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  • Physical Chemistry  (6)
  • [abr] Tris tris (hydroxymethyl) amino-methane
  • 1975-1979  (6)
Collection
Keywords
  • Physical Chemistry  (6)
  • [abr] Tris tris (hydroxymethyl) amino-methane
  • Chemistry  (6)
Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 9 (1977), S. 619-628 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 9 (1977), S. 743-749 
    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.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 10 (1978), S. 855-869 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This investigation presents a detailed examination of the relative reliability of the comparative and absolute rate methods as they are applied to kinetic studies in the single-pulse shock tube. For this purpose two previously studied reactions, the thermal elimination of HCl from ethyl chloride and n-propyl chloride, were selected and mixtures of these compounds were shock heated to temperatures in the range of 960°-1100°K. The experimental results were analyzed by both methods and the rate constants obtained from these analyses are compared with those of previous studies. The advantages and shortcomings of both methods are noted and it is concluded that reliable kinetic data can be obtained by the absolute rate (isolation technique) method with careful examination of the gas-dynamic flow conditions and taking cognizance of the incident shock deceleration. The limitations of the comparative rate technique encountered in the present study were similar to those detailed in previous investigations.
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 363-379 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The modified semi-ion pair model for four-center reactions initially developed to treat the addition of hydrogen halides to olefins, including polar olefins, has been extensively applied to these systems. In addition, the restriction that the species added be a hydrogen halide has been relaxed and addition of HOH to olefins is treated within the same frame-work. Input parameters, transition state properties, and calculated activation energies are presented for 111 such reactions. Calculated activation energies for the elimination reactions agree to better than ±2 kcal/mole, on the average, with experimental values where these areknown.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 649-660 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A semiempirical approach has been used to evaluate rate parameters for a three-center decomposition reaction from the point of view of transition state theory, with perfluorodiazirine serving as the prototype molecule. Several activated complex models are considered in which the reaction coordinate is chosen as the ∡ NCN bending mode. The constraints imposed include the principle of concerted bond-order conservation in passing from the initial to the final state, and use is made of empirical bond order-bond length and bond order-force constant relationships. The geometric configuration of the transition state sought is one which conforms with the lowest energy path and is also consistent with the observed entropy of activation. The potential energy of activation is taken as the optimum difference in binding energies (based on the INDO method) between the transition and initial states, and the critical energy is obtained by applying a correction for the zero-point energy difference, derived from normal coordinate analysis. Satisfactory agreement is found in the case of the activated complex model for which the total bond order is conserved and bonds undergoing rupture are assigned a fractional bond order (FBO) of 2/3, derived from the postulate (FBO) = α/β whe re α(=2) is the number of bonds breaking, and β(=3) is the number of bonds undergoing change in the ring opening.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 9 (1977), S. 697-703 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,1,1-Difluorochloroethane (Freon 142) was photolyzed at 147 nm in the pressure range of 3.6-20.6 torr. The effects of added NO, H2S, and CF4 were investigated. The extinction coefficient at 147 nm and 296°K was determined to be 64 ± 8 atm-1 · cm-1.The molecule photodecomposes largely by α,β elimination of HCl to give 1,1-difluoroethylene (Φ = 0.74 ± 0.06). There is no observable elimination of HF, but there is strong evidence for the elimination of the elements of FCl though the relative importance of this process is minor, as are contributions from carbon—carbon and carbon—halogen bond fission.The 1,1-difluoroethylene formed is undoubtedly vibratonally excited and is the source of a pressure-dependent small yield of fluoroacetylene. Over the pressure range studied there is no evidence that the major primary process itself is affected by changes in total pressure as is the case in the 147-nm photolysis of ethyl chloride.
    Additional Material: 1 Ill.
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