Temperature dependence of the reaction rate constants for O(3P) atoms with C2H4, C3H6 and NO(M = N2O), determined by a modulation technique

Rate constants for the reaction of O(³P) atoms with C₃H₄, C₃H₆ and NO(M = N₂O) have been measured over the temperature range 300–392°K using a modulation-phase shift technique. The Arrhenius expressions obtained are:C₂H₄, k₂ = 3.37 × 10⁹ exp[?(1270 ± 200)/RT]liter mole^?1 sec^?1,C₃H₆, k₂ = 2.08 × 10⁹ exp[?(0 ± 300)/RT]liter mole^?1 sec^?1,NO(M = N₂O), k₁ = 9.6 × 10⁹ exp[(900 ± 200/RT]liter² mole^?2 sec^?1.These temperature dependencies of k₂ are in good agreement with recent flash photolysis-resonance flourescence measurements, although lower than previous literature values.     

Rate constants for the reaction of OH radicals with CH3CN, C2H5CN AND CH2=CH-CN in the temperature range 298–424 K

Rate constants for the reactions of OH with CH₃CN, CH₃CH₂CN and CH₂=CH-CN have been measured to be 5.86 × 10⁻¹³ exp(−1500 ± 250 cal mole⁻¹/RT), 2.69 × 10⁻¹³ exp(−1590 ± 350 cal mole⁻¹/RT and 4.04 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles.     

Difluoro(aryl)(perfluoroalkyl)‐λ4‐sulfanes and Selanes: Missing Links of Trichloroisocyanuric Acid/Potassium Fluoride Chemistry

The TCICA/KF approach to oxidative fluorination of heteroatoms has emerged as a surprisingly simple, safe, and versatile surrogate to classically challenging fluorination reactions. Although polyfluorination (or chlorofluorination) of diaryl disulfides, diaryl diselenides, diaryl ditellurides, aryl iodides, and aryl(perfluoroalkyl)tellanes has been described, the application of this TCICA/KF methodology to aryl(perfluoroalkyl)sulfanes and selanes remains an area of unexplored chemical space. Accordingly, to address the “missing links” in the developing series of chalcogen‐based substrate reactivity, we report mild syntheses of metastable difluoro(aryl)(perfluoroalkyl)‐λ⁴‐sulfanes and selanes. As only limited examples of these species exist in the current literature (accessible only by using F₂ or XeF₂/HF), we have carried out detailed structural analyses, primarily using NMR and SC‐XRD data. In addition, we investigate the effect of the perfluoroalkyl chain on the outcome of oxidative fluorination, and, finally, we provide preliminary evidence that difluoro(aryl)(trifluoro‐methyl)‐λ⁴‐sulfanes may act as fluorinating reagents.     

Absolute rate constants for the reactions of O(3P) atoms and OH radicals with SiH4 over the temperature range of 297–438°K

Absolute rate constants for the reaction of SiH₄ with O(³P) atoms and OH radicals have been determined over the temperature range 297°–438°K using flash photolysis–NO₂ chemiluminescence and flash photolysis–resonance fluorescence techniques, respectively. The Arrhenius expressions obtained are where the error limits in the Arrhenius activation energies are the estimated overall error limits. Rate data for the reactions of SiH₄, CH₄, and H₂S with O(³P), H, and F atoms and with OH, CH₃, and CF₃ radicals are compared, showing that H₂S and SiH₄, which have similar bond energies, have reasonably similar reactivities toward these atoms and radicals.     

Kinetics of the reaction O(3P) + SO2 + M → SO3 + M over the temperature range of 299°–440°K

Rate constants for the reaction O(³P) + SO₂ + M have been determined over the temperature range of 299°–440°K, using a flash photolysis–NO₂ chemiluminescence technique. For M?Ar, the Arrhenius expression was obtained. At room temperature k₂^Ar = (1.05 ± 0.21) × 10^?33 cm⁶/molec²·sec. In addition, the rate constants k₂ = (1.37 + 0.27) × 10^?33 cm⁶/molec²·sec, k₂ = (9.5 ± 3.0) ± 10^?33 cm⁶/molec²·sec, k₃ = (1.1 ± 0.2) ± 10^?31 cm⁶/molec²·sec, and k₃ = (2.6 ? 0.9) ± 10^?31 cm⁶/molec²·sec were obtained at room temperature where k₃^M is the rate constant for the reaction O + NO + M → NO₂ + M. The rate data are compared and discussed with literature values.     

Proton nuclear magnetic resonance spectroscopy of normal and edematous brain tissue in vitro: Changes in relaxation during tissue storage

Proton nuclear magnetic resonance relaxation times, T₁ and T₂, of water in unfixed gray and white matter from normal and edematous rabbit brain tissues were measured in vitro at 23°C and 100 MHz to evaluate the effects of the temperature (?25°C to 37°C) and duration (0 to 96 h) of tissue storage on relaxation times. T₁ and T₂ tended to decrease during storage, probably from slow dehydration of the tissue. This effect was greatest in tissues stored at 37°C and least in those stored at 4 and ?25°C; decreases in T₁ and T₂ were greater in white matter than in gray matter. Freezing brain tissue to ?25°C caused a sudden decrease in the T₂ of normal white matter. Relaxation times were constant for 5 h in tissues stored at 23°C and for 40 h at 4°C. These results correlated well with corresponding tissue water loss.