Ru and Sm catalyzed polyaddition of dialdehydes to give polyesters. Application of Tishchenko type reactions to polymer synthesis

RuH₂(PPh₃)₄ catalyzed Tishchenko type polyaddition of terephthal-aldehyde gives aromatic polyester ( 1 ), which contains three structural units, [OCH₂ C₆H₄ CH₂O] ( 1a ), [OCH₂ C₆H₄ CO] ( 1b ), and [CO C₆H₄ CO] ( 1c ). ¹H-NMR spectrum shows the presence of the three units in a 1 : 2 : 1 ratio. Isophthalaldehyde also undergoes similar polyaddition to give another aromatic polyester ( 2 ), while 1,12-dodecanedial gives an aliphatic polyester ( 3 ) containing the following structural units: [OCH₂ (CH₂)₁₀ CH₂O] ( 3a ), [OCH₂ (CH₂)₁₀ CO] ( 3b ), and [CO (CH₂)₁₀ CO] ( 3c ). The above polymers have M_n of 2.7 × 10³−5.4 × 10³ and M_w of 4.3 × 10³ − 9.7 × 10³, respectively. Mixtures of terephthalaldehyde and 1,12-dodecanedial produce copolymers, which contain the units 1a–1c and 3a–3c in a random sequence. In the copolymerization, terephthalaldehyde shows a strong tendency to give 1c units, whereas 1,12-dodecanedial predominantly affords 3a units. SmI₂ also catalyzes polyaddition of terephthalaldehyde to give the corresponding polyester with M_n of 1.7 × 10³ and M_w of 3.7 × 10³, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1265–1273, 1997     

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.     

The tautomerization and ring closure in the Claisen rearrangement: A DFT study

Elementary processes of the aromatic Claisen rearrangement were investigated by DFT calculations. First, rearrangements of four substrates Ph—O—CH₂—CHCH₂ [A], Ph—O—CH₂—CHCH(OMe) [B], Ph—O—CH₂—CHCH₂····BF₃ [C], and Ph—O—CH—CHCH(OMe)····BF₃ [D] were examined. In these systems, the tautomerization is initiated by the intermolecular proton transfer involving the transient ion‐pair intermediate. An ignition‐propagation chain‐reaction mechanism in the tautomerization was suggested. For [A], the (ortho‐allyl phenol → α‐methyl‐dihydrobenzofuran (α‐methyl‐cumarane)) process was found to be ready and the product of the Claisen rearrangement seems to be the cumarane rather than the phenol. In [D] (activated both by the terminal methoxy group and by the BF₃ catalyst), not the [3,3]‐sigmatropic shift but the tautomerization is the rate determining step. Second, the parent system, Ph—O—CH₂—CHCH₂, was investigated with (H₂O) _n (n = 2, 4, 6, and 10) systematically. The tautomerization takes place by the proton transfer via the water dimer or trimer. Except n = 2, similar changes of Gibbs free energies were obtained from the ether substrate to the cumarane.     

Synthesis of high‐molecular‐weight elastomeric poly(propylene) with half‐titanocene/MAO catalyst

A novel catalyst precursor, (η⁵‐pentamethylcyclopentadienyl)titanium triallyloxide (Cp*Ti(OCH₂—CH=CH₂)₃), was prepared and employed in a study of propylene polymerization in the presence of methylaluminoxane (MAO). This work has revealed that the half‐titanocene catalyst is desirable for the production of elastomeric poly(propylene) with high molecular weight (M_w = 8–69×10⁴) as well as in good yields under typical polymerization conditions.     

Preparation of poly(aryleneethynylene)–type copolymers containing flexible linking methylene units. Optical properties of the copolymers suggesting occurrence of energy transfer between π–conjugated local units

Palladium–catalyzed polycondensation between 2,5–diiodo–3–hexylthiophene I–Th(Hex)–I with mixtures of p–diethynylbenzene HCC—Ph—CCH and α,ω–diethynylalkane HCC(CH₂)_lCCH (l = 3 or 8) gives poly(aryleneethynylene) PAE–type copolymers [CC(CH₂)_lCC—Th(Hex)]_m[CC—Ph—CC—Th(Hex)]_n containing the methylene unit. The copolymers have a molecular weight (M_n) of about 1.2 × 10⁴ as determined by GPC (polystyrene standard) and are considered to possess essentially a random sequences in view of the —CC(CH₂)_lCC— and —CC—Ph—CC— units as judged from their UV–visible spectra. By the incorporation of the (CH₂)_l unit, the λ_max position of the corresponding PAE homopolymer [CC—Ph—CC—Th(Hex)]_n is shifted to a shorter wavelength. However, the copolymers give rise to a photoluminescence PL peak essentially agreeing with a PL peak of the homopolymer, suggesting occurrence of energy transfer in the copolymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2201–2207, 1998     

Solubility of polystyrene in selectively deuterated methyl acetate

Cloud point measurements were made for binary systems of polystyrene (PS) + methyl acetate (MA) and polystyrene (PS) + selectively deuterated MA: CD₃COOCH₃ and CH₃COOCD₃ with three PS samples of M_w = 4.0 × 10⁵, 2.0 × 10⁶, and 13.2 × 10⁶. All systems are characterized by the phase diagrams with upper and lower critical temperature. H/D isotope effects on miscibility for both selectively deuterated acetates are very large and appeared to be independent of the site of deuterium substitution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2140–2143, 2009     

Theoretical Studies of the Reactions CFxH3−xCOOR+Cl and CF3COOCH3+OH

The mechanism and kinetics of the reactions of CF₃COOCH₂CH₃, CF₂HCOOCH₃, and CF₃COOCH₃ with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06‐2X methods with the 6‐311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6‐311++G(d,p) methods. Seven hydrogen‐abstraction channels are found. All the rate constants, computed by a dual‐level direct method with a small‐curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low‐temperature range. For the reaction of CF₃COOCH₂CH₃+Cl, H‐abstraction from the CH₂ group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200–1000 K as k_T(1)=8.4×10^?20T ^2.63exp(381.28/T), k_T(2)=2.95×10^?21T ^3.13exp(?103.21/T), k_T(3)=1.25×10^?23T ^3.37exp(791.98/T), and k_T(4)=4.53×10^?22T ^3.07exp(465.00/T).     

Reactivity of selected volatile organic compounds (VOCs) toward the sulfate radical (SO4−)

Rate constants for a series of alcohols, ethers, and esters toward the sulfate radical (SO₄^?) have been directly determined using a laser photolysis set‐up in which the radical was produced by the photodissociation of peroxodisulfate anions. The sulfate radical concentration was monitored by following its optical absorption by means of time resolved spectroscopy techniques. At room temperature the following rate constants were derived: methanol ((1.6 ± 0.2) × 10⁷ M^?1 s^?1); ethanol ((7.8 ± 1.2) × 10⁷ M^?1 s^?1); tert‐butanol ((8.9 ± 0.3) × 10⁵ M^?1 s^?1); diethyl ether ((1.8 ± 0.1) × 10⁸ M^?1 s^?1); MTBE ((3.13 ± 0.02) × 10⁷ M^?1 s^?1); tetrahydrofuran (THF) ((2.3 ± 0.2) × 10⁸ M^?1 s^?1); hydrated formaldehyde ((1.4 ± 0.2) × 10⁷ M^?1 s^?1); hydrated glyoxal ((2.4 ± 0.2) × 10⁷ M^?1 s^?1); dimethyl malonate (CH₃OC(O)CH₂C(O)OCH₃) ((1.28 ± 0.02) × 10⁶ M^?1 s^?1); and dimethyl succinate (CH₃OC(O)CH₂CH₂C(O)OCH₃) ((1.37 ± 0.08) × 10⁶ M^?1 s^?1) where the errors represent 2σ. For the two latter species, we also measured the temperature dependence of the corresponding rate constants. A correlation of these kinetics with the bond dissociation energy is also presented and discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 539–547, 2001     

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     

Rate constants for the reactions of chlorine atoms with hydrochloroethers at 298 k and atmospheric pressure

The relative rate technique has been used to determine the rate constants for the reactions Cl + CH₃OCHCl₂ → products and Cl + CH₃OCH₂CH₂Cl → products. Experiments were carried out at 298 ± 2 K and atmospheric pressure using nitrogen as the bath gas. The decay rates of the organic species were measured relative to those of 1,2‐dichloroethane, acetone, and ethane. Using rate constants of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1, (2.4 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1, and (5.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 for the reactions of Cl atoms with 1,2‐dichloroethane, acetone, and ethane respectively, the following rate coefficients were derived for the reaction of Cl atoms (in units of cm³ molecule^?1 s^?1) with CH₃OCHCl₂, k= (1.04 ± 0.30) × 10^?12 and CH₃OCH₂CH₂Cl, k= (1.11 ± 0.20) × 10^?10. Errors quoted represent two σ, and include the errors due to the uncertainties in the rate constants used to place our relative measurements on an absolute basis. The rate constants obtained are compared with previous literature data and used to estimate the atmospheric lifetimes for the studied ethers. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 420–426, 2005     

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.     

Easily available niobium(V) mixed chloro‐alkoxide complexes as catalytic precursors for ethylene polymerization

The dinuclear [NbCl_n(OR)_(5‐n)]₂ (n = 4, R = Et, 1 ; n = 4, R = CH₂Ph, 2 ; n = 3, R = Et, 3 ; n = 2, R = Et, 4 ; n = 2, R = , 5 ), and [Nb(OEt)₅]₂, 6 , and the mononuclear niobium compounds NbCl₄[κ²? OCH₂CH(R′)OR] (R = Me, R′ = H, 7 ; R = Et, R′ = H, 8 ; R = CH₂Cl, R′ = H, 9 ; R = CH₂CH₂OMe, R′ = H, 10 ; R = R′ = Me, 11 ), NbBr₄[κ²? OCH₂CH₂OMe], 12 , and NbCl₃(κ²? OCH₂CH₂OMe)(κ¹? OCH₂CH₂OMe), 13 , were tested in ethylene polymerization. Optimized reaction conditions included the use of D‐MAO as co‐catalyst and chlorobenzene as solvent at 50 °C. Complex 7 , whose X‐Ray structure is described here for the first time, exhibited the highest activity ever reported for a niobium catalyst in alkene polymerization [151 kg_polymer × mol_Nb^?1 × h^?1 × bar^?1]. Compounds 1 , 3‐5 , 8 , 13 showed activities similar to that of 7 . Linear polyethylenes (characterized by FT‐IR, NMR, GPC, and DSC analyses) with a broad polydispersivity were obtained. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Unimolecular reactions of ionized methyl acetate and its hydrogen-rearranged isomers

The proposed formation of [CH₃C(OH)OCH₂]⁺˙ (b) as the intermediate in the isomerization [CH₂?C(OH)OCH₃]⁺˙ (c)?b?[CH₃COOCH₃]⁺˙ (c has been confirmed by preparation of b from CH₃COOCH₂OCH₃. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH₃O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a?b and b?c must be nearly as high as that for CH₃O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH₂?C(OD)OCH₃]⁺˙ and c–D₃ ions confirm this, indicating that the barrier for a?b is slightly below that for b?c. Minor low-energy dissociations include losses of CH₄ and CH₃OH from a and losses of ˙CHO and CH₂O from b. Comparison of MI and CAD spectra of a–c with those from [CH₃(OH)CH₂O]⁺˙ (d) and [CH₃COCH₂OH]⁺˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.     

Self‐polyaddition of triethylsilyl perfluoroisopropenyl ether

The results on radical self‐polyaddition reactivity of two trialkylsilyl perfluoroisopropenyl ethers, triethysilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(C₂H₅)₃] (FTEE) and dimethylphenylsilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(CH₃)₂C₆H₅] (DMPE), and two perfluoroisopropenyl carboxylates, 2‐butyroxypentafluoropropene [CF₂?C(CF₃)OCOC₃H₇] (BuFPP) and 2‐(methoxyacetoxy)pentafluoropropene [CF₂?C(CF₃)OCOCH₂OCH₃] (MFPP), are described. Radical self‐polyaddition of FTEE afforded a polymer as high as 1.87 × 10⁴ in molecular weight in the presence of radical generators such as benzoyl peroxide and di‐tert‐butyl peroxide. DMPE gave only addition products with initiating radicals. BuFPP and MFPP scarcely yielded even addition products with radical. The mechanism that the self‐polyaddition of FTEE was initiated by the addition of radical onto the perfluoroisopropenyl group followed by a 1,5‐shift to afford a methyl radical that attacked the perfluoroisopropenyl group of another FTEE molecule is proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2743–2754, 2003     

Synthesis and1H NMR study of some organotin derivatives of diethanolamines

A number of organotin derivatives of diethanolamines (stannocanes) R₂Sn(OCH₂CH₂)₂NR', O(SiMe₂CH₂)₂Sn(OCH₂CH₂)₂NR', and Sn[(OCH₂CH₂)₂NR']₂ (R = Ph,cyclo-Hex; R' = H, Me, Ph) were synthesized and studied by¹H NMR spectroscopy. The effect of steric factors on the ability of molecules of stannocanes to form associates in solutions is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.714–718, April, 1994.     

REACTIONS OF A PHOSPHORANIMINE ANION WITH SOME ORGANIC ELECTROPHILES

Abstract

The reactions of a variety of electrophiles with the N-silyl-P-trifluoroethoxyphosphoranimine anion Me₃Sin°P(Me)(OCH₂CF₃)CH^? ₂ (1a), prepared by the deprotonation of the dimethyl precursor Me₃SiN[dbnd]P(OCH₂CF₃)Me₂ (1) with n-BuLi in Et₂O at-78°C, were studied. Thus, treatment of 1a with alkyl halides, ethyl chloroformate, or bromine afforded the new N-silylphosphoranimine derivatives Me₃SiN[dbnd]P(Me)(OCH₂CF₃)CH₂R [2: R = Me, 3: R = CH₂Ph, 4: R = CH[sbnd]CH₂, 5: R = C(O)OEt, and 6: R = Br]. In another series, when 1a was allowed to react with various carbonyl compounds, 1,2-addition of the anion to the carbonyl group was observed. Quenching with Me₃SiCl gave the O-silylated products Me₃SiN[dbnd]P(Me)(OCH₂CF₃)CH₂°C(OSiMe₃)R¹R² [7: R ¹ = R ² = Me; 8: R ¹ = Me, R ² = Ph; 9: R¹ = Me, R ² = CH[sbnd]CH₂; and 10: R ¹ = H, R ² = Ph]. Compounds 2–10 were obtained as distillable, thermally stable liquids and were characterized by NMR spectroscopy (¹H, ¹³C, and ³¹P) and elemental analysis.     

Couloamperometry. A fast kinetic technique for halogenations. I. Bromination rate constants of highly reactive enol ethers

A new couloamperometric apparatus has been designed to extend the range of this kinetic technique to the measurement of very high rate constants, 10⁸M^?1s^?1, by using TFCR-EXSEL conditions (TFCR—very low reactant concentration; EXSEL—salt excess), which give half-lives of a few seconds for very fast second-order reactions. Very low faradaic currents, in the nanoampere range for halogens, corresponding to very low reactant concentrations of 10^?8–10^?9M, are measured selectively by compensating the eddy currents, principally the residual and the induced currents. When the electroactive species is bromine, the concentration is demonstrated to be linearly related to the limiting reduction current in the very low concentration range. The upper limit of this technique for bromination is at present 3 × 10⁸M^?1s^?1. The method is applied to the kinetic study of highly reactive enol ethers EtO-C(R) = CH-R′, where R and R′ are H or Me. A value of 2.2 × 10⁸M^?1s^?1 is obtained for k, the rate constant for free bromine addition to EtO-CH = CH₂, by extrapolating the kinetic bromide ion effects to [Br^?] = 0. An α-methyl effect (k_α-Me/k_H)_EtO of 15 is found; this is a small decrease in the methyl effect compared to the marked increase in the double bond reactivity. For the enol acetate MeCOO-CH = CH₂, whose rate constant is 6 × 10²M^?1s^?1, (k_α-Me/k_H)_OCOMe is 21. The dependence of substituent effects on reactivity is discussed in terms of the Hammond effect on the transition state position and of charge delocalization by group G of olefins G-CH = CH₂.     

The kinetics of the reactions of O(3P) atoms with dimethyl ether and methanol

The kinetics of the reaction of O + CH₃OCH₃ were investigated using fast-flow apparatus equipped with ESR and mass-spectrometric detection. The concentration of O(³P) atoms to CH₃OCH₃ was varied over an unusually large range. The rate constant for reaction was found to be k = (5.0 ± 1.0) × 10¹² exp [(?2850 ± 200/RT)] cm³ mole^?1 sec^?1. The reaction O + CH₃OH was studied using ESR detection. Based on an assumed stoichiometry of two oxygen atoms consumed per molecule of CH₃OH which reacts, we obtain a value of k = (1.70 ± 0.66) × 10¹² exp [(?2,280 ± 200/RT)] cm³ mole^?1 sec^?1 for the reaction The results obtained in this study are compared with the results from other workers on these reactions. The observation of essentially equal activation energies in these two reactions is indicative of approximately equal C? H bond strengths in CH₃OCH₃ and CH₃OH. This is in agreement with recent measurements of these bond energies.     

FT‐IR kinetic and product study of the OH radical and Cl‐atom–initiated oxidation of dibasic esters

Using a relative kinetic technique, rate coefficients have been measured, at 296 ± 2 K and 740 Torr total pressure of synthetic air, for the gas‐phase reaction of OH radicals with the dibasic esters dimethyl succinate [CH₃OC(O)CH₂CH₂C(O)OCH₃], dimethyl glutarate [CH₃OC(O)CH₂CH₂CH₂C(O)OCH₃], and dimethyl adipate [CH₃OC(O)CH₂CH₂CH₂CH₂C(O)OCH₃]. The rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (1.89 ± 0.26) × 10^?12; dimethyl glutarate (2.13 ± 0.28) × 10^?12; and dimethyl adipate (3.64 ± 0.66) × 10^?12. Rate coefficients have been also measured for the reaction of chlorine atoms with the three dibasic esters; the rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (6.79 ± 0.93) × 10^?12; dimethyl glutarate (1.90 ± 0.33) × 10^?11; and dimethyl adipate (6.08 ± 0.86) × 10^?11. Dibasic esters are industrial solvents, and their increased use will lead to their possible release into the atmosphere, where they may contribute to the formation of photochemical air pollution in urban and regional areas. Consequently, the products formed from the oxidation of dimethyl succinate have been investigated in a 405‐L Pyrex glass reactor using Cl‐atom–initiated oxidation as a surrogate for the OH radical. The products observed using in situ Fourier transform infrared (FT‐IR) absorption spectroscopy and their fractional molar yields were: succinic formic anhydride (0.341 ± 0.068), monomethyl succinate (0.447 ± 0.111), carbon monoxide (0.307 ± 0.061), dimethyl oxaloacetate (0.176 ± 0.044), and methoxy formylperoxynitrate (0.032–0.084). These products account for 82.4 ± 16.4% C of the total reaction products. Although there are large uncertainties in the quantification of monomethyl succinate and dimethyl oxaloacetate, the product study allows the elucidation of an oxidation mechanism for dimethyl succinate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 431–439, 2001     

Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with Cl

A dual‐level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF₂CF₂OCH₃ (HFE‐254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6‐311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H‐abstraction channels have been identified. For the reactant CHF₂CF₂OCH₃ and the two products, CHF₂CF₂OCH₂ and CF₂CF₂OCH₃, the standard enthalpies of formation are evaluated with the values of ?256.71 ± 0.88, ?207.79 ± 0.12, and ?233.43 ± 0.88 kcal/mol, respectively, via group‐balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition‐state theory (CVT) including the small‐curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k₁ = 9.22 × 10^?19 T^2.06 exp(219/T), k₂ = 4.45 × 10^?14 T^0.90 exp(?2220/T), and k = 4.71 × 10^?22 T^3.20) exp(543/T) cm³ molecule^?1 s^?1. Our results indicate that H‐abstraction from ? CH₃ group is the main reaction pathway in the lower temperature range, while H‐abstraction from ? CHF₂ group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221–230, 2007