Rate coefficients for the reactions of hydrogen atoms with 1-bromopropane, 2-bromopropane, 1-bromobutane,and 2-bromobutane

The rate coefficients for the reactions of hydrogen atoms with n-C₃H₇Br, s-C₃H₇Br, n-C₄H₉Br, and s-C₄H₉Br were determined in a discharge flow-reactor at 298 K and a pressure of 4 mbar. Molecular-beam sampling and subsequent mass-spectrometric detection with electron-impact ionisation was used for the measurement of the bromo-hydrocarbon concentration. The rate coefficients obtained are (in 10¹⁰ cm³ mol⁻¹ s⁻¹): 2.3±1.2 for n-C₃H₇Br, 2.3±1.2 for s-C₃H₇Br, 2.4±1.2 for n-C₄H₉Br, and 2.8±1.4 for s-C₄H₉Br. The results are compared with predictions from bond-energy bond-order (BEBO) calculations, where a reasonable agreement is found. Furthermore, also by BEBO calculations, the relative importance of bromine abstraction as compared to hydrogen abstraction is estimated. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 721–727, 1998     

Temperature dependence of the relative rate constants of the reactions of alkanes with oh radicals in aqueous solution

A study was carried out on the rate constant ratio (k _RH/k _EtH) in reactions of alkanes C₃H₈, n-C₄H₁₀, n-C₅H₁₂, n-C₆H₁₄, i-C₄H₁₀, c-C₅H₁₀, and c-C₆H₁₂ with OH radicals in water at 5-55°C and the relative activation parameters A _RH/A _EtH and E _EtH – E _RH. The values of E _EtH – E _RH in water and the gas phase have opposite signs. The values of k _RH/k _EtH decrease with increasing temperature in the gas phase but increase in water. The behavior of these reactions in water may be attributed to a solvent cage effect.     

13C n.m.r. studies of organosilanes: II—substituent chemical shift parameters for alkoxysilanes

The ¹³C n.m.r. spectra of forty alkoxysilanes of the general type X_nSi(OR)_4–n (X = CH₃, C₆H₅, H; R = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, s-C₄H₉, n-C₅H₁₁, CH(CH₃)(C₆H₅), C₆H₅) have been recorded and assigned. The chemical shifts of the α-carbon resonances of the alkoxy groups are shown to depend on both the nature of the alkoxy group and the number and type of substituents on the silicon. Regression analyses of the data give empirical substituent chemical shift (SCS) parameters for the silyl substituents. The β-carbon resonances are shown to be dependent on the presence of the silyl group, but not the specific silyl substituents.     

Prediction of activity coefficients and Henry's constants at infinite dilution for mixtures of n-alkanes

Trejo Rodríguez, A. and Patterson, D., 1984. Prediction of activity coefficients and Henry's constants at infinite dilution for mixtures of n-alkanes. Fluid Phase Equilibria, 17: 265–279.The corresponding-states principle (CSP) for chain molecules has been used to predict activity coefficients γ_i^∞ at infinite dilution and Henry's constants H_i,j for mixtures of n-alkanes. The mixtures for which predictions of γ_i^∞ are made include n-C₄ through n-C₁₀ as the solute in several pure higher n-alkanes, at several temperatures from 30 to 90°C. Predictions of H_i,j are made for mixtures where the solute is C₂ through n-C₈ and the solvent any n-alkane from n-C₄ through n-C₂₂, also at several temperatures, from –15 to 177°C. The predicted values are compared with experimental data from the literature, and in all cases the agreement is remarkably good. The temperature dependence of H_i,j for some mixtures is used to derive heats of solution ΔH_s, and comparison is again carried out with available experimental values.     

Phytochemical Study on Moghania Strobilifera

n-C₂₆H₅₄, n-C₂₇H₅₆, n-C₂₈H₅₈, n-C₂₉H₆₀, n-C₃₀H₆₂, n-C₃₁H₆₄, n-C₃₂H₆₆, n-C₃₃H₆₈, stigmasterol, β-sitosterol and two unidentified compounds: a saturated ester (mp 79-81°C); an unsaturated alcohol (mp 87-88°C) were isolated from the whole herb of Moghania strotilifera.     

Evaluated and estimated kinetic data for phase reactions of the hydroperoxyl radical

Methods are discussed for the production and detection of the hydroperoxyl radical for use in gas phase kinetic studies. Rate constants for gas phase reactions of the hydroperoxyl radical with itself, H₂, H₂O, CO, NO, SO₂, O₃, C₂H₆, C₃H₈, i-and n-C₄H₁₀, C₂H₄, i-C₄H₈, HCHO, C₂H₅CHO, n-C₃H₇CHO, Br, O, OH, and H are critically evaluated. Recommended or estimated rate constant expressions with associated error limits are given applicable over specified temperature ranges (normally 300–1000°K). The reactivity of HO₂ compared with OH, O, H, F, Cl, Br, CH₃, and CH₃O is presented in tabular form and the implications for atmospheric chemistry are discussed.     

Thermodynamic interactions in rubbery polymer/gas systems

The Flory–Huggins interaction parameters χ for 23 gases (He, Ne, Ar, Kr, Xe, H₂, N₂, O₂, N₂O, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, 1,3-C₄H₆, four C₄H₈'s, n-C₄H₁₀, iso-C₄H₁₀, and n-C₅H₁₂) in five rubbery polymers (1,2-polybutadiene (PB), poly(ethylene-co-vinyl acetate)) (EVAc), polyethylene (PE), polypropylene (PP), and poly(dimethyl siloxane) (PDMS) were determined from either literature data on Henry's law coefficient and partial molar volume or those on sorptive dilation for each polymer/gas system. Values of χ for the gases increased in the order of PDMS < PP ≡ PB < EVAc ≡ PE. Among the gases except He and H₂ whose χ values are not reliable, Ne and Xe have respectively the highest and the lowest values of χ for the polyolefins. The χ values of the hydrocarbons were compared together with previously reported χ values of n-alkanes C₃-C₁₀. The dependencies of χ upon concentration and temperature were discussed on the basis of the literature data. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1049–1053, 1997     

The use of transition-state theory to extrapolate rate coefficients for reactions of oh with alkanes

A method is described for extrapolating existing experimental data on the reactions of OH radicals with alkanes to higher temperatures using conventional transition-state theory. Expressions are developed for the estimation of the structural properties of the activated complex necessary for calculating ΔS^± and ΔH^±. The vibrational frequencies and internal rotations of the activated complex are given by those of the reacting alkane or the analogous alcohol and a set of additional internal modes that is the same for all OH + alkane reactions considered. Differences between primary, secondary, and tertiary hydrogen attack are discussed, and the validity of representing the activated complexes of all OH + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Calculations are presented for the reaction of OH with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, i-C₄H₁₀, c-C₄H₈, c-C₅H₁₀, c-C₆H₁₂, (CH₃)₂CHCH(CH₃)₂, (CH₃)₃CCH(CH₃)₂, (CH₃)₄C, and (CH₃)₃CC(CH₃)₃, and the results are compared with experiments.     

Study on ketalization reaction of poly(vinyl alcohol) by ketones. VIII. kinetic study on acetalization and ketalization reactions of poly(vinyl alcohol)

The kninetics of acid-catalyzed acetalization and ketalization of poly(vinyl alcohol) (PVA) were systematically studied in completely homogeneous media with carefully selected solvents. Thus the acetalization reaction was run in water with six aldehydes [R₁CHO (R₁ = H, CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, ClCH₂)], whereas the ketalization in dimethylslfoxide with 11 ketones [R₂CH₃CO (R₂ = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, tert-C₄H₉, C₆H₅CH₂, C₆H₅CH₂CH₂), cyclopentanone, and cyclohexanone]. The latter was difficult to proceed in aqueous media. Both reactions were reversible and bimolecular and, despite the use of different solvents, gave similar heats of reaction (7.5 kcal/mol) and activation energies (ca. 15 kcal/mol) except for the case of formaldehyde and chloroacetaldehyde; however the equilibrium constants at 25°C showed that the acetalization is thermodynamically much more favored than the ketalization (ca. 5000 vs. 0.01–0.9), probably because of steric hindrance of the ketone substrate. The rate constants of hydrolysis (reverse reactions) for the poly(vinyl acetal) and poly(vinyl ketal) followed the Hammett-Taft equation to give a single p* (=3.60) that is very close to that for the hydrolysis of diethyl acetal and ketal. From these and other data, it was concluded that the polymer hydrolysis, as well as PVA acetalization and ketalization, are all electrophilic reaction where the formation of hemiacetal or hemiketal is the rate-determining step. © 1996 John Wiley & Sons, Inc.     

The Kinetics of alkyl radical reactions with aliphatic alcohol glasses as studied by electron spin resonance

Methyl radical reactions with matrix molecules in glasses C₂H₅OH, (CH₂OH)₂, n- and i-C₃H₇OH, n- and i-C₄H₉OH, n- and i-C₅H₁₁OH, C₂D₅OH, and i-C₃D₇OD, and the reactions of ?₂H₅, ?₃H₇, ?₄H₉, ?₅H₁₁ with methanol glasses have been studied. Alkyl radicals were produced by photolysis of diphenylamine–alkylhalide–alcohol mixtures using ultraviolet light. In all cases the alkyl radical decay follows the law c = c₀ exp(-k √t). The √t law should not be associated with alkyl radical diffusion in a matrix. A method of processing the kinetics of those reactions in which one paramagnetic species changes into another with the total concentration being constant and the electron spin resonance spectra of both species overlapping, is described.     

Polyterephthalates of 2,3-disubstituted butanediols-1,4: Effect of aliphatic substituents on Tg and Tm of the polyesters

Poly(2,3-dialkylbutanediol-1,4 terephthalates) with the alkyl substituents CH₃, C₂H₅, n-C₃H₇, iso-C₃H₇, n-C₄H₉, and n-C₁₀H₂₁, andn-C₁₆H₃₃ were synthesized from the corresponding 2,3-dialkylbutanediols-1,4 and dimethyl terephthalate or terephthaloyl chloride. The substituents of the butanediol-1,4 portion of the polyterephthalates influence the ¹³C NMR chemical shifts of the carbon atoms near the branching site, the glass transition (T_g), and the crystallizability. Small alkyl substituents do not change the T_g of the polymers, whereas bulky substituents such as the isopropyl group increase the T_g and long normal alkyl groups as substituents decrease the T_g of the polymers. Crystallinity in these polyterephthalates was found only with CH₃ and C₁₆H₃₃ as the 2,3-dialkyl substituents in the butanediol-1,4 portion of the polyester. This crystallinity of polyterephthalate of 2,3-di-C₁₆H₃₃ substituted butanediol-1,4 could be assigned to side-chain crystallization of the paraffinic groups.     

Kinetic Analysis of the Thermal Decomposition of Dialkyldithiocarbamates Chelates of Indium(III)

The kinetics of thermal decomposition of solid In(S₂CNR₂)₃ complexes, (R=CH₃, C₂H₅, n-C₃H₇,i-C₃H₇, n-C₄H₉ and i-C₄H₉), has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions occur in the liquid phase, except for the In(S₂CNMe₂)₃ and In(S₂CNPrⁱ ₂)₃ compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic modeling of the reactions of C3H3+ with acetylene,deuteroacetylene, and diacetylene

The reactions of ?-C₃H₃⁺ (propargylium cation) with acetylene and diacetylene have been modeled kinetically. Data were obtained from Fourier Transform Ion Cyclotron Resonance (FTICR) experiments on these systems, which are themselves models for soot particle initiation. Acetylene forms an encounter complex with ?-C₃H₃⁺, but, in the absence of a third body collision, the complex decomposes to acetylene and c-C₃H₃⁺ (cyclopropenylium cation) at about 1/3 the rate it decomposes to acetylene and ?-C₃H₃⁺, in spite of the fact that c-C₃H₃⁺ is ca. 115 kJ/mol more stable than ?-C₃H₃⁺. The encounter complex is long enough lived, and energetic enough, to scramble deuterium in reactions between ?-C₃H₃⁺ and C₂D₂. These reactions have been successfully modeled, yielding a nearly statistical distribution of deuterium, and a rather large kinetic isotope effect. The more complex reactions of ?-C₃H₃⁺ with diacetylene have also been modeled.     

Quenching of *UF6 (A state) by alkanes

The removal of *UF₆ (A state) molecules by selected alkanes has been investigated at 25°C. The following rate constants (units of 10¹¹ l/mol·sec) were evaluated: iso-C₄F₁₀, 0.0432 ± 0.0115; n-C₄F₁₀, 0.0764 ± 0.020; C₂F₆, 0.0192 ± 0.0052; CH₄, 0.0612 ± 0.0061; C₂H₆, 3.78 ± 0.60; C₃H₈, 5.08 ± 0.60; n-C₄H₁₀, 5.05 ± 0.78; iso-C₄H₁₀, 4.17 ± 1.15; neo-C₅H₁₂, 6.59 ± 0.93; CF₃? CH₃, 0.0385 ± 0.0056; CF₂H? CF₂H, 0.0729 ± 0.0074; and CF₂H? CFH₂, 0.149 ± 0.015. The perfluoro-alkane quenching of *UF₆ proceeds via a physical mechanism. The other alkane quenching reactions are consistent with a chemical mechanism also contributing in varying degrees which may involve removal of two hydrogens from the alkane.     

Low-frequency Raman-active vibrations of triclinic n-paraffins

The low-frequency Raman spectra of triclinic n-paraffins, n-C₈H₁₈ through n-C₂₄H₅₀, were observed. The normal-coordinate treatments of crystal vibrations of n-C₈H₁₈ through n-C₁₈H₃₈ were carried out. Six characteristic series of the observed Raman lines were assigned to rotatory lattice vibrations and intramolecular skeletal vibrations.     

Kinetic and thermodynamic parameters of the thermal decomposition of zinc(ii) dialkyldithiocarbamate complexes

The thermodynamic and kinetic parameters of the thermal decomposition of Zn(S₂CNR₂)₂ complexes (R=CH₃, C₂H₅ and n-C₃H₇) were determined with the dynamic thermogravimetric method. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions for chelates with R=C₂H₅ and n-C₃H₇ occur in the liquid phase, at temperatures far away from their melting points, whereas for the complex with R=CH₃ the thermal decomposition begins at a temperature closer to its melting point, suggesting a rather complex decomposition mechanism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Polymerization of 1-methylthio-1-alkynes and polymer properties

Polymerization of 1-methylthio-1-alkynes (MeSC?CR; R = Et, n-Bu, n-C₆H₁₃, and n-C₈H₁₇) was studied by use of transition metal catalysts. A 1 : 2 mixture of MoCl₅ and Ph₃SiH provided polymers having M?_w over 1 × 10⁵ in 30–50% yields from these monomers. The length of the alkyl group hardly affected the polymerization. The monomer, MeSC?C-n-C₆H₁₃, showed low reactivity in homopolymerization, but higher reactivity than that of MeC?C-n-C₅H₁₁ in copolymerization. Poly(1-methylthio-1-alkyne)s were colorless solids, and those with long alkyl pendants (R = n-C₆H₁₃, n-C₈H₁₇) were soluble in various organic solvents. The present polymers were thermally more stable than poly(2-alkyne)s, the corresponding hydrocarbon polymers.     

Structure and properties of 1,2-, 1,7-, and 1,12-dicarba-closo-dodecaboranes(12): A quantum chemical study

The molecular and electronic structures and thermodynamic parameters of 1,2-, 1,7-, and 1,12-dicarba-closo-dodecaborane(12) molecules in the singlet ground state were calculated by the Hartree-Fock, DFT, and MP2 (including B3LYP/6-311G(2d,2p) and MP2/6-311+G(d,2p) methods). The energies and character of spatial localization of the frontier MOs in o-, m-, p-carboranes(12) correlate with the changes in the configuration stabilities and reactivities in the reactions of carboranes with electrophilic and nucleophilic agents and bases. The electrostatic potential distributions in the molecules and the atomic charge distribution of hydrogen atoms correlate with the known chemical properties of carboranes(12). The thermodynamic parameters of two isomerization reactions, o-C₂B₁₀H₁₂ ⇌ m-C₂B₁₀H₁₂ and m-C₂B₁₀H₁₂ ⇌ p-C₂B₁₀H₁₂, calculated for the temperature range 298–1000 K agree with experimental data within the limits of measuring error. The values of the electron density and the Laplacian of the electron density at the (3, −1) critical points of the B-H and C-H bonds correlate with the reactivities of the title compounds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2074–2080, December, 2006.     

Solid-state chlorodecarboxylation of mono- and dicarboxylic acids with the Pb(OAc)<Subscript>4</Subscript>-MCl system

Solid state reactions of acids RCOOH (R = n-C₇H₁₅, BuC(Et)H, n-C₉H₁₉, PhCH₂, PhCH₂CH₂, H₂C=CH(CH₂)₈, or MeOOC(CH₂)₃) with Pb(OAc)₄ combined with KCl, NaCl, CdCl₂, or NH₄Cl in the absence of a solvent and without mechanical activation afford chlorohydrocarbons RCl. The corresponding reactions of acids HOOC(CH₂)_nCOOH (n = 3–6) give dichloroalkanes Cl(CH₂)_nCl and γ-butyrolactone (n = 3).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2105–2109, October, 2004.     

Copolymers of Maleic Anhydride and Methylene Alkanes: Synthesis,Modification, and Pour Point Depressant Properties

Copolymers with the equimolar composition and presumably alternating microstructure are synthesized by the radical copolymerization of methylene alkanes, the products of dimerization of α-olefins with the general formula RCH₂CH₂C(=CH₂)R (R = n-C₄H₇, n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅), with maleic anhydride. The products of reactions between the obtained copolymers and 1-octadecanamine or 1-octadecanol are isolated and spectrally characterized. The depressor efficiency of the copolymers with respect to the solutions of paraffins in n-alkanes is studied. Qualitative differences between the copolymers of maleic anhydride with methylene alkanes and reference copolymers based on 1-octadecene are estimated using vibrational viscometry combined with analysis of the size and morphology of paraffin crystals. It is shown that the copolymers with methylene alkanes more effectively decrease the cold filter plugging point (CFPP) of paraffin solutions in n-decane.