Self- and cross-disproportionation-to-combination rations for cyclopentyl and cyclohexyl radicals and their deuterated analogues

Hydrogen, cycloalkene, and bicycloalkyl were found to be the principal products which account for ≈?97% of all products formed in the gas-phase radiolysis of water vapor containing low concentrations of cycloalkanes. From the ratios of cycloalkene-to-bicycloalkyl yields extrapolated to the zero dose, the self- and cross-disproportionation-to-recombination rate constant ratios Δ = k_d/k_c were determined for the following 12 reactions: Δ(c-C₅H₉, c-C₅H₉) = 0.73; Δ(c-C₅D₉, c-C₅D₉) = 0.58; Δ(c-C₆H₁₁, cC₆H₁₁) = 0.59; Δ(c-C₆D₁₁, c-C₆D₁₁) = 0.46; Δ(c-C₅H₉, c-C₆H₁₁) = 0.28; Δ(c-C₅D₉, c-C₆H₁₁) = 0.28; Δ(c-C₅H₉, c-C₆D₁₁) = 0.24; Δ(c-C₅D₉, c-C₆D₁₁) = 0.24; Δ(c-C₆H₁₁, c-C₅H₉) = 0.33; Δ(c-C₆H₁₁, c-C₅D₉) = 0.25; Δ(c-C₆D₁₁, c-C₅H₉) = 0.35; and Δ(c-C₆D₁₁, c-C₅D₉) = 0.28, where in the case of the cross-disproportionation the symbol Δ(R₁,R₂) is used to represent k_d/k_c for the disproportionation in which radical R₁ captures a hydrogen (deuterium) atom from radial R₂. The geometrical mean rule holds in the cross-combination reactions of cyclopentyl and cyclohexyl radicals. The kinetic isotope effect in the disproportionation reaction was determined as 1.24 ± 0.06.     

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.     

The reactions of some interstellar ions with benzene,cyclopropane and cyclohexane

The reactions of the cyclic molecules C₆H₆ (benzene), c-C₃H₆ (cyclopropane) and c-C₆H₁₂ (cyclohexane) with ArH⁺ (ArD⁺), H₃⁺, N₂H⁺, CH₅⁺, HCO⁺, OCSH⁺, C₂H₃⁺, CS₂H⁺ and H₃O⁺ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C₂H₃⁺ proceed via proton transfer and all are fast except the H₃O⁺ and CS₂H⁺ reactions with c-C₆H₁₂ which are endothermic and which establish that the proton affinity of c-C₆H₁₂ is 160 ± 1 kcal mol⁻¹, which is considerably lower than the published value. In the c-C₃H₆ and the c-C₆H₁₂ reactions multiple products are observed and hence “breakdown curves” for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C₂H₃⁺ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.     

Energy transfer studies from excited cyclobutane chemically activated by nuclear recoil reaction

Relative vibrational energy transfer efficiencies are determined for cyclobutane-t chemically activated to an average energy of 5 eV by recoil tritium replacement reaction. The pressure and composition dependence of the stabilization-decomposition ratio indicates relative efficiencies of 1.00, 1.05, and 0.32 for c-C₄H₈, CF₄, and Ne bath gases.     

The Wall Effect on Hydrogen Formation in the Vapour-Phase Radiolysis of c-C6D12 and n-C7D16

Vapour-phase radiolysis of c-C₆D₁₂ and n-C₇D₁₆ leads to a relatively large HD yield, up to ～ 20% of the total hydrogen, which cannot be accounted for by incomplete deuteration of c-C₆D₁₂ and n-C₇D₁₆. In order to elucidate the mechanism of the HD formation, we have examined the effect of additives and of physical conditions on the HD yield. By coating the vessel with a layer of Aquadag the HD yield is greatly decreased without appreciable variation of the total hydrogen yield. The HD yield from nontreated vessels also decreases remarkably with increasing total dose; it is increased upon the addition of traces of water; and is less affected by small amounts of c-C₆H₁₂. The addition of SF₆ selectively reduces the HD yield. These experimental results lead us to conclude that inert hydrocarbon ions react by proton transfer with water desorbed from the vessel wall to give hydronium ions which yield HD on subsequent neutralization.     

An investigation of the decomposition of the common intermediate ions produced by electron impact. IV—[C6H5CO]+ ions from several alkyl benzoates

The decomposition of the [C₆H₅CO]⁺ ions produced from eight alkyl benzoates by electron impact has been studied. By calculating the heat of formation of [C₆H₅CO]⁺ ions from the appearance potential value, it is shown that the ions from C₆H₅COOR when R?H, CH₃, C₂H₅ have some excess energy, and those where R = n-C₃H₇, iso-C₃H₇, n-C₄H₉, iso-C₄H₉, iso-C₅H₁₁ are produced with more excess energy. It is also shown that by taking this excess energy into account, there is a linear relationship between the heat of formation of the activated complex produced in the reaction [C₆H₅CO]⁺→[C₆H₅]⁺ + CO and the vibrational degree of freedom of the neutral fragment ? OR.     

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.     

Vibrational energy transfer in cyclopropane (C3H6)

Infrared laser-induced fluorescence measurements of vibrational relaxation in cyclopropane are presented. Following laser excitation of the CH-stretch vibrations υ₆ and υ₈ time-dependent fluorescence signals from υ₁₀ and υ₇/υ₁₁ were recorded. Activation and deactivation rate constants for C₃H₆C₃H₆ collisions were found for υ₁₀ and υ₇/υ₁₁. A simplified model for the vibrational relaxation of cyclopropane is discussed.     

Alkane loss from collisionally activated alkylmethyleneimmonium ions

The collision-induced dissociation (CID) spectra of five alkylmethyleneimmonium ions (H₂C-N⁺R¹R², (a) R¹ = R² = C₂H₅, (b) R¹ = n-C₃H₇, R² = H, (c) R¹ = n-C₃H₇, R² = CH₃, (d) R¹ = n-C₃H₇, R² = C₂H₅, (e) R¹ = R² = n-C₃H₇) are reported and discussed in terms of the mechanism of alkane loss. The most abundant alkane losses result from 2-azaallylic bond cleavages within R¹ and R² leading to daughter ions of m/z 84. Ion d (R¹ = n-C₃H₇, R² = C₂H₅) was chosen for a deuterium-labelling study because it exhibited methane loss nearly free from interferences with other fragmentations. The methane lost consists to a great extent (95%) of the methyl moiety of R². Whereas the methyl moiety obviously stays intact during the fragmentation process, the hydrogen additionally needed originates from all positions of R¹ and the double-bonded methylene in an approximately random distribution, suggesting extensive hydrogen migrations preceding the transfer step.     

Achieving strictly linear polyethylenes by the NNN-Fe precatalysts finely tuned with different sizes of ortho-cycloalkyl substituents

Six examples of newly synthesized α,α’-bis (aryl)-2,3:5,6-bis (pentame thylene)pyridyliron complexes [2,3:5,6-{C₄H₈C(NAr)}₂C₅HN]FeCl₂ (Ar = 2-(c-C₅H₉)-6-MeC₆H₃ Fe1 , 2-(c-C₆H₁₁)-6-MeC₆H₃ Fe2 , 2-(c-C₈H₁₅)-6-MeC₆H₃ Fe3 , 2-(c-C₅H₉)-4,6-Me₂C₆H₂ Fe4 , 2-(c-C₆H₁₁)-4,6-Me₂C₆H₂ Fe5 , 2-(c-C₈H₁₅)-4,6-Me₂C₆H₂ Fe6 ; c refers as cyclic), on activation with methylalumoxane (MAO) or modified MAO (MMAO), exhibit high activities towards ethylene polymerization, producing strictly linear polyethylenes with terminal vinyl groups. The catalytic performances are systematically investigated along with various polymerization parameters as well as the microstructures of resultant polyethylenes. The steric hindrances of ortho-cycloalkyl substituents of N_imino-aryl groups significantly affect the activities of the corresponding iron precatalysts as well as the microstructures of resultant polyethylenes: higher steric hindrance the ortho-cycloalkyl substituents, higher activity the iron precatalyst, lower molecular weight the resultant polyethylenes. Experimental observations are additionally supported by the computational study. The resultant polyethylenes exhibited excellent hydrophobicity.     

Isothermal phase equilibria for the (xenon + cyclopropane) mixed-gas hydrate system

Isothermal three-phase equilibria of gas, aqueous, and hydrate phases for the {xenon (Xe) + cyclopropane (c-C₃H₆)} mixed-gas hydrate system were measured at two different temperatures (279.15 and 289.15) K. The structural phase transitions from structure-I to structure-II and back to structure-I, depending on the mole fraction of guest mixtures, occur in the (Xe + c-C₃H₆) mixed-gas hydrate system. The isothermal pressure–composition relations have two local pressure minima. The most important characteristic in the (Xe + c-C₃H₆) mixed-gas hydrate system is that the equilibrium pressure–composition relations exhibit the complex phase behavior involving two structural phase transitions and two homogeneous negative azeotropes. One of two structural phase transitions exhibits the heterogeneous azeotropic-like behavior.     

Temperature Dependence of the Ratios of C—H (C—D) Bond Breaking Rates in Reactions of Cycloalkanes C5H10, C6H12, C6D12 with Adamantyl Carbocations in Sulfuric Acid

We have determined the differences in the parameters log A and E of the Arrhenius equations for the kinetic isotope effect (KIE) (c-C₆H₁₂/c-C₆D₁₂) and the 5/6 effect (c-C₅H₁₀/c-C₆H₁₂) in reactions of the C—H bonds of cycloalkanes with adamantyl (Ad⁺) carbocations (1-adamantanol in 92.8% H₂SO₄, 40-97 °C). We have established the compensation relations between log A and E for the kinetic isotope effect and the 5/6 effect for anthracene (AH⁺), hydroxymethyl (CH₂OH⁺), Ad⁺ carbocations and the hypothetical "infinitely strong reagent," supporting a hydride transfer mechanism in such reactions.     

A NEW PERSPECTIVE ON VANADYL TARTRATE DIMERS. PART II. STRUCTURE AND SPECTROSCOPIC PROPERTIES OF CALCIUM VANADYL TARTRATE TETRAHYDRATE

Abstract

The calcium vanadyl tartrate complex [Ca(VO)(d,l-C₄H₂O₆)(H₂O)₄] has been synthesized and characterized by spectroscopic methods. Its crystal structure was solved by X-ray methods. The compound is monoclinic, space group P2₁/c, with a = 8.0282(5), b = 17.1568(8), c = 7.6113(3)Å, β = 94.269(4)° and Z = 4. The structure consists of centrosymmetric vanadyl tartrate dimers, [(VO)(d,l-C₄H₂O₆)]₂ ^4-, and calcium cations placed between them. As a result, dimers form chains in the [101] direction. Neighbouring chains are linked by the coordination of the calcium ion to the oxygen atom of a vanadyl group of a different chain, thus forming a two-dimensional structure. Different layers are linked by hydrogen bonds. Spectroscopic studies show the existence of intra-dimeric interactions between vanadium atoms.     

The mechanism of ethylene pyrolysis at small conversions

Kinetic modelling is used in conjunction with measurements of product yields to develop a mechanism for the pyrolysis of ethylene at 896K and ethylene pressures ranging from approximately 3 to 78 kPa. An induction period was observed for all products except H₂, and was followed by a steady rate, which was of second-order for all products except 1,3-C₄H₆, the most abundant product. The mechanism quantitatively accounts for the yields of H₂, CH₄, C₂H₆, C₃H₆, 1-C₄H₈ and 1,3-C₄H₆. The reaction is initiated by disproportionation of C₂H₄ and the product 1,3-C₄H₆ results from decomposition of the C₄H₇ radical, formed by addition of C₂H₃ to C₂H₄. The other organic products that were measured are formed as a result of reactions involving the C₂H₅ radical. The hydrogen is produced by abstraction from C₂H₄ by atomic hydrogen and its rate is controlled by the reaction C₂H₅ → C₂H₄ + H which is nearly equilibrated. The main termination reaction is recombination of C₂H₅. The auto-acceleration which is evident particularly in the yields of H₂, CH₄, C₂ H₆, and C₃H₆ is accounted for by the decomposition of 1-C₄H₈. © 1996 John Wiley & Sons Inc.     

Gas-chromatographic determination of impurities of organic and chlorinated organic compounds and carbon monoxide and dioxide in high-purity hydrogen chloride

A gas-chromatographic procedure was developed for determining impurities (CH₄, C₂H₆, C₃H₈, C₄H₁₀, iso-C₄H₁₀, C₅H₁₂, iso-C₅H₁₂, neo-C₅H₁₂, CH₃Cl, C₂H₅Cl, CH₂Cl₂, CHCl₃, CO, and CO₂) in hydrogen chloride using two columns and a column switching technique in an isothermal mode with a flame ionization detector; the detection limits were 0.01–0.1 ppm. The matrix was separated in a precolumn packed with urea. CO and CO₂ were determined by reaction gas chromatography with their conversion into methane.     

Quenching of I(2P½) by R-OH compounds. Influence of the alkyl group on the quenching efficiency

The deactivation of I(²P_½) by R-OH compounds (R = H, C_nH_2n+1) was studied using time-resolved atomic absorption at 206.2 nm. The second-order quenching rate constants determined for H₂O, CH₃OH, C₂H₅OH, n-C₃H₇OH, i-C₃H₇OH, n-C₄H₉OH, i-C₄H₉OH, s-C₄H₉OH, t-C₄H₉OH, are respectively, 2.4 ± 0.3 × 10⁻¹², 5.5 ± 0.8 × 10⁻¹², 8 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 11.1 ± 0.9 × 10⁻¹², 9.8 ± 0.9 × 10⁻¹², 7.1 ± 0.7 × 10⁻¹², and 4.1 ± 0.4× 10⁻¹² cm³ molec⁻¹ s⁻¹ at room temperature. It is believed that a quasi-resonant electronic to vibrational energy transfer mechanism accounts for most of the features of the quenching process. The influence of the alkyl group and its role in the total quenching rate is also discussed. © 1997 John Wiley & Sons, Inc.     

Density functional complete study of hydrogen bonding between the water molecule and the hydroxyl radical (H2O · HO)

The hydrogen bonding complexes formed between the H₂O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6‐311++G(2d,2p) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6‐311++G(2d,2p). The two degenerate components of the OH radical ²Π ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H₂O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H₂O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H₂O · OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H₂O · HO system. Among them, four genuine minima were located. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Reactions of fluorine atoms with iodides studied by crossed beam laser-induced fluorescence

The reactions of F atoms with C₂H₅I, C₂F₅I, and n-C₃H₅I were studied by the crossed beam laser-induced fluorescence techniques within the 570–620 nm wavelength region. The vibrational and rotational excitation spectra of the reaction product IF were measured. The relative vibrational population densities of v = 3,4, and 5 vibrational levels, and some of the relative detailed vibrational rate constants, the rotational temperatures, and the mean fractions of rotational energy in individual vibrational states of the reaction product IF were obtained. The reaction mechanism was discussed.     

Permeation,diffusion, and solution of cyclopropane in silicone rubber

Permeability, solubility, and diffusion coefficients have been determined for cyclopropane (c-C₃H₆) in silicone rubber at temperatures between ?8 and 70°C at relative pressures from 0.04 to 0.30. The permeability coefficients, , are of the order of 10^?6 cm³ (STP) · cm/(s · cm² · cmHg). increases slightly with increasing penetrant pressure and decreases with increasing temperature, the energy of activation for permeation being ?1.27 kcal/gmol at zero pressure. The solubility of cyclopropane in silicone rubber can be represented over the experimental concentration range by the Flory-Huggins equation. The solubility decreases with increasing temperature and the partial molar heat of solution is ?4.95 kcal/gmol. The solubility coefficient in the Henry's law limit, S(0), for cyclopropane and many other gases and vapors can be correlated with (T_c/T)², where T and T_c are the experimental and critical temperatures, respectively. The mutual diffusion coefficients, D, increase with increasing concentration and temperature, the energy of activation for diffusion being 3.68 kcal/gmol. The pressure dependence of &\[\bar P\] is described satisfactorily by a free-volume model proposed by Fujita and extended by Stern, Frisch, and coworkers. The permeability, diffusion, and solubility behavior of cyclopropane in silicone rubber is similar to that of propane (C₃H₈).     

Transition-metal mediated heteroatom removal by reactions of FeL+ [L=O,C4H6, c-C5H6, c-C5H5, C6H6, C5H4(=CH2)] with furan,thiophene, and pyrrole in the gas phase

Reactions of Fe⁺ and FeL⁺ [L=O, C₄H₆, c-C₅H₆, C₅H₅, C₆H₆, C₅H₄(=CH₂)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe⁺, Fe(C₅H₅)⁺, and FeC₆H ₆ ⁺ yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺], as well as FeC₅H₄(=CH₂)⁺ and FeO⁺, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC₄H₆ ⁺, Fe(c-C₅H₆)⁺, and FeC₅H₄(=CH₂)⁺. In addition, FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C₅H₆)⁺ with pyrrole and thiophene is hydrogen-atom displacement, which implies D^O(Fa(N₅H₅)⁺-C₄H₄X)>D^O(Fe(C₅H₅)⁺-H)=46±5 kcal mol^?1. D^O(Fe⁺-C₄H₄S) and D^O(Fe⁺-C₄H₅N)=D^O(Fe⁺-C₄H₆)=48±5 kcal mol^?1. Finally, 55±5 kcal mol^?1=D^O(Fe⁺-C₆H₆)>D^O(Fe⁺-C₄H₄O)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mol^?1. FeO⁺ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D^O(Fe⁺-CS)>D^O(Fe⁺-C₄H₄S)≈48±5 kcal mol^?1 and D^O(Fe⁺-C₄H₅N)≈48±5 kcal mol^?1>D^O(Fe⁺-HCN)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mil^?1.