = (9.00 +/- 0.82) x 10(-13) and k(4) = (6.18 +/- 0.84) x 10(-12) exp(-736 +/- 42/T); k(4)(303) = (5.36 +/- 0.51) x 10(-13). The quoted 2sigma uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis mechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and the end products were the corresponding aldehydes (R(F)-CHO; R(F) = -CH(2)CF(3), -CF(2)CF(3), -CF(2)CHF(2), and -CF(2)CHFCF(3)), providing a strong experimental indication that the primary reactions proceed mainly via the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and ionization potentials for the title compounds were determined by density functional theory calculations, which also suggest that the alpha-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of room-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated C2-C5 ethers and C2-C4 alcohols, is good with an average deviation of a factor of 2, and is given by the expression log(k) (in cm(3) molecule(-1) s(-1)) = (5.8 +/- 1.4) - (1.56 +/- 0.13) x (ionization potential (in eV)).     

Ab initio study of the spectroscopy of CH3N and CH3CH2N

Complete active space (CAS) calculations with 6-311++g(3df,3pd) basis sets were performed for a large number of electronic states of the nitrate free radical (CH3N/CH3CH2N) and their positive and negative ions. All calculated states are valence states, and their characters are discussed in detail. To investigate the Jahn-Teller effect on the CH3N radical, Cs symmetry was used for both CH3N and CH3CH2N in calculations. The results (CASPT2 adiabatic excitation energies and CASSI oscillator strengths) suggest that the calculated transitions of CH3N at 32172 and 32139 cm(-1) are attributed to the 2(3)A' ' --> 1(3)A' ' and 1(3)A' --> 1(3)A' ', respectively, which is in accordance with the A3E --> X3A2 emission spectrum at T0 = 31 817 cm(-1). The calculated transitions of CH3CH2N at 334 nm are attributed to the 1(3)A' ' --> 2(3)A' ' and 1(3)A' ' --> 1(3)A', respectively, which is in accordance with the UV absorption spectrum of a series of 11 bands beginning at 335 nm. The vertical and adiabatic ionization energies were obtained to compare with the PES data. These results are in agreement with previous experimental data, which is discussed in detail.     

CH3NO2和CH3自由基吸氢反应途径和变分速率常数计算

采用MP2(full)/6-311G(d,p)从头算方法,优化了硝基甲烷和甲基自由基吸氢反应的过渡态结构,经QCISD(T)方法进行能量校正,得出该反应的正逆向反应的活化位垒分别是58.21kJ@mol-1和67.17kJ@mol-1.沿IRC分析指出该反应是氢转移协同反应,而且在反应途径上存在一个引导反应进行的振动模式,这一反应模式引导反应进行的区间在反应坐标S的-0.9～1.0(amu)1/2bohr之间;在温度为800～2600K范围内,运用改进的变分过渡态理论(ICVT),计算了该反应的速率常数,并与实验类比所得的速率常数随温度的变化趋势进行了比较.     

Lithiation of the Tin-containing Sulfone Me3SnCH2CH2CH2SO2C6H4CH3-4

The tin-containing sulfide Me₃Sn(CH₂)₃-S-C₆H₅CH₃-4 obtained by photoaddition of 4-toluene- thiol to allyltrimethyltin was oxidized with hydrogen peroxide to synthesize the tin-containing sulfone Me₃Sn(CH₂)₃-SO₂-C₆H₄CH₃-4, the tin and sulfur atoms in which are separated by a trimethylene bribge. Treatment of the sulfone with butyllithium gave a first tin-containing lithium salt having a red-brown color. The exchange reaction of this salt with methyl iodide resulted in formation of two new isomeric tin-containing sulfones Me₃SnCH₂CH₂CH(CH₃)-SO₂-C₆H₄CH₃ and Me₃Sn(CH₂)₃-SO₂-C₆H₄CH₂CH₃ identified by ^1HNMR spectroscopy. The latter result implies that the tin-containing sulfone is lithiated both by the methylene group adjacent to the sulfonyl group and by the toluene methyl group.     

Direct dynamics studies on hydrogen abstraction reactions of CH3CHFCH3 and CH3CH2CH2F with OH radicals

The hydrogen abstraction reactions of CH3CHFCH3 and CH3CH2CH2F with the OH radicals have been studied theoretically by a dual-level direct dynamics method. The geometries and frequencies of all the stationary points are optimized by means of the DFT calculation. There are complexes at the reactant side or exit route, indicating these reactions may proceed via indirect mechanisms. To improve the reaction enthalpy and potential barrier of each reaction channel, the single point energy calculation is performed by the MC-QCISD/3 method. The rate constants are evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT) over a wide temperature range 200-2000 K. The canculated CVT/SCT rate constants are consistent with available experimental data. The results show that both the variation effect and the SCT contribution play an important role in the calculation of the rate constants. For reactions CH3CHFCH3 and CH3CH2CH2F with OH radicals, the channels of H-abstraction from -CHF- and -CH2- groups are the major reaction channels, respectively, at lower temperature. Furthermore, to further reveal the thermodynamics properties, the enthalpies of formation of reactants CH3CHFCH3, CH3CH2CH2F, and the product radicals CH3CFCH3, CH3CHFCH2, CH3CH2CHF, CH3CHCH2F, and CH2CH2CH2F are studied using isodesmic reactions.     

NMR investigations on Stannabicycloundecanes of the type RSn(CH2CH2CH2)3N

The ¹H, ¹³C, and ¹¹⁹Sn NMR data of seven stannabicycloundecanes of the type RSn(CH₂CH₂CH₂)₃N (1, R = Cl; 2 , R = Br; 3 , R = I; 4 , R = OH; 5 , R = SPh; 6 , R = Me; 7 , R = Sn(CH₂CH₂CH₂)₃N) are reported. From ¹H NMR coalescence data at low temperature the free activation enthalpies for the racemisation of the bicyclo[3.3.3]skeleton were estimated to be 37 ± 1 kJ/mol. They are independent of the substituent R. However, it decreases when the tin atom is replaced by silicon for R = Me.