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  • Articles  (24)
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  • 1
    Electronic Resource
    Electronic Resource
    Structures, barriers for internal rotation, vibrational frequencies, and thermodynamic functions of CH2FCH2, CHF2CH2, and CF3CH2 radicals: An ab initio study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6620-6629 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometries, rotational barriers, and harmonic vibrational frequencies for β-fluoroethyl (CH2FCH2), β,β-difluoroethyl (CHF2CH2), and β,β,β-trifluoroethyl (CF3CH2) radicals have been determined by ab initio molecular-orbital techniques using the gaussian 86 system of programs at the unrestricted Hartree–Fock, UHF/6-31G* level of theory. Three conformational minima in the potential-energy surface were found for the CH2FCH2 and CHF2CH2 radicals, while only one was found for CF3CH2. The radical centers for all three species are nonplanar, but the effect on the geometries of these radicals in replacing β-position hydrogen by fluorine atoms is much weaker than is the case for α-position fluorine substituted ethyl radicals. Transition structures for internal rotation were also located. Estimates for the correction of electron correlation effects were obtained by single-point calculations using second-order Moller–Plesset perturbation theory (UMP2). The rotation about the C–C bond is almost free for all three radicals, which again is much different from the situation in the α-fluorine substituted ethyl radicals. Based on calculated vibrational frequencies and moments of inertia, thermodynamic properties including heat capacities, entropies, enthalpy, and free-energy functions are tabulated as a function of temperature. Several isodesmic–homodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation of the β-fluoroethyl and β, β-difluoroethyl radicals for which experimental values are not available. The theoretical heats of formation thus evaluated are −10.65 and −66.26 kcal/mol for CH2FCH2 and CHF2CH2, respectively. Together with the measured ΔH0f(CF3CH2), these data are used to evaluate ΔH0f,T, ΔG0f,T, and log Kf for all three radicals as a function of temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458929
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  • 2
    Electronic Resource
    Electronic Resource
    Structures, barriers for internal rotation and inversion, vibrational frequencies, and thermodynamic functions of CH2FCF2, CHF2CF2, and CF3CF2 radicals: An ab initio study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2774-2786 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometries, rotational and inversion barriers, and harmonic vibrational frequencies for α,α,β-trifluoroethyl (CH2FCF2), α,α,β,β-tetrafluoroethyl (CHF2CF2), and pentafluoroethyl (CF3CF2) radicals have been determined by ab initio molecular orbital techniques using the GAUSSIAN 86 system of programs at the unrestricted Hartree–Fock level of theory with the 6-31G* basis set (UHF/6-31G*). Three conformational minima in the potential energy surface were found for the CH2FCF2 and the CHF2CF2 radicals, while only one was found for the CF3CF2 radical. The radical centers for all three species are nonplanar. The barriers hindering rotation about the C–C bond and inversion of the radical center were located for each compound by analytical methods. Vibrational frequencies, as well as moments of inertia for overall and internal rotation are reported for each species. Calculated heat capacities, entropies, and free energy functions are tabulated as a function of temperature. Several homodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation of CH2FCF2 and CHF2CF2 radicals for which experimental values are not available. The theoretical heats of formation thus evaluated are −106.6 kcal/mol and −157.8 kcal/mol for CH2CF2 and CHF2CF2, respectively. These data and the experimental heat of formation of CF3CF2 (ΔH0f,298 =−213.0±1.3 kcal/mol) are used to evaluate ΔH0f ,T, ΔG0f ,T, and Kf ,T for all three radicals as a function of temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460928
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  • 3
    Electronic Resource
    Electronic Resource
    Structures, barriers for internal rotation and inversion, vibrational frequencies, and thermodynamic functions of CH2FCHF, CHF2CHF, and CF3CHF radicals: An ab initio study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7299-7310 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometries, rotational and inversion barriers, and harmonic vibrational frequencies for α, β difluoroethyl (CH2FCHF), α, β, β trifluorethyl (CHF2CHF), and α, β, β, β tetrafluoroethyl (CF3CHF) radicals have been determined by ab initio molecular orbital techniques using the gaussian 86 system of programs at the unrestricted Hartree–Fock (UHF)/6–31G* level of theory. Three conformational minima in the potential energy surface were found for the CH2FCHF, and CHF2CHF radicals, while only one was found for the CF3CHF radical. The radical centers for all three species are nonplanar. The barriers of rotation about the C–C bond and the inversion barriers of the radical center were located for each compound by analytical methods. Vibrational frequencies, as well as moments of inertia for overall and internal rotation are reported for each species. Calculated heat capacities, entropies, and enthalpy and free energy functions are tabulated as a function of temperature. Several isodesmic/homodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation of the three radicals for which experimental values are not available. The theoretical heats of formation (ΔH0f,298 ) thus evaluated are −56.3 kcal/mol, −108.0 kcal/mol, and −164.5 kcal/mol for CH2FCHF, CHF2CHF, and CF3CHF, respectively. These data are used to evaluate ΔH0f,T, ΔG0f,T, and Kf,T for all three radicals as a function of temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460214
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  • 4
    Electronic Resource
    Electronic Resource
    Structures, barriers for rotation and inversion, vibrational frequencies, and thermodynamic functions of ethyl, α-fluoroethyl, and α,α-difluoroethyl radicals: An ab inito study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1187-1195 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surfaces of CH3CHF and CH3CF2 radicals were studied by ab initio molecular orbital methods using the gaussian 〈size;8〉86〈size;10〉 system of programs at the UHF/6-31G* level of theory. CH3CHF has C1 symmetry and exists as a single pair of enantiomeric conformations. The difluoro species has only a single stable structure, of Cs symmetry. The barriers to rotation about the C–C bond, and the barriers hindering pyramidal inversion at the nonplanar radical center were located for each compound by analytical methods. The monofluoro and difluoro species had similar rotation barriers at the UMP2/6-31G*//6-31G* level, 1.68 and 2.26 kcal/mol, respectively, after inclusion of zero-point vibrational energy differences. The inversion barriers were substantially different, 0.54 and 10.45 kcal/mol, respectively. Vibrational frequencies, as well as moments of inertia for overall and internal rotations, are reported for each species and for the ethyl radical. Calculated heat capacities, entropies, enthalpies, and free energy functions are tabulated as a function of temperature. Use of several isodesmic or homodesmic reactions to obtain a value for the heat of formation of CH3CHF at 298 K is discussed. Good experimental values are available for ethyl and CH3CF2. Adopting reference values for ΔH0f,298 of 28.36, −17.3, and −72.3 kcal/mol for CH3CH2, CH3CHF, and CH3CF2, respectively, values for ΔH0f,T, ΔG0f,T and log10Kf for all three radicals are reported as a function of temperature in the range 0–1500 K. Comparison of the theoretical and experimental data for CH3CH2 suggests that the error introduced by use of harmonic HF/6-31G*//6-31G* frequencies is ±1 cal mol−1 K−1 for both heat capacity and entropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459182
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  • 5
    Electronic Resource
    Electronic Resource
    Reactions of ground state chlorine atoms with fluorinated methanes and ethanes (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 65-74 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactions of photochemically generated Cl(2PJ) atoms with a number of fluorohydrocarbons have been investigated in the temperature range 8–95 °C by the competitive photochlorination technique using CH4 as a primary standard. Relative and absolute rate parameters are reported for CH3F, CH2F2, CH3CH2F, CH2FCH2F, CH3CHF2, CH3CF3, CH2FCHF2, CHF2CHF2, and several auxiliary reactions including CH3Cl, C2H6, and C3H8. The internal competition for hydrogen abstraction in asymmetric fluorethanes is examined in detail. The reactivity trends are discussed and it is found that the activation energies in the fluoromethane series correlate with the known C–H bond dissociation energies. The hydrogen reactivity in the fluoroethane series for which a sufficient data base of DH°(C–H) values is not available is best rationalized in terms of inductive effects and resonance interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448737
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics of the thermal decomposition of CF3CHCL2 in a single-pulse shock tubeWork supported by the National Research Council of Canada. (1973)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 5 (1973), S. 363-373 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis of 2,2-dichloro-1,1,1-trifluoroethane was studied over the temperature range of 1120-1260°K at total reflected shock pressures from ∼2800 to 3100 torr. Below 1260°K, the decomposition leads to three reaction products which were identified as CF2CFCl, CF2CFH, and CF3CCl3. The results are interpreted in terms of a parallel C—Cl bond rupture process which becomes competitive with the molecular HCI elimination. The rate constant for the α,α-elimination process \documentclass{article}\pagestyle{empty}\begin{document}$$ CF_3 CHCl_2 \to CF_2 CFCl + HCL $$\end{document} has been deduced to be \documentclass{article}\pagestyle{empty}\begin{document}$$ \log \left( {K_1 ^\infty /\sec ^{ - 1} } \right) = \left( {13.4 \pm 0.7} \right) - \left( {63.1 \pm 3.8kcal} \right)/2.303RT $$\end{document} It was also possible to obtain the overall rate constant for the formation of CF2CFH, which is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log \left( {K^{''} /\sec ^{ - 1} } \right) = \left( {11.5 \pm 0.8} \right) - \left( {54.1 \pm 3.8kcal} \right)/2.303RT $$\end{document} Some evidence for hydrogen fluoride elimination was found at temperatures above 1260°K. However, at these higher temperatures C—C bond scission also occurs and the kinetics of the system become untractable.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550050307
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  • 7
    Electronic Resource
    Electronic Resource
    Hydrogen/deuterium abstraction by chlorine atoms from gaseous ethyl chlorides. Secondary kinetic isotope effects in the system CH3CH2Cl, CH3CHDCl, CH3CD2Cl (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 16 (1984), S. 621-631 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8-94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:The temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 /k_2 = (1.099 \pm 0.015)\exp [(429 \pm 2)/T] $$ $$ k_1 /k_r = (1.422 \pm 0.026)\exp [(1113 \pm 3)/T] $$ $$ k_2 /k_r = (1.295 \pm 0.029)\exp [(684 \pm 3)/T] $$ $$ k_3 /k_r = (1.177 \pm 0.025)\exp [(717 \pm 4)/T] $$ $$ k_4 /k_r = (1.115 \pm 0.023)\exp [(732 \pm 2)/T] $$ $$ k_5 /k_r = (0.978 \pm 0.020)\exp [(985 \pm 2)/T] $$\end{document} and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550160602
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  • 8
    Electronic Resource
    Electronic Resource
    Primary processes in the 147-nm photolysis of 1,1-dichloroethane (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 9 (1977), S. 619-628 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The room temperature photolysis of 1,1-dichloroethane at 147 nm in the pressure range of 1.34-196.2 torr is characterized almost entirely by the molecular elimination of HCl, Cl2, and small quantities of H2. Acetylene is also produced. While it is possible that the C2H2 arises, in part, from the decomposition of vibrationally excited ground states of C2H3Cl and/or C2H4, in this particlar case serious consideration has to be given to alternative explanations where the products of the primary processes are formed in electronically excited states. The ±, elimination of molecular chlorine is not inconsistent with an increased degree of Cl—Cl interaction predicted for a «Rydberg «state of 1,1-C2H4Cl2. Varying small yields of CH4 are observed in the presence and absence of NO. The effect of large pressures of CF4 on the quantum yields of the major products is extremely small. The extinction coefficient for 1,1-C2H4Cl2 at 147 nm and 296°K is 246 ± 29 cm-1 ± atm-1.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550090410
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  • 9
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet (147 nm) photolysis of 1,2-fluorochloroethane (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 9 (1977), S. 743-749 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8-20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm-1 · cm-1.The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10-10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbon—halogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550090505
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  • 10
    Electronic Resource
    Electronic Resource
    The Competitive dehydrohalogenation of 1,1,1-trifluoro-2-chloroethane in reflected shock wavesWork supported by the National Research Council of Canada. (1972)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 4 (1972), S. 559-571 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of 1,1,1-trifluoro-2-chloroethane has been investigated in the single-pulse shock tube between 1120° and 1300deg;K at total reflected shock pressures from ∼2610 to 3350 torr. Under these conditions, the major reaction is the α,α-elimination of hydrogen chloride, \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 3} {\rm CH}_{\rm 2} {\rm Cl}\mathop {{\rm \rightarrow}}\limits^{k_1 } {\rm CF}_{\rm 2} {\rm CHF} + {\rm HCl}$$\end{document} with \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log(}k_1^\infty {\rm, sec}^{ - {\rm 1}} {\rm) = 13}{\rm .3} \pm {\rm 0}{\rm .4} - (65.5 \pm 2.2{\rm kcal})/2.303RT$$\end{document} The decomposition also involves the slower α,β-elimination of hydrogen fluoride, \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 3} {\rm CH}_{\rm 2} {\rm Cl}\mathop {{\rm \rightarrow}}\limits^{k_2 } {\rm CF}_{\rm 2} {\rm CHCl} + {\rm HF}$$\end{document} with the first-order rate constant given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log(}k_2^\infty {\rm, sec}^{ - {\rm 1}} {\rm) = 12}{\rm .7} \pm {\rm 0}{\rm .5} - (67.6 \pm 2.7{\rm kcal})/2.303RT$$\end{document} At temperatures above 1270°K, two additional minor products were observed. These were identified as CF2CFCl and CF3CHCl2 and suggest C—Cl rupture as a third reaction channel leading to complicated kinetics.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550040510
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