Absolute rate constant for the reaction of Phenyl radical with Acetylene

The absolute rate constant for the reaction of phenyl radical with acetylene has been measured at 20 torr total pressure in the temperature range of 297 to 523 K using the cavity-ring-down technique. These new kinetic data could be quantitatively correlated with the data obtained earlier with a relative rate method under low-pressure (10^?3–10^?2 torr) and high-temperature (1000–1330 K) conditions. These kinetic data were analyzed in terms of the RRKM theory employing the thermochemical and molecular structure data computed with the BAC-MP4 technique. The calculated results reveal that the total rate constant for the C₆H₅ + C₂H₂ reaction (k_t) is pressure-independent, whereas those for the formation of C₆H₅C₂H (k_b) and the C₆H₅C₂H₂ adduct (k_c) are strongly pressure-dependent. A least-squares analysis of the calculated values for 300–2000 K at the atmospheric pressure of N₂ or Ar can be given by and all in units of cm³/s. The latter equation effectively represents the two sets of experimental data. © 1994 John Wiley & Sons, Inc.     

The reaction of O(3P) with C2HCl3

The reaction of O(³P), prepared from the Hg photosensitization of N₂O, with C₂HCl₃ was studied at 25°C. The products of the reaction in the absence of O₂ were CO, CHCl₃, and polymer (as well as N₂ from the N₂O). The quantum yields of CO and CHCl₃ were 0.23 ± 0.01 and 0.14 ± 0.05, is respectively independent of reaction conditions. The reaction mechanism is with k_14a/k₁₄ = 0.23, where k_14a + k_14b. Most of the HCl and CCl₂ combine to form CHCl₃, but some other products must also be formed to account for the difference in the CO and CHCl₃ quantum yields. The C₂HCl₃O* adduct polymerizes without involving additional C₂HCl₃ molecules, since the quantum yield of C₂HCl₃ disappearance, ? Φ{C₂HCl₃}, was about 1.0 at high values of [N₂O]/[C₂HCl₃]. The rate coefficient for the reaction of O(³P) with C₂HCl₃ is 0.10 that for the reaction of O(³P) with C₂F₄. In the presence of O₂ the free radical chain oxidation occurs because of the reaction The main product is CHCl₂CCl(O) with smaller amounts of CO and CCl₂O, and some CO₂. The chain lengths were long and values of ? Φ {C₂HCl₃} up to 90 were observed.     

High‐temperature reaction of C2 with NO including product channel measurements

The reaction of C₂ radicals with NO was studied behind reflected shock waves in the temperature range 3150 K≤T≤3950 K. The shock‐induced pyrolysis of acetylene, highly diluted in argon, was used as a well defined source for C₂ radicals, which were detected by ring‐dye‐laser absorption spectroscopy (RDLAS) at 516.646 nm. The perturbation of the C₂ by the addition of NO to the initial mixtures results in a fast removal of the C₂ radicals, which is mainly caused by the reaction: ((R5)) for which the overall rate coefficient was obtained. The product channels of this reaction were studied by additional measurements of O‐atoms, N‐atoms, and CN radicals. O and N were detected using atomic resonance absorption spectroscopy (ARAS) and the CN radicals were followed by their emission using a spectrograph and an intensified CCD‐camera. The reactions leading to the product channels C₂N+O (R5a) and to C₂O+N (R5b) were identified as the main channels with a branching ratio of k_5a/k₅=70% and k_5b/k₅=30%, while the channel leading to CN+CO (R5c) was found to be neglectable. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 11–21, 1999     

Thermal stability of intermediate sized acetylenic compounds and the heats of formation of propargyl radicals

4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are In combination with previous results, rate expressions for propargyl C? C bond cleavage are related to that for the alkanes by the expression These results yield a propargyl resonance energy of D(nC₃H₇-H) – D(C₃H₃-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH₃C≡CCH₂-H) – D(C₃H₃-H) = 0.6 ± 3 kJ, D(sC₄H₉-H) – D(iC₃H₇-H) = 0 ± 3 kJ, D(iC₄H₉-H) – D(nC₃H₇-H) = 2 ± 3 kJ, and D(nC₃H₇-H) – D(iC₃H₇-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.     

新型尾式卟啉的合成及与人血清白蛋白的相互作用

合成了未见文献报道烟酸分子修饰的自由卟啉o-(niacin)C4O-TPP、p-(niacin)C4O-TPP及锌配合物o-(niacin)C4O-TPPZn、p-(niacin)C4O-TPPZn。通过元素分析、紫外-可见光谱、核磁共振氢谱、红外光谱等多种谱图对结构进行了表征。为模拟金属卟啉的生物功能,采用荧光光谱滴定法测定了金属锌卟啉与人血清白蛋白(HSA)相互作用的光谱性质。按照Stern-Volmer方程、Lineweaver-Burk双倒数方程分析和处理试验数据,得到了反应的猝灭常数、结合常数和热力学参数等。实验结果表明:锌卟啉与人血清白蛋白之间发生了较强的静态荧光猝灭效应,二者之间是以氢键或Van der Waals力结合反应。     

Chain transfer in ethylene polymerization. VII. Very reactive and depletable transfer agents

The study of chain transfer in the free-radical polymerization of ethylene was extended to very reactive transfer agents, particularly aldehydes and mercaptans The chaintransfer constant C_s for aldehydes was insensitive to temperature changes but was strongly reduced as pressure was increased. Mercaptans were found to deplete during polymerization (C_s > 1.0). The conventional Mayo equation was integrated to allow accurate calculation of C_s for depleting transfer agents.     

Simplified treatment of cooligomerization kinetics

Equations for the degree of polymerization and the cooligomer composition in the styrene (A)–methyl methacrylate (B)–CCl₄(S) system were derived from the assumed reaction scheme by the use of some assumptions for simplification, and their appropriateness was examined. The chain transfer constants of the growing radicals of styrene (C_SA) and methyl methacrylate (C_SB) to CCl₄, which were estimated from the apparent chain transfer constants C_SAB in the cooligomerization system, agreed with the homooligomerization values. This means that the degree of the polymerization of the cooligomer can be expressed by the equation: where P_n is the degree of polymerization of the cooligomer and P_nO is that when no chain transfer agent (CCl₄) is added; r_A and r_B are the monomer reactivity ratios of monomers A and B in this system. The cooligomer composition deviated from the statistical steady-state composition on the low molecular weight side, and this deviation was explained by the equation:      

The kinetics of radiation induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclanes

The kinetics of gamma-radiation induced free radicals reactions in carbon tetrachloride solutions of cyclohexane, cyclooctane and cyclododecane were studied in the range of 27–190°C. The activation energies found were in the order c? C₆H₁₂ > c? C₁₂H₂₄ > c? C₈H₁₆, which was explained as due to their ring strain which has the same order. The following log k₁ was obtained using the known Arrhenius parameters for CCl₃ radical recombination:      

Crosslinking,filler, or transition constraint of polymer networks. II

The theory of Part I is developed by application to filler reinforcement of NR and SBR. For unswollen but prestretched networks it quantifies entire stress–strain curves and applies new concepts of extensibility and strain hardening. Constraint of swelling is expressed by a constant φ, termed linkage reinforcement, and by an effective hard fraction C_h per cubic centimeter of compound. For rubber–filler swelling v_c the modified Flory functions F(v_c) in part 1 need 3% correction. Then, relative to gum fix points 1/F₀(v_r): where C_h ≤ 1.15C for filler concentrations C per cubic centimeter of compound. The effective C_h comprises the volume fraction C* of bonded particles and 5–10 Å of surface–bound rubber that has been stretched hard by swelling. When needed, the actual crosslink density and intrinsic linkage reinforcement φ₀ can be obtained by dividing by (1 + 2.5C_φ) where C_φ = (C ln φ)/(1 + 2.5C). The case C_h ≤ 1.15C with Graphon or inert fillers is identified and assessed by equations: Results C_h > 1.15C are invalid, but then C_h ≈ 1.15C* ≈ 1.15C, e.g., for carbon blacks. Even Graphon is distinguished from inert fillers at low concentrations C by substantial constraint reinforcement F₀(v_r)/F(v_c) > 1. For prestressed dry rubber a modulus G, network extensibility α_b ? 1, and upturn coefficient μ_h express the whole curve; G and μ_h show identical constraint strength distributions. Network extensibility α_b ? 1 is the microbreaking strain (prestretch); for pure elastomer it is elongation at break. The relation of stress F to extension ratio α is: where C₂* = 0.7 and j = 0.4 from NR/MPC data. Strain-hardening coefficients h are obtained from μ_h by the theory given in Part I. Hard modulus components G_h = 0.7 ln (h/h₀) vanish as h → h₀ (gum) = 110. After high prestresses the residual ln-(h^*/h₀) due to strong carbon-rubber linkages implies G_h* = 0.42 kg/cm², i.e., ca. 10% of the normal cure crosslinks.     

The reaction of 2,5-dimethylpyrrole with O2(a1Δg) in the gas phase

The chemical reaction of 2,5-dimethylpyrrole (C₆H₉N) with O₂(¹Δ_g) was studied in the gas phase in an isothermal flow reactor at room temperature and low pressures. The C₆H₉N concentration profiles were studied under pseudo-first order conditions [C₆H₉N]_° ? [O₂(¹Δ_g)] with mass-spectrometric detection of C₆H₉N. O₂(¹Δ_g) was produced either in a microwave discharge or in a chemical reaction. The value for the rate constant: was measured. The rate constant is compared to the value obtained for the quenching process. The primary product C₆H₉NO₂ was detected by mass spectrometry and the reaction mechanism is proposed. The possibility of using this reaction as a gas phase titration reaction for O₂(¹Δ_g) is discussed.     

The reactions of C2F5 radicals with benzene in the vapor phase

C₂F₅ radicals were generated in the presence of benzene vapor by the reaction The radicals react with the benzene by addition and pseudo H abstraction The rate constant k_add for the addition reaction (7) is given by where θ = 2.303RT cal/mole and k_c is the rate constant for combination of C₂F₅ radicals. The addition becomes reversible above 110°C. The reactions of CF₃ and C₂F₅ radicals with benzene vapor are compared.     

Determination of D[C6F5-I] by the toluene carrier method

The pyrolysis of C₆F₅I has been studied by the toluene carrier method over the temperature range of 900–978°K with contact times of 0.4–2.0 seconds and total pressures of 11.2–19.5 torr. Percent decomposition ranged from 8.6 to 97.7%. With toluene-to-C₆F₅I molar ratios of greater than 150, 85–100% of the C₆F₅ released abstracts a hydrogen atom from toluene to produce C₆F₅H. No significant quantities of I₂ were observed and the only major gaseous product was HI. Within the limits of the experimental method the decomposition of C₆F₅I was first order and homogeneous. Least squares analysis of log k₁ and 10³/T(C₆F₅I → C₆F₅ + I) values gives while a weighted line of best fit yields. Based on this latter equation D[C₆F₅? I] at 298°K is estimated as 66.2 kcal/mole.     

Crosslinking,filler, or transition constraint of polymer networks. I

The basic theory of modulus/swelling is developed to allow for limited extensibility, filler reinforcement or transition effects, and steric hindrance of aligned segments by extended chains or filler particles. Filler forms an effective hard fraction C_h per cubic centimeter of compound with v_c a new (compound) index of swelling. For 1/M_c + σ fix points having ratio φ to gum values 1/F₀(v_r) and with F(v_c) replacing the Flory function F(v_r): where σ denotes entanglement. Linkage reinforcement φ does not vary with sulfur crosslinking of SBR. Vacuoles invalidate φ from mass-increment F₀(v_r)/F(v_r) for inert fillers. Then, or for Graphon, with negligible φ ≈ 1: The effective C_h includes rubber stretched hard on Graphon by swelling or trapped inside hard aggregates. Only the right-hand equation fits normal blacks. In theory, C_h can always be obtained from swollen moduli G by linear slopes (1 + 1.4C_h) relating F(v_c) and (1 ? C)ρRT/G. For filler fractions C ≥ 0 cm^?3 and low strains α = 1.5?2.0 below prestretch the modulus G is given a new basic definition: Here C₂* ≈ 0.7 corresponds to Mooney-Rivlin C₂ and the effective crosslinking 1/[M_c] = (ρRT)^?1G is equal to (1 ? C)(1/M_c + σ) for unswollen prestretched rubber (v_r = 1). For higher strains a hypothesis of strain hardening is proposed. This is distinct and opposite in character to the initial prestretch softening (Mullins effect). Nonlinear effects of crosslinks are expressed by a fractional stress-upturn Ω (1/M_c + σ), effective mesh wieght (1/M_c + σ)^?1 ? Ω, and hard fraction Ω(1/M_c + σ). For μ_h characterizing strain hardening up to the prestretch (α_h ? 1) their contribution is: The sixth-power refinement has J = j(α_b ? 1)^1/2 with j ≈ 0.4. The hard phase is augmented by filler and grows with increasing strain up to the prestretch.     

Viscoelastic properties of crosslinked solutions of poly(β-hydroxyethyl methacrylate) in diethylene glycol. II. Dependence of creep compliance on concentration in the rubbery zone

Creep compliance data, J(t), at 35°C for poly(β-hydroxyethyl monomethacrylate), crosslinked by ethylene glycol dimethacrylate in a range of concentration C from 0.0855 to 2.053 × 10^?4 mole/cm³ and swollen to various degrees in diluents, were examined for time-concentration superposition. From the dependence of time scale shift factors on v₂, the volume fraction of polymer, free volume parameters were calculated for two samples with C = 0.0855 × 10^?4 and 0.136 × 10^?4 mole/cm³, swollen in the range of v₂ from 0.134 to 0.591. Special attention was given to the magnitude of the shift factor on the log J(t) axis and its dependence on concentration, which was found to depend substantially on the crosslinking and the swelling degrees of the samples. This shift was approximately log v₂ for lightly crosslinked samples, swollen to a small degree, measured in the neighborhood of the main transition. For higher degrees of crosslinking and/or swelling, the shift was much less and for the most highly crosslinked networks swollen to equilibrium it was even negative. The correction appears to be very sensitive to the strain of the effective chains and to the location on the time scale with respect to the transition and rubberlike zones of viscoelasic behavior. It was found that the parameters of the WLF equation calculated in our previous study from the time-temperature superposition of the creep curves in the rubber-glass transition are valid also for the rubberlike region.     

Effect of Chloride Ions on the Hydrolysis of Trivalent Lanthanum,Praseodymium and Lutetium in Aqueous Solutions of 2 <Emphasis Type="Italic">M</Emphasis> Ionic Strength

The solubility product of the solid hydroxides and the first hydrolysis constants of trivalent ions of lanthanum, praseodymium and lutetium, were determined in 2 M NaClO₄(aq) and 2 M NaCl(aq) at 303 K, where M denotes the concentration in mol-L⁻¹. Solubility diagrams (pLn_(aq)−pC_H) were measured by means of a radiochemical method. The pC_H borderlines of precipitation and the solubility products were determined from these diagrams. The fitting of the solubility equation with the experimental values from the pLn_(aq)−pC_H diagrams also allowed the calculation of the first hydrolysis constants and the solubility products. In separate experiments, the stability constants for the first monohydroxide species were determined by means of potentiometric pH titrations, where the data were treated with both the program SUPERQUAD and by fitting of the results to the mean ligand number equation. Values of the log₁₀ < eqid20 > _1,Cl constants for the LnCl²⁺ species were also calculated at 2 M ionic strength and 303 K, using the hydrolysis constants obtained in both perchlorate and chloride media. The quantitative effects of chloride ions on the hydrolysis reactions and solubilities were determined for these three rare-earths spanning the lanthanide series.     

Vinyl polymerization. 179. Effects of substituents on chain transfer reaction of substituted cumenes toward poly(methyl methacrylate) radical

In order to study the effects of substituents on the chain transfer reaction to cumenes, the polymerization of methyl methacrylate in a series of nuclear-substituted cumenes with α,α′-azobisisobutyronitrile as initiator was carried out at 60°C. and the chain transfer constants C were determined. The C values obtained for all substituted cumenes were greater than that (C₀) for unsubstituted cumene, regardless of the electronattracting or -repelling nature of the substituents. Hence the plot of log (C/C₀) against the Hammett σ constants gave no linear relationship. When the plots were made by the modified Hammett equation including resonance effect of the substituents: log (C/C) = ρσ + γE_R, however, a straight line with ρ = 0.03 and γ = 0.9 was obtained. From these results, it may be concluded that the effect of the substitutents on the chain transfer reactivities of cumenes toward attack of a poly(methyl methacrylate) radical is attributable mainly to the resonance contribution in the transition state. These results are also compared with those for polystyryl radical reported previously and discussed.     

Pyrolysis of Propyne/2-Methylbut-1-ene-3-yne mixtures between 350 and 450°C

2-Methylbut-1-ene-3-yne and Propyne mixtures were pyrolyzed at 350–450°C in the absence and presence of O₂ and NO. The major product of the reaction is a polymer, but m-xylene and p-xylene are also produced and were studied as the species of interest. The C₈H₁₀ formation rate is first-order in C₃H₄ and C₅H₆. The rate coefficient is best fitted by though it is not inconsistent with where R is the ideal gas constant in kJ/mol-K. Experiments in the presence of NO show that m-xylene and p-xylene formation occur by two processes: a concerted molecular mechanism (? 41%) and a singlet diradical mechanism (? 59%).     

Effect of water on the mechanical properties of collagen films

The effect on water on mechanical properties of collagen films has been studied. The S-shaped sorption isotherm is separated into an adsorption curve C₁ and a solution curve C₂. From the C₂ curve, a value of 0.8 is calculated for the Flory-Huggins interaction parameter χ₁. The dynamic shear modulus G′, loss modulus G″, and loss tangent tan δ determined as functions of water content indicate two dispersions at low and at high water content. The region of water content from about 0.05 to 0.1 g/g, G′ decreases suddenly, G″ has a peak, and tan δ increases, corresponds to the region where the C₂ component of sorption becomes detectable. Another dispersion occurs at water contents above 0.2 g/g. A composite curve can be obtained by shifting stress-relaxation curves obtained at different humidities along the log time axis. When only the C₂ component of sorbed water is taken into account, the shift factor a_c is explained by a relation of Fujita and Kishimotos' based on free-volume theory. Shift factor for the relaxation curves of wool fibers, except for an initial part at times of less than 1 sec, are described by the same equation. The parameter β in the equation has the same value of 0.16 for both collagen and wool.     

Temperature dependence of the rate constants of cryochemical reactions

The temperature dependence of the reaction rate constant for tunneling transfer of an atomic particle in solid near absolute zero was studied. Different mechanisms describing the temperature dependence were considered: reorganization of the medium, modulation of parameters of the potential barrier, and under-barrier friction. It was established that for the rate constant (K) at low temperatures the equation InK=InK ₀+C ₄ T ⁴+C ₅ T ⁵+C ₆ T ⁶+C ₈ T ⁸ is valid. Experimental data were compared with the theory. A good agreement is achieved when the quantum nature of the hydrogen crystal is applied under the assumption of a predominant role of reorganization of the medium. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1906–1914, October, 1999.     

Electronic structures and nonlinear optical properties of highly deformed halofullerenes C3v C60F18 and D3d C60Cl30

Electronic structures and nonlinear optical properties of two highly deformed halofullerenes C_3v C₆₀F₁₈ and D_3d C₆₀Cl₃₀ have been systematically studied by means of density functional theory. The large energy gaps (3.62 and 2.61 eV) between the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs) and the strong aromatic character (with nucleus‐independent chemical shifts varying from ?15.08 to ?23.71 ppm) of C₆₀F₁₈ and C₆₀Cl₃₀ indicate their high stabilities. Further investigations of electronic property show that C₆₀F₁₈ and C₆₀Cl₃₀ could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states and frontier molecular orbitals are also calculated, which present that HOMOs and LUMOs are mainly distributed in the tortoise shell subunit of C₆₀F₁₈ and the aromatic [18] trannulene ring of C₆₀Cl₃₀, and the influence from halogen atoms is secondary. In addition, the static linear polarizability and second‐order hyperpolarizability of C₆₀F₁₈ and C₆₀Cl₃₀ are calculated using finite‐field approach. The values of and for C₆₀F₁₈ and C₆₀Cl₃₀ molecules are significantly larger than those of C₆₀ because of their lower symmetric structures and high delocalization of π electrons. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010