Thermal analysis of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine

The melting temperature, melting enthalpy, and specific heat capacities (C _p) of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine (DIOIPF) were measured using DSC-60 Differential Scanning Calorimetry. The melting temperature and melting enthalpy were obtained to be 453.80 K and 33.22 J g^?1, respectively. The relationship between the specific heat capacity and temperature was obtained to be C _p/J g^?1 K^?1 = 2.0261 – 0.0096T + 2 × 10^?5 T ² at the temperature range from 320.15 to 430.15 K. The thermal decomposition process was studied by the TG–DTA analyzer. The results showed that the thermal decomposition temperature of DIOIPF was above 487.84 K, and the decomposition process can be divided into three stages: the first stage is the decomposition of impurities, the mass loss in the second stage may be the sublimation of iodine and thermal decomposition process of the side-group C₄H₂O₂N₂F, and the third stage may be the thermal decomposition process of both the groups –CH₃ and –CH₂OCH₂–. The obtained thermodynamic basic data are helpful for exploiting new synthetic method, engineering design, and commercial process of DIOIPF.     

Heat of immersion of iron(III) oxides in water at 25°C

The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe₂O₃ (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, T_p, from 300 to 700°C. The samples were evacuated at outgassing temperature, T_o, between room temperature and 500°C at a pressure of 1 × 10^?2?2.7 × 10^?2N m^?2 for 6 h. The heat of immersion, h_i(J m^?2), of samples C and M increased with an increase in T_o and showed the maximum h_i at T_o =400°C, while sample F did not show the maximum up to T_o =500°C. The systematic correlation was not observed between h_i and T_p of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 10⁴ J mole^?1 H₂O.     

Absolute rate constant for the reaction of OH with thiophene between 293 and 473 K

The rate parameters of the OH + C₄H₄S (thiophene) reaction were measured at a pressure of 0.5 Torr in the temperature range 293–473 K by the discharge flow EPR method. The reaction was found to exhibit a negative temperature dependence. The data fit the Arrhenius expression k = (1.3 ± 0.8) × 10^?13 exp[(1750 ± 200)/T] cm³ molecule^?1 s^?1. The rate constant of (5 ± 0.4) × 10^?11 at room temperature corresponds to a short lifetime of C₄H₄S in the atmosphere.     

The rate of the reactions of C2O radicals with H and H2

The rate constants for the reactions C₂O + H → products (1) and C₂O + H₂ → products (2) have been determined at room temperature by means of laser-induced fluorescence detection of C₂O radicals, generated either by the KrF excimer laser photolysis Of C₃O₂, or by the reaction of C₃O₂ with O atoms. Values of k₁ = (3.7 ± 1.0) × 10^?11 cm³ s^?1 and k₂ = (7 ± 3) × 10^?13 cm³ s^?1 were obtained.     

Kinetics of phenyl radical reactions with propane,n‐butane,n‐hexane,and n‐octane: Reactivity of C6H5 toward the secondary C?H bond of alkanes

The kinetics of C₆H₅ reactions with n‐C_nH_2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C₆H₅COCH₃ as the phenyl precursor at temperatures between 494 and 1051 K. The rate constants were determined by kinetic modeling of the absolute yields of C₆H₆ at each temperature. Another major product C₆H₅CH₃ formed by the recombination of C₆H₅ and CH₃ could also be quantitatively modeled using the known rate constant for the reaction. A weighted least‐squares analysis of the four sets of data gave k (C₃H₈) = (1.96 ± 0.15) × 10¹¹ exp[?(1938 ± 56)/T], and k (n‐C₄H₁₀) = (2.65 ± 0.23) × 10¹¹ exp[?(1950 ± 55)/T] k (n‐C₆H₁₄) = (4.56 ± 0.21) × 10¹¹ exp[?(1735 ± 55)/T], and k (n?C₈H₁₈) = (4.31 ± 0.39) × 10¹¹ exp[?(1415 ± 65)T] cm³ mol^?1 s^?1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C₆H₅ with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least‐squares analyses of these two sets of data gave rise to k (n?C₄H₁₀) = (2.70 ± 0.15) × 10¹¹ exp[?(1880 ± 127)/T] and k (n?C₆H₁₄) = (4.81 ± 0.30) × 10¹¹ exp[?(1780 ± 133)/T] cm³ mol^?1 s^?1 for the temperature range 297‐‐1046 K. From the absolute rate constants for the two larger molecular reactions (C₆H₅ + n‐C₆H₁₄ and n‐C₈H₁₈), we derived the rate constant for H‐abstraction from a secondary C? H bond, k_s?CH = (4.19 ± 0.24) × 10¹⁰ exp[?(1770 ± 48)/T] cm³ mol^?1 s^?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 49–56, 2004     

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes (HTCC–Cd) was investigated by thermogravimetric analysis. The results indicate that the degradation of HTCC–Cd in nitrogen atmosphere was two-step reaction. For the first step of degradation, the initial temperature of mass loss (T ₀), the final temperature of mass loss (T _f), and the temperature of maximum mass loss (T _p) increase linearly with the rising of heating rate (B). T _o = 1.241B + 220.3, T _p = 1.111B + 245.8, and T _f = 1.335B + 358.2. Using different methods, the kinetic parameters of the two steps were investigated. The results show that the activation energies of the first step of degradation obtained using Friedman and Flynn–Wall–Ozawa methods are 1.684 × 10⁵ and 1.646 × 10⁵ J mol^?1, and the corresponding activation energies for the second step are 1.165 × 10⁵ J mol^?1 and 1.373 × 10⁵ kJ mol^?1. The results obtained from Phadnis–Deshpande methods indicate that the two degradation processes are both nucleation and growth process, and follow A₄ mechanism with intergral form g(X) = [?ln(1 ? X)]⁴.     

Kinetics and mechanism of atmospheric reactions of partially fluorinated alcohols

Gas-phase reactions typical of the Earth’s atmosphere have been studied for a number of partially fluorinated alcohols (PFAs). The rate constants of the reactions of CF₃CH₂OH, CH₂FCH₂OH, and CHF₂CH₂OH with fluorine atoms have been determined by the relative measurement method. The rate constant for CF₃CH₂OH has been measured in the temperature range 258–358 K (k = (3.4 ± 2.0) × 10¹³exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(1.5 ± 1.3) kJ/mol). The rate constants for CH₂FCH₂OH and CHF₂CH₂OH have been determined at room temperature to be (8.3 ± 2.9) × 10¹³ (T = 295 K) and (6.4 ± 0.6) × 10¹³ (T = 296 K) cm³ mol^?1 s^?1, respectively. The rate constants of the reactions between dioxygen and primary radicals resulting from PFA + F reactions have been determined by the relative measurement method. The reaction between O₂ and the radicals of the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH) have been investigated in the temperature range 258–358 K to obtain k = (3.8 ± 2.0) × 10⁸exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(10.2 ± 1.5) kJ/mol. For the reaction between O₂ and the radicals of the general formula C₂H₄FO (? HFCH₂O, CH₂F?HOH, and CH₂FCH₂?) at T = 258–358 K, k = (1.3 ± 0.6) × 10¹¹exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(5.3 ± 1.4) kJ/mol. The rate constant of the reaction between O₂ and the radicals with the general formula C₂H₃F₂O (?F₂CH₂O, CHF₂?HOH, and CHF₂CH₂?) at T = 300 K is k = 1.32 × 10¹¹ cm³ mol^?1 s^?1. For the reaction between NO and the primary radicals with the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH), which result from the reaction CF₃CH₂OH + F, the rate constant at 298 K is k = 9.7 × 10⁹ cm³ mol^?1 s^?1. The experiments were carried out in a flow reactor, and the reaction mixture was analyzed mass-spectrometrically. A mechanism based on the results of our studies and on the literature data has been suggested for the atmospheric degradation of PFAs.     

The rate constants of the gas-phase reactions K + Cl ⇆ K+ + Cl− and KCl + M ⇆ K+ + Cl− + M from measurements in atmospheric pressure flames

Mass spectrometric studies of the ions present in H₂/O₂/N₂ flames with potassium and chlorine added have demonstrated that ionization can occur in the forward steps of K + Cl ? K⁺ + Cl^? (II), KCl + M ? K⁺ + Cl^? + M (IV), where M is any third body. Variations of [K⁺] with time in these systems have been measured and establish that the rate coefficients (in ml molecule^?1 s^?1) of the ion-producing steps are k₂ = 5 × 10^?10T^{?$\text{1}\text{2}$} exp(?10 500/T) and k₄ = 2.2 × 10⁷T^?3.5 × exp(?60 800/T). Coefficients for ion-ion recombination have been obtained from k₂ and k₄ using the equilibrium constants of (II) and (IV) and are k_?2 = 1.7 × 10^?9T^{?$\text{1}\text{2}$} and k_?4 = 1.1 × 10^?17T^?3, with each one in the ml molecule^?1 s^?1 system of units. Replacement of the N₂ in one of these flames with sufficient Ar to maintain the temperature constant leaves the measured k₂ and k_?2 unchanged, but lowers the observed k₄ and k_?4. This confirms that ion-recombination in the backward step in (II) is a two-body process, whereas in (IV) it is termolecular.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.     

Kinetics and mechanisms for reactions of HNO with CH3 and C6H5 studied by quantum‐chemical and statistical‐theory calculations

Kinetics and mechanisms for the reactions of HNO with CH₃ and C₆H₅ have been investigated by ab initio molecular orbital (MO) and transition‐state theory (TST) and/or Rice‐Ramsperger‐Kassel‐Marcus/Master Equation (RRKM/ME) calculations. The G2M(RCC, MP2)//B3LYP/6‐31G(d) method was employed to evaluate the energetics for construction of their potential energy surfaces and prediction of reaction rate constants. The reactions R + HNO (R = CH₃ and C₆H₅) were found to proceed by two key product channels giving (1) RH + NO and (2) RNO + H, primarily by direct abstraction and indirect association/decomposition mechanisms, respectively. As both reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our TST and RRKM/ME calculations. For practical applications, the rate constants evaluated for the atmospheric‐pressure condition are represented by modified Arrhenius equations in units of cm³ mol^?1 s^?1 for the temperature range 298–2500 K: κ_1A = 1.47 × 10¹¹ T ^0.76 exp[?175/ T ], κ_2A = 8.06 × 10³ T ^2.40 exp[?3100/ T ], κ_1B = 3.78 × 10⁵ T ^2.28 exp[230/ T ], and κ_2B = 3.79 × 10⁹ T ^1.19 exp[?4800/ T ], where A and B represent CH₃ and C₆H₅ reactions, respectively. Based on the predicted rate constant at 1 atm pressure for R + HNO → RNO + H, we estimated their reverse rate constants for R + HNO production from H + RNO in units of cm³ mol^?1 s^?1: κ_?2A′ = 7.01 × 10¹⁰ T ^0.84 exp[120/ T ] and κ_?2B′ = 2.22 × 10¹⁹ T ^?1.01 exp[?9700/ T ]. The heats of formation at 0 K for CH₃NO, CH₃N(H)O, CH₃NOH, C₆H₅N(H)O, and C₆H₅NOH have been estimated to be 18.6, 18.1, 22.5, 47.2, and 50.7 kcal mol^?1 with an estimated ±1 kcal mol^?1 error. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 261–274, 2005     

The 1B1u ← 1A1g 0—0 transition in crystal benzene

The transition linewidth ΔE in crystal C₆H₆, C₆D₆ and sym-C₆H₃D₃ has been measured as a function of temperature T from 4.2 to 135°K, and it extrapolates to a common value of ΔE_o = 50 cm^? at O°K. In C₆H₆ ΔE = (50 + 7T^{$\text{1}\text{2}$}) cm^?1, indicative of strong exciton—phonon coupling, and there is a line shift of +40 cm^?1 per substituent deuteron. Fluorescence excitation spectral data are used to separate the ¹B_1u(= S₂) decay rate k_H = 9.4 × 10¹² sec^?1, derived from ΔE₀, into S₂S₁ internal conversion (rate ≈ 6.6 × 10¹² sec^?1) and S₂S_x (channel 3) internal conversion (rate ≈ 2.8 × 10¹² sec^?1. A similar value of k_H = 9.9 × 10¹² sec^?1 is obtained from the S₂S_o fluorescence quantum yield of liquid benzene.     

The structure and dynamics of the copper(II)—l-proline 1:2 complex in solution

The ¹³C relaxation times (T₁ and T₂) and isotropic contact shifts (Δω) of a one molar aqueous solution of l-proline at pH = 11 (or pD = 11.4) containing ca 10^?4 M copper(II) perchlorate are measured at 62.86 MHz over a temperature range of 26–70°C. The purely dipolar longitudinal relaxation of carbon-13 nuclei contrasting with purely scalar transverse relaxation allowed us to extract carbon-to-metal distances (through T₁ measurements) and hyperfine coupling constants and dynamic parameters (from T₂ and Δω measurements). The structure of the complex in solution is found closely similar to that in the solid state. Curve-fitting procedures allowed us to derive the hyperfine electron—carbon coupling constants A_c = ?1.95, + 0.42, + 1.90 and ?1.70 MHz for carbons α, β, γ, δ, of the pyrrolidinic ring, the reorientation correlation time of the complex, τ_R (25°C) = 1.15 × 10^?10 sec, the l-proline exchange rate, k_M (25°C) = 4.0 × 10⁵ sec^?1 (and the corresponding activation parameters ΔH^≠ = 9.0 kcal mol^?1 and ΔS^≠ = ?0.7 e.u.), and the electronic relaxation time, T_1e = 1.13 × 10^?8 sec (at 25°C). The latter value was found in agreement with the one computed from ESR data and the above τ_R value, showing the predominant contributions of spin—rotation interaction and, to a lesser extent, of the effect of g-tensor anisotropy to the electronic relaxation rate.     

Rate constant of the gas-phase reaction between Fe atoms and CO2

The rate constant of the gas-phase reaction Fe(a ⁵ D ₄) + CO₂ at 1180–2380 K and a total gas density of (7.0–10.0) × 10^?6 mol/cm³ behind incident shock waves is k(Fe + CO₂) = 1.4 × 10^{14.0 ± 0.3}exp[?(14590 ± 1100)/T] cm³ mol^?1 s^?1, as determined by resonance atomic absorption photometry. Using thermochemical data available from the literature, the rate constant of the reverse reaction was calculated to be k(Fe + CO) = 9.2 × 10^{11.0 ± 0.3} (T/1000)^0.57exp[?(490 ± 1100)/T] cm³ mol^?1 s^?1. The results are compared with data reported earlier.     

Kinetics of the reactions of C2H5, n‐C3H7, and n‐C4H9 radicals with Cl2 at the temperature range 190–360 K

The kinetics of the C₂H₅ + Cl₂, n‐C₃H₇ + Cl₂, and n‐C₄H₉ + Cl₂ reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time‐resolved measurements to obtain reaction rate coefficients under pseudo‐first‐order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5–5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C₂H₅ + Cl₂) = (1.45 ± 0.04) × 10^?11 (T/300 K)^{?1.73 ± 0.09} cm³ molecule^?1 s^?1 (190–359 K), k(n‐C₃H₇ + Cl₂) = (1.88 ± 0.06) × 10^?11 (T/300 K)^{?1.57 ± 0.14} cm³ molecule^?1 s^?1 (204–363 K), and k(n‐C₄H₉ + Cl₂) = (2.21 ± 0.07) × 10^?11 (T/300 K)^{?2.38 ± 0.14} cm³ molecule^?1 s^?1 (202–359 K), with the uncertainties given as one‐standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C₂H₅ + Cl₂ reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614–619, 2007     

Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane

Excess molar volumes V_m^E at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C₄H₉Cl + (1 ? x)n-C_lH_{2l + 2}}, and II: {x1,4-C₄H₈Cl₂ + (1 ? x)n-C_lH_{2l + 2}}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C_{p, m}^E at constant pressure. V_m^E is positive for all mixtures in series I: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, V_m^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆} is small and S-shaped, the maximum being situated at x_max = 0.178 with V_m^E(x_max)/(cm³ · mvl^?1) = 0.095, and the minimum is at x_min = 0.772 with V_m^E(x_min)/(cm³ · mol^?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.458 for l = 10, and 0.771 for l = 14. The C_{p, m}^Es of series I are all negative and |C_{p, m}^E| increases with increasing l: at x = 0.5, C_{p, m}^E/(J · K^?1 · mol^?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for C_{p, m}^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆}. The more prominent minimum is situated at x′_min = 0.184 with C_{p, m}^E(x′_min)/(J · K^?1 · mol^?1) = ?0.62, and the less prominent at x″_min = 0.703 with C_{p, m}^E(x″_min)/(J · K^?1 · mol^?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (x_min = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.     

The temperature dependence of the OH radical reactions with some aromatic compounds under simulated tropospheric conditions

The temperature dependence of the rate coefficients for the OH radical reactions with toluene, benzene, o-cresol, m-cresol, p-cresol, phenol, and benzaldehyde were measured by the competitive technique under simulated atmospheric conditions over the temperature range 258–373 K. The relative rate coefficients obtained were placed on an absolute basis using evaluated rate coefficients for the corresponding reference compounds. Based on the rate coefficient k(OH + 2,3-dimethylbutane) = 6.2 × 10^?12 cm³ molecule^?1s^?1, independent of temperature, the rate coefficient for toluene k_OH = 0.79 × 10^?12 exp[(614 ± 114)/T] cm³ molecule^?1 s^?1 over the temperature range 284–363 K was determined. The following rate coefficients in units of cm³ molecule^?1 s^?1 were determined relative to the rate coefficient k(OH + 1,3-butadiene) = 1.48 × 10^?11 exp(448/T) cm³ molecule^?1 s^?1: o-cresol; k_OH = 9.8 × 10^?13 exp[(1166 ± 248)/T]; 301–373 K; p-cresol; k_OH = 2.21 × 10^?12 exp[(943 ± 449)/T]; 301–373 K; and phenol, k_OH = 3.7 × 10^?13 exp[(1267 ± 233)/T]; 301–373 K. The rate coefficient for benzaldehyde k_OH = 5.32 × 10^?12 exp[(243 ± 85)/T], 294–343 K was determined relative to the rate coefficient k(OH + diethyl ether) = 7.3 × 10^?12 exp(158/T) cm³ molecule^?1 s^?1. The data have been compared to the available literature data and where possible evaluated rate coefficients have been deduced or updated. Using the evaluated rate coefficient k(OH + toluene) = 1.59 × 10^?12 exp[(396 ± 105)/T] cm³ molecule^?1 s^?1, 213–363 K, the following rate coefficient for benzene has been determined k_OH = 2.58 × 10^?12 exp[(?231 ± 84)/T] cm³ molecule^?1 s^?1 over the temperature range 274–363 K and the rate coefficent for m-cresol, k_OH = 5.17 × 10^?12 exp[(686 ± 231)/T] cm³ molecule^?1 s^?1, 299–373 K was determined relative to the evaluated rate coefficient k(OH + o-cresol) = 2.1 × 10^?12 exp[(881 ± 356)/T] cm³ molecule^?1 s^?1. The tropospheric lifetimes of the aromatic compounds studied were calculated relative to that for 1,1,1-triclorethane = 6.3 years at 277 K. The lifetimes range from 6 h for m-cresol to 15.5 days for benzene. © 1995 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     

Kinetics of CH(X2Π) radical reactions with propane,isobutane and neopentane

Rate constants over the temperature range 298–689 K are reported for the reaction of CH(X²Π) radicals with C₃H₈, i-C₄H₁₀ and neo-C₅H₁₂. The CH radical was generated by multiphoton laser photolysis of CHBr₃ and its disappearance monitored by laser-induced fluorescence (LIF) at 429.8 nm. Absolute rate constants were determined as a function of temperature and total pressure. The following Arrhenius parameters were derived: k = (1.85 ± 0.13) × 10⁻¹⁰ exp[(240±30)/T] cm³/s for CH+propane; k = (2.03±0.19)×10⁻¹⁰ exp[(240±40)/T] cm³/s for CH+isobutane; k = (1.61±0.10)×10⁻¹⁰ exp[(340±30)/T] cm³/s for CH+neopentane, all independent of total pressure. The negative temperature dependences along with the energetics and lack of pressure effects lead to the conclusion that the reactions proceed by CH insertion into the alkane. The activated adduct thus formed rapidly decomposes via many energetically accessible channels. An analysis of CH reactions with C₁ to C₅ alkanes shows an increase in the room temperature rate constants in going from C₁ to C₄ irrespective of the nature of CH bonds. The rate constant then begins to level off near ≈ 5 × 10⁻¹⁰ cm/s for C₄ and C₅ alkanes.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). III. Kinetic study of the branching reaction in the radical polymerization of vinyl acetate

The branching reaction in the radical polymerization of vinyl acetate was studied kinetically. Branching occurs by polymer transfer as well as terminal double-bond copolymerization. The chain-transfer constants to the main chain (C_p,2) and to the acetoxy methyl group (C_p,1) on the polymer were calculated on the basis of the experimental data described in the preceding paper giving C_p,2 = 3.03 × 10^?4, C_p,1 = 1.27 × 10^?4 at 60°C, and C_p,2 = 2.48 × 10^?4, C_p,1 = 0.52 × 10^?4 at 0°C. Chain transfer to monomer is important with respect to the formation of the terminal double bond. The total values of transfer constants to the α- or β-position in the vinyl group and the acetoxymethyl group in vinyl acetate was determined to be 2.15 × 10^?4 at 60°C. The transfer constant to the acetyl group in the monomer (C_m,1) was also evaluated to be 2.26 × 10^?4 at 60°C from the quantitative determination of the carboxyl terminals in PVA. These facts suggest that the chain-transfer constant to the α- or β-position in the monomer (C_m,2) is nearly equal to zero within experimental error. Copolymerization reactivity parameters of the terminal double bond were also estimated. In conclusion, it has become clear that the formation of nonhydrolyzable branching by the terminal double-bond reaction can be almost neglected, and hence that the long branching in PVA is formed only by the polymer transfer mechanism. On the other hand, a large number of hydrolyzable branches in PVAc are prepared by the terminal double-bond reaction rather than by polymer transfer.     

Selected rate constants for H,O, N,and Cl atoms with substrates at room temperatures

Rate constants for H + Cl₂, H + CH₃CHO, H + C₃H₄, O + C₃H₆, O + CH₃CHO, and Cl + CH₄ have been measured at room temperature by the discharge flow—resonance fluorescence technique. The results are (1.6 ± 0.1) × 10^?11, (9.8 ± 0.8) × 10 ^?14, (6.3 ± 0.4) × 10^{?13) (2.00 torr He), (3.95 ± 0.41) × 10?12, (4.9 ± 0.5) × 10|su?13} and (1.08 ± 0.07) × 10^?13, respectively, all in units of cm³ molecule^?1 s^?1. Also N atom reactions with C₂H₂, C₂H₄, C₃H₄, and C₃H₆ were studied but in no case was there an appreciable rate constant. These results are compared to previous studies.