Molecular properties of poly(2-deoxy-2-methacryloylamino-D-glucose) in aqueous solvents of various compositions

Six samples of poly(2-deoxy-2-methacryloylamino-D-glucose) were prepared by free-radical polymerization of the monomer. The molecular properties of the homologous series obtained were studied in three solvents, 0.2 M NaCl, 0.1 M Na₂SO₄, and salt-free water, by viscometry and static and dynamic light scattering. The Mark-Kuhn-Houwink relationships were obtained. The poly(vinyl saccharide) studied, despite the presence of bulky pendant substituents, is a typical flexible-chain polymer with the Kuhn segment length of 20 ± 3 Å. In aqueous salt systems, poly(2-deoxy-2-methacryloylamino-D-glucose), which is not a polyelectrolyte, nevertheless demonstrates the dependence of the hydrodynamic size of the molecules on the solvent composition. The SO ₄ ^2? ions make the polymer molecules more compact, whereas Cl^? ions present in aqueous solution lead to its expanding. Salt additions affect the thermodynamic quality of the polymer-solvent system.     

Very low-pressure pyrolysis (VLPP) of pentynes. II. 4-methylpent-2-yne and 4,4-dimethylpent-2-yne. Heats of formation and resonance stabilization energies of methyl-substituted propargyl radicals

Studies of the unimolecular decomposition of 4-methylpent-2-yne (M2P) and 4,4-dimethylpent-2-yne (DM2P) have been carried out over the temperature range of 903–1246 K using the technique of very-low pressure pyrolysis (VLPP). The primary reaction for both compounds is fission of the C? C bond adjacent to the acetylenic group producing the resonance-stabilized methyl-substituted propargyl radicals, CH₃C??H(CH₃) from M2P and CH₃C?C?(CH₃)₂ from DM2P. RRKM calculations were performed in conjunction with both vibrational and hindered rotational models for the transition state. Employing the usual assumption of unit efficiency for gas-wall collisions, the results show that only the rotational model with a temperature-dependent hindrance parameter gives a proper fit to the VLPP data over the entire experimental temperature range. The high-pressure Arrhenius parameters at 1100 K are given by the rate expressions log k₂ (sec^?1) = (16.2 ± 0.3) ? (74.4 ± 1.5)/θ for M2P and log k₃ (sec^?1) = (16.4 ± 0.3) ? (71.4 ± 1.5)/θ for DM2P where θ = 2.303RT kcal/mol. The A factors were assigned from the results of recent shock-tube studies of related alkynes. Inclusion of a decrease in gas-wall collision efficiency with temperature would lower both activation energies by ～1 kcal/mol. The critical energies together with the assumption of zero activation energy for recombination of the product radicals at 0 K lead to DH⁰[CH₃CCCH(CH₃)? CH₃] = 76.7 ± 1.5, ΔH_f⁰[CH₃CCCH(CH₃)] = 65.2 ± 2.3, DH⁰[CH₃CCCH(CH₃)? H] = 87.3 ± 2.7, DH⁰[CH₃CCC(CH₃)₂? CH₃] = 72.5 ± 1.5, ΔH[CH₃CC?(CH₃)₂] = 53.0 ± 2.3, and DH⁰[CH₃CCC(CH₃)₂? H] = 82.3 ± 2.7, where all quantities are in kcal/mol at 300 K. The resonance stabilization energies of the 1,3-dimethylpropargyl and 1,1,3-trimethylpropargyl radicals are 7.7 ± 2.9 and 9.7 ± 2.9 kcal/mol at 300 K. Comparison with results obtained previously for other propargylic radicals indicates that methyl substituents on both the radical center and the terminal carbon atom have little effect on the propargyl resonance energy.     

Kinetic study of the reaction of OH with a series of acetals at 298 ± 4 K

Rate coefficients have been measured at 298 ± 4 K and 1000 mbar total pressure for the reactions of OH with a series of symmetrical acetals (R O CH₂ O R, R = C₁ to C₄) using a relative kinetic technique. The investigations have been performed in a laboratory photoreactor and also in the large outdoor EUPHORE simulation chamber facility in Valencia, Spain. The following rate coefficients (in units of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹) have been obtained: dimethoxy methane (R = CH₃), 0.49 ± 0.02; diethoxy methane (R = CH₃CH₂), 1.84 ± 0.18; di‐n‐propoxy methane (R = CH₃CH₂CH₂), 2.63 ± 0.49; di‐iso‐propoxy methane (R = (CH₃)₂CH), 3.93 ± 0.48; di‐n‐butoxy methane (R = CH₃CH₂CH₂CH₂), 3.47 ± 0.42; di‐iso‐butoxy methane (R = (CH₃)₂CHCH₂), 3.68 ± 0.57; di‐sec‐butoxy methane (R = CH₃CH₂C(CH₃)H), 4.68 ± 0.05. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 797–803, 1999     

Rate coefficients and mechanisms of the reaction of cl‐atoms with a series of unsaturated hydrocarbons under atmospheric conditions

Rate coefficients and/or mechanistic information are provided for the reaction of Cl‐atoms with a number of unsaturated species, including isoprene, methacrolein ( MACR ), methyl vinyl ketone ( MVK ), 1,3‐butadiene, trans‐2‐butene, and 1‐butene. The following Cl‐atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 ± 0.6) × 10^?10cm³ molecule^?1 s^?1 (independent of pressure from 6.2 to 760 Torr); k( MVK ) = (2.2 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k( MACR ) = (2.4 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k(trans‐2‐butene) = (4.0 ± 0.5) × 10^?10 cm³ molecule^?1 s^?1; k(1‐butene) = (3.0 ± 0.4) × 10^?10 cm³ molecule^?1 s^?1. Products observed in the Cl‐atom‐initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH₂O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1‐chloro‐3‐methyl‐3‐buten‐2‐one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO₂ (58 ± 5%), CH₂O (47 ± 7%), CH₃OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK ; CO (52 ± 4%), chloroacetone (42 ± 5%), CO₂ (23 ± 2%), CH₂O (18 ± 2%), and HCOCl (5%) from MACR ; CH₂O (7 ± 1%), HCOCl (3%), acrolein (≈3%), and 4‐chlorocrotonaldehyde (CCA, not quantified) from 1,3‐butadiene; CH₃CHO (22 ± 3%), CO₂ (13 ± 2%), 3‐chloro‐2‐butanone (13 ± 4%), CH₂O (7.6 ± 1.1%), and CH₃OH (1.8 ± 0.6%) from trans‐2‐butene; and chloroacetaldehyde (20 ± 3%), CH₂O (7 ± 1%), CO₂ (4 ± 1%), and HCOCl (4 ± 1%) from 1‐butene. Product yields from both trans‐2‐butene and 1‐butene were found to be O₂‐dependent. In the case of trans‐2‐butene, the observed O₂‐dependence is the result of a competition between unimolecular decomposition of the CH₃CH(Cl)? CH(O?)? CH₃ radical and its reaction with O₂, with k_decomp/k_O2 = (1.6 ± 0.4) × 10¹⁹ molecule cm^?3. The activation energy for decomposition is estimated at 11.5 ± 1.5 kcal mol^?1. The variation of the product yields with O₂ in the case of 1‐butene results from similar competitive reaction pathways for the two β‐chlorobutoxy radicals involved in the oxidation, ClCH₂CH(O?)CH₂CH₃ and ?OCH₂CHClCH₂CH₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334–353, 2003     

Experimentally determined and calculated values of the energies required to form doubly charged ions of the bromomethanes CH3Br,CH2Br2 and CHBr3

Two experimental techniques were used to determine the double ionization energies of CH₃Br, CH₂Br₂ and CHBr₃. In one, these energies were measured directly by double-charge-transfer spectroscopy. In the other, charge stripping of [CH₃Br]⁺, [CH₂Br₂]⁺ and [CHBr₃]⁺ ions was investigated and the ionization energies of the singly charged ions were measured. The double ionization energies of the molecules obtained by adding known single ionization energies of the molecules to the single ionization energies of the ions were in good agreement with those determined by double-charge-transfer spectroscopy. The relevant mean values from the two techniques were 28.9 ± 0.5, 27.5 ± 0.5 and 29.1 ± 0.5 eV for the double ionization energy of CH₃Br, CH₂Br₂ and CHBr₃, respectively. The results of ab initio calculations using second-order Møller-Plesset perturbation theory were in good agreement with the observed double ionization energies; they were consistently slightly lower than the experimental values.     

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.     

Gas‐phase reactions of Cl atoms with propane,n‐butane,and isobutane

Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl₂ photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm³ molecule^?1 s^?1) have been derived: (7.4 ± 0.2) × 10^?11 exp [‐(70 ± 11)/ T], Cl + C₃H₈ → HCl + CH₃CH₂CH₂; (5.1 ± 0.5) × 10^?11 exp [(104 ± 32)/ T], Cl + C₃H₈ → HCl + CH₃CHCH₃; (7.3 ± 0.2) × 10^?11 exp[?(68 ± 10)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃ CH₂CH₂CH₂; (9.9 ± 2.2) × 10^?11 exp[(106 ± 75)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃CH₂CHCH₃; (13.0 ± 1.8) × 10^?11 exp[?(104 ± 50)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CHCH₃CH₂; (2.9 ± 0.5) × 10^?11 exp[(155 ± 58)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CCH₃CH₃ (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002     

Electrostatic long-range and short-range interactions in linear poly(allylamine hydrochloride) chains

The efficiencies of two azo initiators in the polymerization of allylamine salts in water and organic solvents were compared. The hydrodynamic and molecular characteristics of poly(allylamine hydrochloride) in 0.1 M NaCl in the molecular mass range M×10^?3=18?65 were studied, and the scaling relationships were derived for the intrinsic viscosity ([η]=7.65×10^?3 M ^0.8±0.1), translational diffusion coefficient (D ₀=2.41×10^?4 M ^{?(0.59±0.05)}), and velocity sedimentation coefficient (s ₀=2.77×10^?15 M ^0.41±0.05). The hydrodynamic data were interpreted in terms of electrostatic long-range and short-range interactions. The equilibrium rigidity of poly(allylamine hydrochloride) chains in 0.1 M NaCl and its structural and electrostatic constituents were quantitatively estimated. It was shown that the conformation of poly(allylamine hydrochloride) chains in pure water is close to rodlike.     

The temperature dependence and the mechanism of the SO2 (3B1) quenching reactions

The Arrhenius parameters have been determined for the SO₂(³B₁) quenching reaction (9), SO₂(³B₁) + M → (SO₂ ? M), for 21 different molecules as quenching partner M. The rate constants were calculated from phosphorescence lifetime measurements made over a range of reactant pressures and temperatures. Excitation of the SO₂ (³B₁) molecules was accomplished by two very different methods: (1) a 3829 Å laser pulse generated the triplet directly through absorption within the “forbidden” SO₂ (³B₁) → SO₂ (¹A₁) band; (2) a broadband Xe-flash system generated SO₂(³B₁) molecules and triplets were formed subsequently by intersystem crossing, SO₂(¹B₁) + M → SO₂(³B₁) + M. The measured rate constants were independent of the method of triplet formation employed. For the atmospheric gases, the activation energies (kcal/mole) were identical within the experimental error: N₂, 2.9 ± 0.4; 0₂, 3.2 ± 0.5; Ar, 2.8 ± 0.6; CO₂, 2.8 ± 0.4; CO, 2.7 ± 0.4; CH₄, 2.5 ± 0.6. This energy corresponds to the first region of the SO₂(³B₁) → SO₂(¹A₁) absorption spectra in which Brand and coworkers observe strong perturbations. It is suggested that the quenching in these cases results largely from the physical process involving potential energy surface crossing to another electronic state. Activation energies for SO₂(³B₁) quenching by the paraffinic hydrocarbons show a regular decrease in the series ethane, neopentane, propane, n-butane, cyclohexane, and isobutane, which parallels closely the decrease in C? H bond energies in these compounds. These and other data are most consistent with the dominance of chemical quenching in these cases. The rate constants for the olefinic and aromatic hydrocarbons and nitric oxide show only very small variations with temperature change, and they are near the kinetic collision number. These data support the hypothesis that quenching in these cases is associated with the formation of a charge-transfer complex and subsequent chemical interactions between the SO₂(³B₁) molecule and the π-system of these compounds.     

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.     

N-substituted salicylaldimine complexes of rhodium(III) and related rhodium(III) organometallic derivatives

A series of new Rh^III complexes with N-substituted salicylaldimines have been prepared of the form [RhSBPy₂]PF₆ where SB is a tetradentate N,N′-substituted bis(salicylaldimine) or represents two molecules of a corresponding bidentate derivative. Several of these complexes have been reduced with 0.5% sodium amalgam and the products reacted with CH₃I to yield the organometallic derivatives CH₃RhSBPy.     

Absolute Rate Constants for the Addition of Cyanomethyl (·CH2CN) and (tert-Butoxy)carbonylmethyl (·CH2CO2C(CH3)3) radicals to alkenes in solution

Absolute rate constants and their temperature dependence were determined by time-resolved electron spin resonance for the addition of the radicals ·CH₂CN and ·CH₂CO₂C(CH₃)₃ to a variety of mono- and 1,1-disubstituted and to selected 1,2- and trisubstituted alkenes in acetonitrile solution. To alkenes CH₂?CXY, ·CH₂CN adds at the unsubstituted C-atom with rate constants ranging from 3.3·10³ M ^?1S ^?1 (ethene) to 2.4·10⁶ M ^?1S ^?1 (1,1-diphenylethene) at 278 K, and the frequency factors are in the narrow range of log (A/M ^?1S ^?1) = 8.7 ± 0.3. ·CH₂CO₂C(CH₃)₃ shows a very similar reactivity with rate constants at 296 K ranging from 1.1·10⁴ M ^?1S ^?1 (ethene) to 10⁷ M ^?1S ^?1 (1,1-diphenylethene) and frequency factors log (A/M ^?1S ^?1) = 8.4 ± 0.1. For both radicals, the rate constants and the activation energies for addition to CH₂?CXY correlate well with the overall reaction enthalpy. In contrast to the expectation of an electro- or ambiphilic behavior, polar alkene-substituent effects are not clearly expressed, but some deviations from the enthalpy correlations point to a weak electrophilicity of the radicals. The rate constants for the addition to 1,2- and to trisubstituted alkenes reveal additional steric substituent effects. Self-termination rate data for the title radicals and spectral properties of their adducts to the alkenes are also given.     

Kinetics of the reactions of OH radicals with n-alkanes at 299 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of n-alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1s^?1, the rate constants obtained are (X10¹² cm³ molecule^?1 s^?1): propane 1.22 ± 0.05, n-pentane 4.13 ± 0.08, n-heptane 7.30 ± 0.17, n-octane 9.01 ± 0.19, n-nonane 10.7 ± 0.4, and n-decane 11.4 ± 0.6. The data for propane, n-pentane, and n-octane are in good agreement with literature values, while those for n-heptane, n-nonane, and n-decane are reported for the first time. These data show that the rate constant per secondary C—H bond is ∽40% higher for —CH₂— groups bonded to two other —CH₂— groups than for those bonded to a —CH₂— group and a —CH₃ group.     

Electronic Effects in X(CH2)nY Homologous Series by NMR and Quantum Chemistry

The ^79,81Br NQR spectra of compounds of the Br(CH₂) _n COOH (n = 1-5) and Br(CH₂) _n COOSi·(CH₃)₃ (n = 1, 2, 4, 5) homologous series were measured at 77 K. The NQR frequencies of compounds of the first series as n increases to 3 and then oscillate. The ³⁵Cl NQR frequencies of Cl(CH₂) _n Cl series molecules, estimated from the Cl3p populations resulting from RHF/6-31G(d) calculations, steadily decrease as n increases from 1 to 10. No oscillation of calculated ³⁵Cl frequencies was revealed for compounds of the latter series (by contrast to experimental observations). The calculation results give no way to deducing the mechanism of the oscillation effect.     

Temperature‐dependent rate coefficient measurements for the reaction of bromine atoms with a series of aldehydes

Relative rate coefficient data have been obtained for the reactions Br + RCHO → RCO + HBr for a series of aldehydes: HCHO, reaction (1); CH₃CHO, reaction (2); CH₃CH₂CHO, reaction (3); CH₃CH₂CH₂CHO, reaction (4). Measurements were made over the temperature range 240–300 K in an environmental chamber/FTIR spectrometer system, using standard relative rate techniques. All measured rate coefficient ratios were found to be independent of temperature over the range studied (k₂/k₁ = 3.60 ± 0.29, k₃/k₁ = 6.65 ± 0.53, k₄/k₁ = 8.62 ± 0.69, and k₃/k₂ = 1.80 ± 0.14), implying that the activation barriers for all four reactions are essentially identical with the A‐factors increasing with the size of the aldehyde. Relative rate coefficients for k₁ and k₂ agree well with currently recommended data at room temperature, but inconsistencies on the order of 20% arise at lower temperatures. The entire set of relative rate coefficient measurements is put on an absolute scale using a combination of currently recommended values for k₁ and k₂. The following expressions (all in units of cm³ molecule⁻¹ s⁻¹) are obtained: k₁ = (0.79 ± 0.10) × 10⁻¹¹ exp(−580 ± 200/T), k₂ = (2.7 ± 0.4) × 10⁻¹¹ exp(−567 ± 200/T), k₃ = (5.75 ± 0.75) × 10⁻¹¹ exp(−610 ± 200/T), k₄ = (5.75 ± 0.75) × 10⁻¹¹ exp(−540 ± 200/T), where uncertainties quoted for the A‐factor reflect the uncertainty in the room temperature value. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 460–465, 2000     

Deactivation of I(2P1/2) by CH3Cl,CH2Cl2, CHCl3, CCl3F,and CCl4

Collisional deactivation of I(²P_1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH₃Cl, CH₂Cl₂, CHCl₃, CCl₃F, and CCl₄ are 3.1±0.3×10⁻¹³, 1.28±0.08×10⁻¹³, 5.7±0.3×10⁻¹⁴, 3.9±0.4×10⁻¹⁵, and 2.3±0.3×10⁻¹⁵cm³ molecule⁻¹ s⁻¹, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH₃Cl, CH₂Cl₂, and CHCl₃ reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm⁻¹) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998     

The ultraviolet absorption spectra of the acetyl radical and the kinetics of the CH3 + CO reaction at room temperature

A continuum-absorption spectrum between 200 and 240 nm is assigned to the acetyl radical. Kinetic measurements using molecular modulation spectroscopy show for the reaction CH₃ + CO (+M) → CH₃CO + M the rate constants are (1.8 ± 0.2) × 10^?18 cm³ molecule^?1 s^?1 at 100 Torr and (6 ± 1) × 10^?18 at 750 Torr. The rate constant for acetyl combination 2CH₃CO → (CH₃CO)₂ is (3.0 ± 10) × 10^?11 at 25°C.     

Hydrodynamic and molecular characteristics of graft copolymers of chitosan with acrylamide

The conformational properties of macromolecules of chitosan and its copolymers with acrylamide in a mixed solvent 0.33 M CH₃COOH + 0.3 M NaCl have been investigated by means of translation diffusion and viscometry. The copolymer macromolecules in a solvent suppressing polyelectrolyte effects possess a higher intracoil density (ρ_av = 0.010 g/cm³) than the chitosan macromolecules (ρ_av = 0.006 g/cm³), even though the hydrodynamic radius R _h of chitosan is smaller by a factor of ～1.5.     

Atmospheric chemistry of n‐CH3(CH2)xCN (x = 0–3): Kinetics and mechanisms

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of n‐CH₃(CH₂)_xCN (x = 0–3) with Cl atoms and OH radicals: k(CH₃CN + Cl) = (1.04 ± 0.25) × 10⁻¹⁴, k(CH₃CH₂CN + Cl) = (9.20 ± 3.95) × 10⁻¹³, k(CH₃(CH₂)₂CN + Cl) = (2.03 ± 0.23) × 10⁻¹¹, k(CH₃(CH₂)₃CN + Cl) = (6.70 ± 0.67) × 10⁻¹¹, k(CH₃CN + OH) = (4.07 ± 1.21) × 10⁻¹⁴, k(CH₃CH₂CN + OH) = (1.24 ± 0.27) × 10⁻¹³, k(CH₃(CH₂)₂CN + OH) = (4.63 ± 0.99) × 10⁻¹³, and k(CH₃(CH₂)₃CN + OH) = (1.58 ± 0.38) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ at a total pressure of 700 Torr of air or N₂ diluents at 296 ± 2 K. The atmospheric oxidation of alkyl nitriles proceeds through hydrogen abstraction leading to several carbonyl containing primary oxidation products. HC(O)CN, NCC(O)OONO₂, ClC(O)OONO₂, and HCN were identified as the main oxidation products from CH₃CN, whereas CH₃CH₂CN gives the products HC(O)CN, CH₃C(O)CN, NCC(O)OONO₂, and HCN. The oxidation of n‐CH₃(CH₂)_xCN (x = 2–3) leads to a range of oxygenated primary products. Based on the measured OH radical rate constants, the atmospheric lifetimes of n‐CH₃(CH₂)_xCN (x = 0–3) were estimated to be 284, 93, 25, and 7 days for x = 0,1, 2, and 3, respectively.     

Molecule/radical reactions prior to ionization under negative chemical ionization conditions

It is shown that alkyl radical species present in CH₄ or iso-C₄H₁₀ plasma can react with substrate molecules to give [M+C_nH_2n] species. These species become evident especially in negative chemical ionization as [M+C_nH_2n]^?˙ and, less obviously, in positive chemical ionization as [M+C_nH_2n+1]⁺ ions which, for example in natural products chemistry, may be mistaken for a series of homologous compounds present in the sample.