Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10?12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2-methylbutane, 3.97 ± 0.11; 2,2-dimethylbutane, 2.66 ± 0.08; 2-methylpentane, 5.68 ± 0.24; 3-methylpentane, 5.78 ± 0.11; 2,2,3-trimethylbutane, 4.21 ± 0.08; 2,4-dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3-tetramethylbutane, 1.06 ± 0.08; and 2,2,4-trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2-dimethylbutane, 2,4-dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature. 相似文献
Absolute rate constants are reported for reactions of C2O(3Σ?) under pseudo-first-order decay conditions. C2O is generated by laser photodissociation of C3O2 at 266 nm, and detected by dye-laser induced fluorescence on the 3Πi-3Σ? transition. Rate constants of (433 ± 12), (3.30 ± 0.12) and (1.12 ± 0.05) × 10?13 cm3 molecule?1 s?1 are reported for reactions with NO, O2 and isobutene. The NO value is approximate due to an apparent dark reaction between NO and C3O2. Upper limits of 1 × 10?14 cm3 molecule?1 s?1 are reported for reactions with H2, CO2, C3H2 and C2H4. The C2O + C3O2 reaction does not follow pseudo-first-order decay kinetics. Two explanations are proposed to explain this observation. Results are compared with previous relative rate measurements and are discussed in terms of their relevance to combustion chemistry. 相似文献
We report the first spectroscopic evidence for a [C?F?C]+ fluoronium ion in solution. Extensive NMR studies (19F, 1H, 13C) characterize a symmetric cage‐like species in which fluorine exhibits substantial covalent bonding to each of the two carbon atoms involved in the three‐center interaction. Experimental NMR data comport well with calculated values to lend credence to the structural assignment. As the culminating experiment, a Saunders isotopic perturbation test confirmed the symmetric structure. Congruent with the trend in other types of onium ions, the calculated charge at fluorine moves in a more positive (less negative) direction from the neutral. It is this important trend that explains in part the extraordinary historical difficulty in making theoretical predictions of fluoronium ions come true in solution, and why it takes fluorine captured in a cage to produce, finally, a stable ion and complete the historical arc of the organic halonium ion story. 相似文献
The decay of pernitric acid (HO2NO2) in the presence of excess nitric oxide has been studied in a 5800-liter, Teflon-lined chamber over the temperature range 254 to 283 K at 1 atm pressure of N2 by Fourier transform infrared spectroscopy. A heterogeneous reaction of NO2 and H2O2 was used to generate HO2NO2 with less than 20% HNO3 and less than 5% NO2 present as impurities. The HO2NO2 had lifetimes of 5 to 20 h in our chamber, presumably determined by heterogeneous loss to the walls. Two paths have been proposed for the reaction of NO2 with HO2: (1), NO2 + HO2 → HONO + O2 (2). In this study the ratio k1/k2 was calculated to be greater than 103 throughout the temperature range studied. The homogeneous unimolecular decay of the HO2NO2, reaction (3), was investigated by adding excess NO in order to remove HO2 by reaction (4). (3), HO2 + NO → NO2 + OH (4). The rate constant k3 was determined to be 1.4 × 1014 exp(?20700 ± 500/RT)s?1. The thermal decomposition lifetimes of HO2O2 at 1 atm total pressure calculated from k3 are 12 s at 298 K, 5 min at 273 K and 1 month at 220 K. Implications of these results for the role of pernitric acid in the lower and upper atmosphere are discussed. 相似文献
A sequential C? H functionalization strategy for the synthesis of the marine alkaloid dictyodendrin B is reported. Our synthesis begins from commercially available 4‐bromoindole and involves six direct functionalizations around the heteroarene core as part of a gram‐scale strategy towards the natural product. 相似文献
A mild, oxidative fluorination approach to a variety of fluorinated phosphorus compounds using trichloroisocyanuric acid (TCICA) and KF was developed as a complement to a recent study on deoxygenative fluorination using oxalyl chloride. Herein, the syntheses of several fluorinated organophosphorus compounds are reported, and both TCICA/KF and oxalyl chloride/KF conditions are compared and contrasted throughout. Initial investigations of the method on other group 15 heteroatoms (i. e., As, Sb, and Bi) are also reported, with varied success. This work notably extends the known TCICA/KF reactivity series to another group of elements beyond previously studied chalcogens (S, Se, and Te) and halogens (iodine) and expands the utility of the previously reported oxalyl chloride/KF method. 相似文献
Measurements, utilizing Rayleigh light scattering, of timeaveraged concentration and unmixedness have been made along the centerlines of axisymmetric turbulent jets formed from six pairs of jet and ambient gases. Jet to ambient density ratios range from 0.14 to 5.11. Findings are compared with predictions of an approx. similarity analysis and with extensive previous literature measurements. It is shown that virtual origins for plots of inverse time-averaged concentration are strongly dependent on global density ratio. Unmixedness values first grow with increasing distance from the jet source and then achieve an asymptote. The flow distance required to reach this asymptote is a strong function of density ratio. 相似文献