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1.
For a series of substituted arylsulfenyl chlorides the stereochemistry of AdE-reactions with a series of substituted Z- and E-β-deuterostyrenes has been elucidated. Non-stereospecific reaction was observed only for the pair 2,4-dinitrobenzenesulfenyl chloride-p-methoxystyrene; for all the other reactants the reaction proceeded in a strictly stereospecific manner. 相似文献
2.
3.
Conclusions The decomposition of the complex obtained in the reaction of pivaloyl tetrafluoroborate with norcarane and its 1-methyl and 1-phenyl derivatives by water gives 1-hydroxy-3-pivaloyl derivatives of cyclohexanes and the corresponding unsaturated ketones. The hydride decomposition of the same complex leads to derivatives of 6-oxabicyclo[3.2.1]octane.For preliminary report see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2512–2518, November, 1976. 相似文献
4.
1. | From MNDO quantum chemical calculations, opening of the episulfonium ion ring by neutral nucleophiles X (X=NH3 and HCN) and related SN2 reactions of protonated methylthiol (PMT) with X proceed through formation of pre-reaction complexes in which X is coordinated either at the reacting C atom or (only in opening of episulfonium ion rings) at the center of the C-C bond. |
2. | In their electronic structure, the transition states for the reactions are reminiscent of a carbocation simultaneously reacting with the attacking and the leaving nucleophilic fragments (X S). |
3. | Opening of episulfonium ion rings proceeds slightly more easily (Ea 10–12 kcal/mole) than substitution in PMT (Ea 22–25 kcal/mole). The ease of ring opening for episulfonium ions is due to the large exothermicity of the reaction and the lower internal activation barrier compared with SN2 reactions in PMT. |
5.
A two-step synthesis was proposed for the tetracyclic triquinane bis-enone from two monocyclic precursors. The bis-enone obtained is a structural fragment of retigeranic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1908–1910, August, 1990. 相似文献
6.
The -arylthioalkylation of 2-methoxy-1,3-butadiene is regiospecific at the alkoxy-substituted C=C bond, giving 6-arylthioalk-1-en-3-ones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2036–2040, September, 1990. 相似文献
7.
On reaction of 1,2:5,6-di-O-isopropylidenc-3-O-(p-tolylsulfonyl)-α-D-glueofuranose ( 1 ) with hydrazine hydrate at 140° besides formation of 3-deoxy-3-hydrazino-1,2:5,6-di-O-isopropylidene-α-D-allofuranose ( 2 ) and 3-dcoxy-1,2:5,6-di-O-isopropylidene-α-D-erythro-hex-3-enofuranose ( 3 ), ring transformation into 3-[4′-(2′,2′-dimethyl-1′,3′-dioxolanyl)]pyridazine ( 4 ) takes place. At 170°, however, only 2 and 4 are formed, indicating that 3 is the precursor of 4. Treatment of 3 with hydrazine hydrate at 170° indeed gives a nearly quantitative ring expansion into 4. Treatment of 3-dcoxy-3-hydrazino-1,2:5,6-di-O-isopropylidenc-α-D-glucofuranose ( 8 ) as well as the stereoisomeric allofuranose 2 with concentrated hydrochloric acid gives a nearly quantitative ring interconversion into 3-(D-erythro-trihydroxypropyl)pyrazole ( 9 ). 相似文献
8.
Summary Three aspects with respect to the selection of solvents for static coating of capillary columns, i.e. coating speed, occurrence of bumping and solubility of stationary phases are discussed. Hypotheses are proposed in an attempt to explain the observed facts that mixed solvents result in much higher coating speeds than those obtained from pure solvents, that a proper choice of solvents together with a good and uniform deactivitation of the column inner wall is needed to prevent bumping. Stationary phase solubility vs. solvent composition is also briefly discussed. 相似文献
9.
B. Buchholz B. Kühnreich H. G. J. Smit V. Ebert 《Applied physics. B, Lasers and optics》2013,110(2):249-262
Accuracy, precision, repeatability and long-term stability, are the most important requirements to enable reliable airborne humidity measurements, which are needed for climate models or to validate e.g. remote sensing instrumentation like satellites. However, various hygrometer artifacts which depend on the individual sensor principle and the application profile frequently cause problems and significantly complicate the hygrometer choice. Sensor intercomparisons are one way of providing the information for an optimal choice. In this paper we present the first part of a blind, static, laboratory-based intercomparison of a new, calibration-free, 1.4 μm diode laser-based, optical hygrometer (SEALDH) with the two most important measurement principles for airborne hygrometry (frost-point hygrometers, FPH, and Lyman-alpha fluorescence hygrometers, LAFH). During three days of measurement, the TDL-hygrometer achieved a H2O resolution of up to 0.5 ppmv (Δt=2 sec) at tropospheric pressure and H2O concentration levels (100–800 hPa, 10 to 8000 ppmv H2O). Its absolute accuracy was investigated via blind intercomparison with two reference FPHs and a LAFH. Without any calibration of SEALDH, i.e. without a comparison to a water vapor standard, we achieve an excellent agreement with the reference sensors, with an average systematic offset (over all three days) of ?3.9 %±1.5 %, which is fully consistent with the sensor’s uncertainty bounds. Further we also reevaluated the SEALDH data of day 2 and 3 in a calibrated mode using an independent set of FPH data from the first day and found an 8-fold accuracy improvement, yielding an excellent overall relative deviation of only 0.52 %±1.5 % with respect to a LAFH and a D/FH sensor. 相似文献
10.
Erwin A. J. M. Bente Yohan Barbarin Martijn J. R. Heck Meint K. Smit 《Optical and Quantum Electronics》2008,40(2-4):131-148
In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking. 相似文献