Über Osmiumbromide

On Osmiumbromides OsBr₄ was obtained by reaction of OsCl₄ with bromine in a closed system at 330°C and 120 bar Br₂ pressure. The compound crystallizes orthorhombic (a = 633.99(18) pm; b = 1 210.92(16) pm; c = 1 461.5(10) pm; Z = 8; space group Pbca) in a TcCl₄ type structure. OsBr₆ octahedra are connected by two common edges to \documentclass{article}\pagestyle{empty}\begin{document}${}_\infty ^1 \left[ {{\rm OsBr}_{{{\rm 2} \mathord{\left/ {\vphantom {{\rm 2} 1}} \right. \kern-\nulldelimiterspace} 1}} {\rm Br}_{{{\rm 4} \mathord{\left/ {\vphantom {{\rm 4} 2}} \right. \kern-\nulldelimiterspace} 2}} } \right]$\end{document} chains with a cis arrangement of the two non-bridging Br atoms. Mixed crystals OsBr_xCl_4?x(0 < x < 2.3) with CsCl₄ type structure are formed by reactions at lower Br₂ pressure up to 12 bar. They are built up from chains consisting of edge-sharing octahedra. The terminal atoms have a trans arrangement. Attempts to synthesize single crystals of OsBr₃ by decomposition of OsBr₄ resulted in formation of three different phases OsBr_x (3 < x < 4).     

Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3-amino-4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO₂/CH₄ separation ( $ {\rm P}_{{\rm CO}_2 } $ = 6.1 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, and $ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $ = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6-naphthalene dicarbonyl chloride displays high performance for H₂/CO or H₂/CH₄ separation ( $ {\rm P}_{{\rm H}_2 } $ = 2.4 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $ = 71, and $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $ = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.     

Stable [C2H7O2]+ isomers: Experimental and theoretical evidence for the existence of protonated peroxides and proton-bound dimers in the gas phase

Evidence is presented for the gas phase generation of at least eight stable isomeric [C₂H₇O₂]⁺ ions. These include energy-rich protonated peroxides (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_2 {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (e), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm (H)OH} $\end{document} (f) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm (H)CH}_{\rm 3} {\rm (g)),} $\end{document} (g)), proton-bound dimers (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm 3} \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} (h) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH2 = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm + } \cdot \cdot \cdot {\rm HOCH}_{\rm 3} $\end{document} (i)) and hydroxy-protonated species (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} {\rm (OH)CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} (a), $\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH(OH)}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (b) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm OCH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (c)). The important points of the present study are (i) that these ions are prevented by high barriers from facile interconversion and (ii) that both electron-impact- and proton-induced gas phase decompositions seem to proceed via multistep reactions, some of which eventually result in the formation of proton-bound dimers.     

Pyrolysis of dimethyl peroxide

By using isobutane (t-BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110–140°C in a static system. For low concentrations of DMP (2.5 × 10^?5?10^?4M) and high pressures of t?BuH (～0.9 atm) the first-order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): \documentclass{article}\pagestyle{empty}\begin{document}${\rm DMP}\mathop \to \limits^1 2{\rm Me}\mathop {\rm O}\limits^{\rm .},{\rm Me}\mathop {\rm O}\limits^{\rm .} + t{\rm - BuH}\mathop \to \limits^4 {\rm MeOH} + t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u}$\end{document}. For complete decomposition of DMP in t-BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}. In the decomposition of pure DMP complications arise due to the H-abstraction reactions of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document} from DMP and the product CH₂O. The rate constant for reaction (1) is given by k₁ = 10^15.5?37.0/θ sec^?1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeO? OMe) = 37.6 ± 0.2 kcal/mole and /H(Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(RO? OR) and D(RO? H) are unaffected by the nature of R. From ΔS and A₁, k₂ is calculated to be 10^10.3±0.5 M^?1· sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2{\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^2 {\rm DMP}$\end{document}. For complete reaction, trace amounts of t-BuOMe lead to the result k₂ ～ 10⁹ M^?1 ·sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - Bu}\mathop \to \limits^5$\end{document} products. From the relationship k₆ = 2(k₂k_5a)^1/2 and with k_5a = 10^8.4 M^?1 · sec^?1, we arrive at the result k₆ = 10^9.7 M^?1 · sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - u}\mathop {\rm B}\limits^{\rm .} \to (t{\rm - Bu)}_{\rm 2}{\rm,}t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u} + {\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^6 t{\rm - BuOMe}$\end{document}.     

Magnetische Struktur von Columbit,FeNb2O6

The atom parameters of columbite. FeNb₂O₆ and MnNb₂O₆, are refined by neutron diffraction. Low temperature measurements of FeNb₃O₆ provided magnetic reflections hkl with k half integer. From the intensities of the reflections a collinear magnetic structure \documentclass{article}\pagestyle{empty}\begin{document}$ \overrightarrow {\rm S} _1 = - \overrightarrow {\rm S} _2 = \overrightarrow {\rm S} _3 = \overrightarrow {\rm S} _4 $\end{document} results for the 4 atoms of the half of the magnetic unit cell. The moments lie parallel to the x-axis, φ_a = 0°. The moment is μ = 3.84 μ_B. For MaNb₂O₆ at 2.0°K reflections 010, 101 and 210 are observed additionally. From the observed intensities it is possible to distinguish a collinear model G: \documentclass{article}\pagestyle{empty}\begin{document}$ \overrightarrow {\rm S} _1 = - \overrightarrow {\rm S} _2 = \overrightarrow {\rm S} _3 = - \overrightarrow {\rm S} _4 $\end{document} with components G_x, G_z (φ_a = 10°, φ_c = 80°), and a non-collinear model C_x (\documentclass{article}\pagestyle{empty}\begin{document}$ \overrightarrow {\rm S} _1 = \overrightarrow {\rm S} _2 = - \overrightarrow {\rm S} _3 = - \overrightarrow {\rm S} _4 $\end{document}) with G_y in favour of the first one.     

Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C

The constants for the dissociation of citric acid (H₃C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm^–3) at 25 °C. The stoichiometric dissociation constants (K_i^*)

Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study

Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnO_x) with various solid‐state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnO_x was then investigated with Ce⁴⁺ as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 or about 50 μmol_O2 m^?2 h^?1. In comparison, catalytic rates per mole of Mn of oxides characterised by well‐defined 3D networks were rather low (e.g., ca. 90 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 for bixbyite, Mn₂O₃), but impressive if normalised per unit surface area (>100 ${{\rm{{\rm \mu} mol}}_{{\rm{O}}_{\rm{2}} } }$ m^?2 h^?1 for marokite, CaMn₂O₄). Thus, two groups of MnO_x emerge from this screening as hot candidates for manganese‐based WOC materials: 1) amorphous oxides with tunnelled structures and the well‐established layered oxides; 2) crystalline Mn^III oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass.     

The gas-phase pyrolysis of alkyl nitrites. III. Isopropyl nitrite

The rate of decomposition of isopropyl nitrite (IPN) has been studied in a static system over the temperature range of 130–160°C. For low concentrations of IPN (1–5 × 10^?5M), but with a high total pressure of CF₄ (～0.9 atm) and small extents of reaction (～1%), the first-order rates of acetaldehyde (AcH) formation are a direct measure of reaction (1), since k₃ » k₂(NO): \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$ {\rm IPN}\begin{array}{rcl} 1 \\ {\rightleftarrows} \\ 2 \\ \end{array}i - \Pr \mathop {\rm O}\limits^. + {\rm NO},i - \Pr \mathop {\rm O}\limits^. \stackrel{3}{\longrightarrow} {\rm AcH} + {\rm Me}. $\end{document} Addition of large amounts of NO (～0.9 atm) in place of CF₄ almost completely suppressed AcH formation. Addition of large amounts of isobutane – t-BuH – (～0.9 atm) in place of CF₄ at 160°C resulted in decreasing the AcH by 25%. Thus 25% of \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^{\rm .} $\end{document} were trapped by the t-BuH (4): \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + t - {\rm BuH} \stackrel{4}{\longrightarrow} i - \Pr {\rm OH} + (t - {\rm Bu}). $\end{document} The result of adding either NO or t-BuH shows that reaction (1) is the only route for the production of AcH. The rate constant for reaction (1) is given by k₁ = 10^{16.2±0.4–41.0±0.8}/θ sec^?1. Since (E₁ + RT) and ΔH°₁ are identical, within experimental error, both may be equated with D(i-PrO-NO) = 41.6 ± 0.8 kcal/mol and E₂ = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result that \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta H_f^\circ (i - {\rm Pr}\mathop {\rm O}\limits^{\rm .} ) = - 11.9 \pm 0.8{\rm kcal}/{\rm mol}. $\end{document} From ΔS°₁ and A₁, k₂ is calculated to be 10^10.5±0.4M^?1·sec^?1. From an independent observation that k₆/k₂ = 0.19 ± 0.03 independent of temperature we find E₆ = 0 ± 1 kcal/mol and k₆ = 10^9.8+0.4M^?;1·sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + {\rm NO} \stackrel{6}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} In addition to AcH, acetone (M₂K) and isopropyl alcohol (IPA) are produced in approximately equal amounts. The rate of M₂K formation is markedly affected by the ratio S/V of different reaction vessels. It is concluded that the M₂K arises as the result of a heterogeneous elimination of HNO from IPN. In a spherical reaction vessel the first-order rate of M₂K formation is given by k₅ = 10^9.4–27.0/θ sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm IPN} \stackrel{5}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} IPA is thought to arise via the hydrolysis of IPN, the water being formed from HNO. This elimination process explains previous erroneous results for IPN.     

Polymerization of σ-bonded organo-transition metal derivatives of styrene

Five new monomers of transition metal complexes containing a styryl group, trans-\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Pd}({\rm PBu}_{\rm 3})_2 \rlap{--} ({\rm C}_6 {\rm H}_4 {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm X\ X \hbox{=\hskip-2pt=} Cl(Ia),\ X \hbox{=\hskip-2pt=} Br(Ib)},\ {\rm X \hbox{=\hskip-2pt=} CN(Ic),\ X \hbox{=\hskip-2pt=} Ph(Id)} $\end{document} and trans-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Pt(PBu}_{\rm 3} {\rm )}_{\rm 2} \rlap{--} ({\rm C}_{\rm 6} {\rm H}_{\rm 4} {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm Cl}({\rm II})$\end{document}, were synthesized. The monomers were readily homopolymerized in benzene with the use of AIBN or BBu₃–oxygen as the initiator. Copolymerization of Ia with styrene was carried out by using AIBN. From the Cl content of the copolymers by analysis, monomer reactivity ratios and Q–e values were obtained as follows: r₁ = 1.49, r₂ = 0.45; Q₂ = 0.41, e₂ = ?1.4 (M₁ = styrene, M₂ = Ia). Based on the above data, the σ-bonded palladium moiety at para position of styrene acts as a strongly electron-donating group to the phenyl ring. This is also supported by the olefinic β-carbon chemical shift of ¹³C NMR for Ia.     

Effect of long-chain branching on the relation between steady-flow and dynamic viscosity of polyethylene melts

The steady-state viscosity η, the dynamic viscosity η′, and the storage modulus G′ of several high-density and low-density polyethylene melts were investigated by using the Instron rheometer and the Weissenberg rheogoniometer. The theoretical relation between the two viscosities as proposed earlier is:\documentclass{article}\pagestyle{empty}\begin{document}$ \eta \left( {\dot \gamma } \right){\rm } = {\rm }\int {H\left( {\ln {\rm }\tau } \right)} {\rm }h\left( \theta \right)g\left( \theta \right)^{{\raise0.7ex\hbox{$3$} \!\mathord{\left/ {\vphantom {3 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} \tau {\rm }d{\rm }\ln {\rm }\tau $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ \theta {\rm } = {\rm }{{\dot \gamma \tau } \mathord{\left/ {\vphantom {{\dot \gamma \tau } 2}} \right. \kern-\nulldelimiterspace} 2} $\end{document}; \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \gamma } $\end{document} is the shear rate, H is the relaxation spectrum, τ is the relaxation time, \documentclass{article}\pagestyle{empty}\begin{document}$ g\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{\theta \mathord{\left/ {\vphantom {\theta {\left( {1 + \theta ^2 } \right)}}} \right. \kern-\nulldelimiterspace} {\left( {1 + \theta ^2 } \right)}}} \right] $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ h\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} \mathord{\left/ {\vphantom {{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right. \kern-\nulldelimiterspace} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right] $\end{document}. Good agreement between the experimental and calculated values was obtained, without any coordinate shift, for high-density polyethylenes as well as for a low density sample with low n_w, the weight-average number of branch points per molecule. The correlation, however, was poor with low-density samples with large values of the long-chain branching index n_w. This lack of coordination can be related to n_w. The empirical relation of Cox and Merz failed in a similar way.     

Estimation of partial linear error-in-variables models for ρ<Superscript>−</Superscript>-mixing dependence data

Consider the partly linear regression model Y = xβ + g(t) + e where the explanatory x is erroneously measured, and both t and the response Y are measured exactly, the random error e is ρ⁻-mixing. Let be a surrogate variable observed instead of the true x in the primary survey data. Assume that in addition to the primary data set containing N observations of , which is ρ⁻-mixing data sets, an independent validation data containing n observations of is available. The exact observations on x may be obtained by some expensive or diffcult procedures for only a small subset of subjects enrolled in the study. In this paper, inspired by Berberan-Santos et al. [J. Math. Chem. 37 (2005)101], a semiparametric method with the primary data is employed to obtain the estimators of β and g(·) based on the least squares criterion with the help of validata. The proposed estimators are proved to be strongly consistent.      

Methyl thiirane: Kinetic gas-phase titration of sulfur atoms in SX OY systems

The reaction SO + SO →l S + SO₂(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C₃H₆ produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k₂ ? 3.5 × 10^?15 cm³/s at 298 K.     

Über Oxidsysteme mit Übergangsmetallionen in verschiedenen Oxydationsstufen. X. Elektronische und infrarotspektroskopische Untersuchungen am System Zn(ZnxV2−x)O4

The controlled valency semiconduction in the spinel system \documentclass{article}\pagestyle{empty}\begin{document}${\rm Zn}({\rm Zn}_{\rm x} \mathop {\rm V}\limits^{ + 3} _{2 - 2{\rm x}} \mathop {\rm V}\limits^{ + 4} _{\rm x}){\rm O}_4 (0 \le {\rm x} \le 0.50)$\end{document} is due to the controlled variation of the ratio V³⁺/V⁴⁺ at octahedral sites. The low temperature phase which is present according to X-ray patterns above x = 0.18 with an ordered cation distribution at the octahedral sites shows a higher specific electrical resistivity than the high temperature phase which is characterized by a random cation distribution. The activation energies, too, differ in the range x > 0.15. The whole region of solid solutions shows p-type conductivity. The thermo-EMF has a weak temperature dependence for x > 0.03. The IR spectra of both phases are identical in the range between 1000 and 200 cm^?1.     

Structure and formation of some [C4H5O2]+ ions generated by radical losses in pseudo simple cleavage reactions

Characterization of some [C₄H₅O₂]⁺ ions in the gas phase using their collisional activation mass spectra shows that the isomeric ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O,} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HC} \equiv {\rm C} - \mathop {{\rm C}({\rm OH}){\rm OCH}_3 }\limits^ + $\end{document} are stable for t?10^?5 s. Of these, ions of structure were generated by the site specific gas phase protonation of γ-crotonolactone with isobutane or methanol as chemical ionization reagent gases. These results and those derived from measurements on some ²H, ¹³C and ¹⁸O labelled [C₄H₅O₂]⁺ product ions, were used to study the mechanisms of unimolecular radical elimination reactions, viz. (1) loss of CH₃˙ from [trans-methyl crotonate], (2) loss of H˙ from [methyl acrylate]⁺˙, (3) loss of H˙ from [cyclopropane carboxylic acid]⁺˙ and (4) loss of CH₃˙ from [1,3-dimethoxypropyne]⁺˙. It is concluded that none of these losses occur by simple bond cleavage. Mechanisms are presented which account for the observation that the first three reactions yield product ions of structure whereas the ions generated by reaction (4) have structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}. It is further proposed that a minor fraction of the [M-CH₃]⁺ ions from ionized trans-methyl crotonate is generated via a rearrangement process which yields ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}.     

Kinetics of solvolysis of 1-acetyl-4-(1-ethoxycarbonyl-1-cyano) methylene-1,4-dihydroquinoline in undried DMSO-d6· formation of Acetic Anhydride as an intermediate

The kinetics of solvolysis of the title compound (QAc) in undried DMSO-d₆ to give 4-(1-ethoxycarbonyl-1-cyano)methylquinoline (QH) and HOAc at ambient temperature were investigated by ¹H nmr spectrometry. With a limited excess of water the solvolysis follows a three-step process of $ {\rm QAc} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_1} {\rm QH} + {\rm HOAc}, $ , and $ {\rm Ac}_{\rm 2} {\rm O} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_3} {\rm 2\,HOAc}, $ where k₂ > k₁ and k₃ < k₁. Addition of pyridine-d₅ to the reaction mixture markedly catalyzes the overall solvolysis, while addition of CF₃CO₂D to the reaction mixture simplifies the kinetics to pseudo first-order in [QAc] with k = 4.3 × 10^?3 min^?1.     

Kinetic study of the gas-phase reaction c-C5H8 + I2 ⇄ c-C5H6 + 2HI the heat of formation and the stabilization energy of the cyclopentenyl radical

The gas-phase dehydrogenation of cyclopentene to cyclopentadiene catalyzed by iodine in the range 178–283°C has been found to obey a rate law consistent with the slow rate-determining step, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm I} + {\rm c} - {\rm C}_5 {\rm H}_8 \stackrel{4}{\rightarrow}{\rm HI} + {\rm c} - {\rm C}_5 {\rm H}_7 $\end{document}, log [k₄/(1 mole^?1 sec^?1)] = 10.25 ± 0.08 - (12.26 ± 0.18)/θ, where θ = 2.303 R T in kcal/mole. Surface effects are not important. This value of E₄ leads to a value of DH = 82.3 ± 1 kcal/mole and ΔH_f298 = 38.4 ± 1 kcal/mole. From difference in bond strengths in the alkane and the alkene, the allylic resonance stabilization in the cyclopentenyl radical is 12.6 ± 1.0 kcal/mole, in excellent agreement with the value for the butenyl radical. Arrhenius parameters for the other steps in the mechanism are evaluated. The low value of A₄ (compared with A₄ for cyclopentane) suggests a “tighter” transition state for H-atom abstraction from alkenes than from alkanes.     

The gas-phase pyrolysis of alkyl nitrites. II. s-butyl nitrite

The rate of decomposition of s-butyl nitrite (SBN) has been studied in the absence (130–160°C) and presence (160–200°C) of NO. Under the former conditions, for low concentrations of SBN (6 × 10^?5 ? 10^?4M) and small extents of reaction (～1.5%), the first-order homogeneous rates of acetaldehyde (AcH) formation are a direct measure of reaction (1) since k_3c » k₂(NO): . Unlike t-butyl nitrite (TBN), d(AcH)/dt is independent of added CF₄ (～0.9 atm). Thus k_3c is always » k₂ (NO) over this pressure range. Large amounts of NO (～0.9 atm) (130–160°C) completely suppress AcH formation. k₁ = 10^16.2–40.9/θ sec^?1. Since (E₁ + RT) and ΔH°₁ are identical, within experimental error, both may be equated with D(s-BuO-NO) = 41.5 ± 0.8 kcal/mol and E₂ = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result ΔH°_f (s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}) = ? 16.6 ± 0.8 kcal/mol. From ΔS°₁ and A₁, k₂ is calculated to be 10^10.4 M^?1 · sec^?1, identical to that for TBN. From an independent observation that k₆/k₂ = 0.26 ± 0.01 independent of temperature, \documentclass{article}\pagestyle{empty}\begin{document}${\rm s - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}, we find E₆ = 0 ± 1 kcal/mol and k₆ = 10^9.8M^?1 · sec^?1. Under the conditions first cited, methyl ethyl ketone (MEK) is also a product of the reaction, the rate of which becomes measurable at extents of conversion >2%. However, this rate is ～0.1 that of AcH formation. Although MEK formation is affected by the ratio S/V for different reaction vessels, in a spherical reaction vessel, this MEK arises as the result of an essentially homogeneous first-order 4-centre elimination of HNO. \documentclass{article}\pagestyle{empty}\begin{document}${\rm SBN}\mathop \to \limits^{\rm 5} {\rm MEK} + {\rm HNO}$\end{document}; k₅ = 10^12.8–35.8/θ sec^?1. Sec-butyl alcohol (SBA), formed at a rate comparable to MEK, is thought to arise via the hydrolysis of SBN, the water being formed from HNO. The rate of disappearance of SBN, that is, d(MEK + SBA + AcH)/dt, is given by k_global = 10^15.7–39.6/θ sec^?1. In NO (～1 atm) the rate of formation of MEK was about twice that in the absence of NO, whereas the SBA was greatly reduced. This reaction was also affected by the ratio S/V of different reaction vessels. It was again concluded that in a spherical reaction vessel, the rate of MEK formation was essentially homogeneous and first order. This rate is given by k_obs = 10^12.9–35.4/θ sec^?1, very similar to k₅. However, although it is clear that the rate of formation of MEK is doubled in the presence of NO, the value for k_obs makes it difficult to associate this extra MEK with the disproportionation of s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document} and NO: s-\documentclass{article}\pagestyle{empty}\begin{document}$s{\rm - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}. NO at temperatures of 130–160°C completely suppresses AcH formation. AcH reappears at higher temperatures (165–200°C), enabling k_3c to be determined. Ignoring reaction (6), d(AcH)/dt = k₁k₃ (SBN )/[k_3c + k₂(NO)]; k_3c = 10^14.8–15.3/θ sec^?1. Inclusion of reaction (6) into the mechanism makes very little difference to the result. Reaction (3c) is expected to be a pressure-dependent process.     

Gas phase ion chemistry of methyl acetate,methyl propanoate and their enolic tautomers. An experimental approach

From a combination of isotopic substitution, time-resolved measurements and sequential collision experiments, it was proposed that whereas ionized methyl acetate prior to fragmentation rearranges largely into \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 \mathop {\rm C}\limits^ + ({\rm OH}){\rm O}\mathop {\rm C}\limits^{\rm .} {\rm H}_2 $\end{document}, in contrast, methyl propanoate molecular ions isomerize into \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^. {\rm H}_2 {\rm CH}_2 \mathop {\rm C}\limits^ + ({\rm OH}){\rm OCH}_3 $\end{document}. Metastably fragmenting methyl acetate molecular ions are known predominantly to form H₂?OH together with \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 - \mathop {\rm C}\limits^ + = {\rm O} $\end{document}, whereas ionized methyl propanoate largely yields H₃CO˙ together with \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm CH}_2 - \mathop {\rm C}\limits^ + = {\rm O} $\end{document}. The observations were explained in terms of the participation of different distonic molecular ions. The enol form of ionized methyl acetate generates substantially more H₃CO˙ in admixture with H₂?OH than the keto tautomer. This is ascribed to the rearrangement of the enol ion to the keto form being partially rate determining, which results in a wider range of internal energies among metastably fragmenting enol ions. Extensive ab initio calculations at a high level of theory would be required to establish detailed reaction mechanisms.     

Equilibrium sublimation and thermodynamic properties of SnSe and SnSe2

Knudsen effusion studies of the sublimation of polycrystalline SnSe and SnSe₂, prepared by annealing and chemical vapor transport reactions, respectively, have been carried out using vacuum microbalance techniques in the temperature ranges 736–967 K and 608–760 K, respectively. From experimental mass-loss data for the sublimation reaction SnSe(s) = SnSe(g), the recommended values for the heat of formation and absolute entropy of SnSe(s) were calculated to be ΔH°_298,f = ?86.4 ± 9.9 kJ · mol^?1 and S°₂₉₈ = 89.0 ± 7.1 J · K^?1 · mol^?1. From mass-loss data for the decomposition reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SnSe}_{\rm 2} ({\rm s)} = {\rm SnSe(s)} + \frac{1}{{\rm x}}{\rm Se}_{\rm x} ({\rm g) (x} = 2 - 8) $\end{document}, the recommended values for the heat of formation and absolute entropy of SnSe₂(s) were determined to be ΔH°_298,f = ?118.1 ± 15.1 kJ · mol^?1 and S°₂₉₈ = 111.8 ± 11.8 J · K^?1 mol^?1.     

Rate constants for self- and cross terminations of transient radicals in solution by effect modulated electron spin resonance spectroscopy

It is shown how electron spin resonance spectroscopy with modulated radical initiation can be used to analyze by purely spectroscopic means the second-order termination kinetics of systems containing two different kinds of radicals. The technique is applied to species generated by photoreduction of acetone in tetraethoxy silane. The bimolecular self- and cross reactions of \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm O)}_{\rm 3} {\rm SiO\dot CHCH}_{\rm 3} (\dot R_1 )\,and\,(CH_3 )_2 \dot COH(\dot R_2 )$\end{document} are found to be encounter-controlled processes. For the cross termination the often used relation k₁₂ = (4 k₁k₂)^1/2 is verified experimentally.