Unimolecular decomposition of chemically activated methylallylether

The unimolecular decomposition of chemically activated methylallylether (MAE) formed by the cross combination of methoxymethyl and vinyl radicals was studied in the gas phase. The experimentally determined rate constant was found to be 1.11 × 10⁸ sec^?1 at 9.6°C for the decomposition of MAE into propene and formaldehyde. The decomposition of MAE via the six-center retro-“ene” type transition state is analyzed by using the RRKM unimolecular reaction theory. For the molecular parameter assignments of energized MAE, a model which contains one internal rotational mode is supported, and MAE decomposition is characterized by a tight complex model. The best agreement between experimental and theoretical results was found when a critical energy of 40.1 kcal/mol was used.     

A relation between ion structures and experimental overall cross-sections for collisionally activated decomposition

Collisionally activated dissociation (CAD) mass spectra sometimes appear to be identical in spite of the fact that the precursor ion structures are known to differ. It is shown that determination of the experimental overall cross-section for collisionally activated decomposition yields valuable extra information. After applying it to examples of known structure, [C₄H₅N]^+·, [C₅H₅N]^+· and [C₅H₅O]⁺, it is used to study a more complex problem, that of [C₆H₆]^+· ions from four isomeric precursors.     

The unimolecular decomposition and isomerization of chemically activated 1-methyl-2,2,3,3-tetrafluorocyclopropane

The reaction of CH₂(¹A₁) with 1,1,2,2-tetrafluorocyclopropane was studied at 300 K and at pressures between 9.0 and 365.0 torr. Chemically activated 1-methyl-2,2,3,3-tetrafluorocyclopropane was formed and two competitive reaction paths, namely decomposition and isomerization, were observed. By fitting the experimental results to calculated values from RRKM theory, we estimated the Arrhenius parameters for both reaction processess as well as the heat of formation of 1-methyl-2,2,3,3-tetrafluorocyclopropane. © John Wiley & Sons, Inc.     

Comparison between HPGe and CdZnTe detector for the correlation between calculated radioactivity and measured dose using an activated concrete sample

An activated concrete sample was counted at different source to detector distances with CdZnTe and HPGe detectors. The experimental count rates for different radionuclides were converted to dose rate using Monte Carlo code and compared with the Measured dose rates obtained using digital survey meter. The results agreed well for both the detectors. This indicates that CdZnTe detector having a better portability but poorer resolution than HPGe detector can be effectively used for online monitoring of radioactivity as well as dose rate calculations.     

The decomposition kinetics of chemically activated methyl-d1-methylsilane-d2 and ethylsilane-d3

The decomposition kinetics of chemically activated methyl-d₁-methylsilane-d₂ (DMS-d) and ethylsilane-d₃ (ES-d) from the Si-D and C-H insertion reactions of CH₂ (¹A₁) with methylsilane-d₃ have been studied. The total rate constants for decomposition of chemically activated DMS-d₃ and ES-d₃ have been measured. The individual rate constants for molecular elimination of CH₃D, CH₂D₂, and D₂ from DMS-d and for molecular elimination of CH₃CH₂D and D₂ from ES-d have been measured. All of the above rate constants exhibit the expected kinetic isotope effect when compared to those found previously in the undeuterated system. RRKM theory calculations of the rate constants for the expected C-Si and Si-D bond rupture processes, based on energetics and activated comple× models deduced previously for the undeuterated system, were carried out. In the case of DMS-d the RRKM theory calculations of rate constants for the bond rupture processes combined with experimental rate constants for the molecular elimination processes gave a total rate constant for decomposition in agreement with the measured value. The results of a high-pressure study of the CH₃D/CH₂D₂ ratio from chemically activated DMS-d₃ decomposition were consistent with complete randomization of internal energy up to a pressure of 4 atmospheres (lifetime of ～1.7 × 10^×11 sec). This is not an unexpected result in light of earlier work.     

Comparison of ab initio calculated and experimental methyl-top moments of inertia

The methyl-top moments of inertia and planar moments of inertia of a large number of compounds have been obtained from rotational spectroscopic data and are compared with the corresponding quantities obtained from ab initio geometries. Ab initio geometry refinements have been performed with the 4-21G basis set using standard gradient techniques. High correlation is found between the spectroscopic and calculated values, indicating the possibility of using experimental methyl-top moments of inertia as a source of structural information on methyl groups.     

Comparison of calculated and experimental FTIR spectra of specifically labeled ubiquinones

Density functional theory has been used to calculate harmonic vibrational frequencies and intensities of unlabeled and labeled ubiquinone-1 in both the gas phase and in solution (CCl₄). Calculations were undertaken using the B3LYP functional and the 6-31G+(d) basis set. Calculations using larger basis sets did not significantly alter the calculated spectra. Calculations for ubiquinone-2, -3, -6 or -8 gave similar results.Calculations show that eight ubiquinone-1 conformations, which differ only in the orientation of their methoxy groups, are likely to coexist in solution at room temperature. The calculated infrared spectra for these eight conformations vary considerably. However, by averaging the Boltzmann weighted spectra for the eight conformers, composite spectra are calculated that successfully model both the frequency and intensity information inherent in the experimental FTIR spectra obtained for both unlabeled and labeled ubiquinones in solution.The calculated spectra presented here provide a robust foundation from which to consider and assess future modeling of the vibrational properties of ubiquinones embedded in protein complexes.     

Non-RRKM decomposition of chemically activated radicals: Reaction of fluorine atoms with tetraallyl germanium

Thermal F atoms react with gaseous (CH₂CHCH₂)₄Ge to produce CH₂CHF through dissociation of the (CH₂CHCH₂)₃-GeCH₂CHFCH₂^* radical. The rapid decomposition is attributed to non-RRKM behavior with excitation energy largely confined to the CH₂CHFCH₂ side group. The central atoms mass effect found in linear seven-atom trajectory calculations has not yet appeared in (CH₂CHCH₂)₄M with the replacement of Sn by Ge.     

Formation and decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction

The formation and the decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction have been studied in the gas phase at room temperature. Two different experimental arrangements have been used. Arrangement A consisted of a laser-flash photolysis set up combined with quantitative Fourier transform infrared spectroscopy and allowed the determination of the stable products at 4 mbar. The c-C5H9 radicals were produced via the reaction c-C5H10 + Cl with chlorine atoms from the photolysis of CFCl3; the O atoms were generated by photolysis of SO2. Arrangement B, a conventional discharge flow-reactor with molecular beam sampling, was used to determine the rate coefficient. Here, the hydrocarbon radicals (c-C5H9, C2H5, CH2OCH3) were produced via the reaction of atomic fluorine with c-C5H10, C2H6, and CH3OCH3, respectively, and detected by mass spectrometry after laser photoionization. For the c-C5H9 + O reaction, the relative contributions of intermediate formation (c-C5H9O) and direct abstraction (c-C5H8 + OH) were found to be 68 +/- 5 and 32 +/- 4%, respectively. The decomposition products of the chemically activated intermediate could be identified, and the following relative branching fractions were obtained: c-C5H8O + H (31 +/- 2%), CH2CH(CH2)2CHO + H (40 +/- 5%), 2 C2H4 + H + CO (17 +/- 5%), and C3H4O + C2H4 + H (12 +/- 5%). Additionally, the product formation of the c-C5H8 + O reaction was studied, and the following relative yields were obtained (mol %): C2H4, 24%; C3H4O, 18%; c-C5H8O, 30%; c-C5H8O, 23%; 4-pentenal, 5%. The rate coefficient of the c-C5H9 + O reaction was determined relative to the reactions C2H5 + O and CH3OCH2 + O leading to k = (1.73 +/- 0.05) x 10(14) cm3 mol(-1) s(-1). The experimental branching fractions are analyzed in terms of statistical rate theory with molecular and transition-state data from quantum chemical calculations, and high-pressure limiting Arrhenius parameters for the unimolecular decomposition reactions of C5H9O species are derived.     

Comparison of experimental and calculated relative sensitivity coefficients for spark-source mass-spectrometry of metals

Sensitivity calibration has been performed for the spark-source mass-spectrometric analysis of iron, copper and aluminium matrices, with standard reference materials. The experimental relative sensitivity coefficients, corrected for discrimination effects in the mass spectrometer, are compared with values obtained with various empirical approaches to calculate relative sensitivity coefficients for an r.f. spark. The best correlation found is only of the order of 50%.     

Comparison of quantum mechanical and experimental gas-phase basicities of amines and alcohols

A comparison was made between the experimental and B3LYP relative gas-phase basicities and proton affinities of a series of 9 amine, 3 alcohol, and 3 alkanolamine molecules. While agreement is good for most of the species studied, it is poor for the alkanolamines and 1,2-ethanediol. A series of calculations were undertaken at the B3LYP and MP2 levels using various basis sets to see if the uncertainties in the calculations can account for the discrepancies. The results suggest that this is unlikely and that the theoretical values are likely to be reasonably accurate. Calculations are also presented for the dimer formation energies of alkanolamine molecules, diamine molecules, and 1,2-ethanediol. These calculations suggest that all of these species can form proton-bound dimers. The alkanolamines and 1,2-ethanediol also appear to have relatively high formation energies for neutral dimers.     

Paramagnetic species on the surface of chemically activated silica

Active centers of SiO₂ formed during thermolysis of methoxylated silica surface has been studied by ESR. Several types of coordinatively unsaturated silicon atoms, which differ in location and number but show similar reactivity toward various adsorbates, have been found.

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, . - , , , H₂, CO, O₂.

     

Kinetics of chemically activated ethane

Chemically activated ethane, with an excitation energy of 114.9 ± 2 kcal/mole, was formed by reaction with methane of excited singlet methylene radicals produced by the 4358 Å photolysis of diazomethane. A decomposition rate constant of (4.6 ± 1.2) × 10⁹ sec^?1 was measured for the chemically activated ethane. This result agrees, via RRKM theory, with most other chemically activated ethane data, and the result predicts, via RRKM and absolute rate theory for E₀ = 85.8 kcal/mole, E* = 114.9 kcal/mole, and k_E = 4.6 × 101 sec^?1, a thermal A-factor at 600°K of 10^16.6±0.2 sec^?1, in approximate agreement with the more recent experimental values. Combining 2 kcal/mole uncertainties in E₀ and E* with the uncertainty in our rate constant yields an A-factor range of 10^16.6±0.7 sec^?1. It is emphasized that this large uncertainty in the A-factor results from an improbable combination of uncertainty limits for the various parameters. These decomposition results predict, via absolute rate theory (with E₀(recombination) = 0) and statistical thermodynamic equilibrium constants, methyl radical recombination rates at 25°C of between 4.4 × 10⁸ to 3.1 × 10⁹ l.-mole^?1-sec^?1, which are 60 to 8 times lower, respectively, than the apparently quite reliable experimental value. A value of E₀(recombination) greater than zero offers no improvement, and a value less than zero would be quite unusual. Activated complexes consistent with the experimental recombination rate and E₀(recombination) = 0 greatly overestimate the experimental chemical activation and high pressure thermal decomposition rate data. Absolute rate theory as it is applied here in a straightforward way has failed in this case, or a significant amount of internally consistent data are in serious error. Some corrections to our previous calculations for higher alkanes are discussed in Appendix II.     

Aerobic oxidation of primary alcohols in the presence of activated secondary alcohols

Chemoselective aerobic oxidation of primary alcohols in the presence of activated secondary alcohols was effected under irradiation of visible light by using (nitrosyl)Ru(salen) complex 6 that possesses bulky 1-ethyl-1-methylpropyl groups at C3, C3′, C5 and C5′, as catalyst. For example, oxidation of n-decanol was >50 times faster than oxidation of 1-phenylethanol at 10 °C.     

Kinetic study of chemically activated chlorocyclopropane

Chlorocyclopropane has been produced by addition of CH₂(¹A₁) and CH₂(³B₁) to chloroethene. CH₂ was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3-chloropropene, cis- and trans-1-chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.     

Relationship between gas chromatographic behaviour and topological, physicochemical, and quantum chemically calculated charge parameters for neuroleptica

Gas chromatographic retention indices for a number of neuroleptic drugs on an apolar phase, OV-101, and a polar phase, OV-17, are correlated with parameters describing various properties of the separated molecules. The gas chromatographic behaviour is related to the same parameters as those used in quantitative structure activity relationships. The molecular connectivity indices and log k' in a reversed-phase HPLC system were chosen as parameters describing the apolar interactions of the molecules with the stationary phase. As properties involved in more specific interactions, and related to the presence of overall or local polarity, the molecular dipole moment and the charge on the N-atom were selected and quantum chemically calculated. It is found that the retention indices on the apolar phase, OV-101, can be successfully correlated with molecular connectivity indices, which are also used in QSAR studies. The retention indices on OV-17 show a high correlation with the charge on the N-atom. Evidence of the importance of this N-atom in pharmacological activity is known.     

Thermal decomposition of p-benzoquinone-diazides in alcohols and acids

Conclusions The thermal decomposition of p-benzoquinone-diazides in alcohols and acids has led to the formation of the corresponding hydroquinone ethers and esters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 961–963, April, 1969.The authors thank N.M. Émanuel for attention to the work in the process of its execution.     

Isomerization of chemically activated secondary butyl radical

Photolytic decomposition of hydrogen sulfide followed by the addition of energized hydrogen atoms to cisbut-2-ene gives excited sec-butyl radicals. The radicals undergo a 1,3 hydrogen migration as is evidenced by the good agreement between the RRKM calculations and experiment. The contribution of a 1,2 hydrogen shift cannot be excluded. The threshold energies are 153.8 and 176.8 kJ mol^–1 for 1,3 and 1,2 isomerization, respectively.

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-2 .- . 1,3- , . , 1,2- . 153,8 176,8 / 1,3- 1,2-, .