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1.
The manganese triacetate oxidation of hindered α 1-positions in a model enone, 3β, 3aβ, 6-trimethyl-3a, 7aβ-dihydro-2(3H), 5(4H)-benzofurandione, provided a procedure for the introduction of the α′-hydroxyenone functionality characteristic of the A ring of certain quassinoids. 相似文献
2.
A simple criterion for estimating the extent of π delocalization in the five-membered ring of pentafulvenes and pentafulvalenes is described. It is based on the fact that changes of bond lengths (induced by exocyclic substituents R 1-R 2 of 1 ) are reflected by systematic changes of 3J(H,H) values, so that linear correlations of σ vs, 3J(H,H)are obtained. Plots of that type ( Fig. 1) are very useful for determining the extent of π delocalization of various pentafulvalenes 2 – 5 ( Fig. 3) which show a very similar behavior to pentafulvenes. In principle, these plots could additionally be used for estimating substituent constants σ or for approximating the extent of π overlap between exocyclic substituents and the π system of pentafulvenes. Charge-density effects of pentafulvenes and pentafulvalenes are observed by substituen-induced shifts of the ring C-atoms ( Fig. 4). 相似文献
3.
A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K
A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm 3 molecule ?1 s ?1: CH 3F, (3.7 ± 0.8) × 10 ?11, CH 3Cl, (3.3 ± 0.7) × 10 ?11; CH 3Br, (3.0 ± 0.7) × 10 ?11; CF 2H 2, (4.3 ± 0.9) × 10 ?12; CO, (5.5 ± 1.0) × 10 ?13 (in 700 torr total pressure of N 2 diluent); CF 3H, (1.4 ± 0.4) × 10 ?13; CF 3CCl 2H (HCFC-123), (1.2 ± 0.4) × 10 ?12; CF 3CFH 2 (HFC-134a), (1.3 ± 0.3) × 10 ?12, CHF 2CHF 2 (HFC-134), (1.0 ± 0.3) × 10 ?12; CF 2ClCH 3 (HCFC-42b), (3.9 ± 0.9) × 10 ?12, CF 2HCH 3 (HFC-152a), (1.7 ± 0.4) × 10 ?11; and CF 3CF 2H (HFC-125), (3.5 ± 0.8) × 10 ?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc. 相似文献
4.
Crystal Structure of Calcium Hydrogenphosphite Monohydrate, Ca(HPO 3H) 2 · H 2O Ca(HPO 3H) 2 · H 2O is triclinic, space group P1 , with a = 7.007(1), b = 8.100(1), c = 6.773(1) Å, α = 84.92(1), β = 95.72(2) and γ = 112.00(1)°; V = 354.1 Å 3, Z = 2; ? x = 2.251 g/cm 3 and ? ob = 2.21(1) g 3/cm 3. The structure was refined to R = 0.019 for 1640 independent reflections. HPO 3H ? ions are linked together by hydrogen bonds (with acid hydrogen atoms) to form parallelograms. Chains of parallelograms are parallel to c axis. The coordination number of the calcium ion is seven; the mean values of Ca? O is 2.409 Å. 相似文献
5.
Organylarsino-substituierte Schwefeldiimide: Die Kristallstrukturanalysen von 3, 7-Di-t-butyl-3H, 7H,-1λ4, 5λ4, 2, 4, 6, 8, 3, 7-dithiatetrazadiarsocin und Bis(diphenylarsino)schwefeldiimid
Organoarsino-Substituted Sulphur Diimides: Crystal Structure Analyses of 3, 7-Di- t-butyl-3H, 7H-1λ 4, 5λ 4, 2, 4, 6, 8, 3, 7-dithiatetrazadiarsocine and Bis (diphenylarsino)sulphur Diimide Reaction of the salt K 2SN 2 with organoarsenic chlorides leads to sulphur diimides containing organoarsino substituents at both ends. Single crystal X-ray structure analyses were carried out for two typical compounds, i.e. the cyclic eight-membered 3, 7-di- t-butyl-3H, 7H-1λ 4, 5λ 4, 2, 4, 6, 8, 3, 7-dithiatetrazadiarsocine ( 1a , prepared from K 2SN 2 and ( t-Bu)AsCl 2 (1:1)) and the open-chain bis(diphenylarsino)sulphur diimide ( 2a , prepared from K 2SN 2 and Ph 2AsCl (1:2)). In both compounds the sulphur diimide groups are coplanar with their directly bound arsenic atoms. This coplanarity principle leads, in the case of 1a , to about conformation (mm2(C 2v) symmetry) of the eight-membered heterocycle; the t-butyl substituents occupy quasi equatorial positions. Small deviations from mm2 symmetry and torsions around the S?N bonds up to 12° can be explained as a consequence of the transnnular repulsion of the lone pairs at the arsenic atoms (As …As distance 3.683(1) Å). In the case of the open-chain S(N? AsPh 2) 2 ( 2a , 2(C 2) symmetry), a cis, cis configuration was found at the S?N double bonds which indicates As…As interaction. The As…As distance (3.379(1) Å) is shorter than in 1a and parallells a reduced interaction of the lone pairs at the As atoms. The S?N bond lenghts (1.517(5) Å in 1 a and 1.521(3) Å in 2a ) are characteristic of sulphur diimides withoug significant π-interaction with the substituents and correspond to S IV?N double bonds. 相似文献
6.
Isotopes of hydrogen (3H, 2H) and oxygen (18O) are perfect candidates for groundwater tracers. A survey of isotopic composition of 34 groundwater samples and one Lake from Vojvodina region (Serbia) is presented here. Tritium activity concentration and stable isotope composition (δ2H, δ18O), as well as deuterium excess, were determined. The groundwater samples lie on the groundwater regression line. Minor deviations and a few lower deuterium excess values indicate waters recharged in a different climate regime and subjected to evaporation, respectively. According to the obtained results, most of the analyzed groundwater can be characterized as modern waters, recharged mostly from precipitation. 相似文献
7.
The 13C, 1H spin-spin coupling constants have been determined for π-benzenechromium tricarbonyl (3) and the π-tropyliumchromium tricarbonyl cation using the 13C{ 2H}double resonance technique described in a previous paper. In addition, conventional analysis of the 1H-coupled 13C NMR spectrum of 3 was carried out and the 1H NMR spectrum of 3 partially oriented in the nematic phase was analysed. Both treatments also allowed the determination of the 1H, 1H coupling constants for this compound. The nJ(CH) results are discussed on the basis of structural data and the theoretical results available. The complexation effects for 1J(CH) are found to correlate with the C? H overlap population and hybridization changes, and those for 3J(CH) with the CC bond lengths and π-bond orders. The dependence of 2J(CH) on CC bond length as well as on the CCH bond angle is indicated. The liquid crystal results are compared with those of related studies. 相似文献
8.
Tritium labelled hexamethyldisiloxane is a suitable material for the internal referencing of 3H NMR spectra. Such a referencing procedure is necessary where the instrument is not capable of scanning 1H resonance under identical experimental conditions. Hexamethyldisiloxane may be tritiated to high activity (typically 1 Ci ml ?1) by Raney nickel catalysed exchange with elemental tritium in a simple one-step procedure. A variety of heterogeneous catalysts are shown to be inactive in the common labelling method involving exchange with tritiated water. 相似文献
9.
Reactions of 6-methylpyrimidine-2,4(1 H,3 H)-dione or 5-hydroxy-6-methyl-pyrimidine-2,4(1 H,3H)-dione with 2-chloromethylthiirane afforded the corresponding substituted 1-(thietan-3-yl)pyrimidine-2,4(1 H,3 H)-diones. The calculations in the framework of approximations PBE/3z, B3LYP/6-31G++(d,p) and MP2/6-31G++(d,p) showed that the alkylation occurred at the atom N 1 of the pyrimidine ring. 相似文献
10.
Information is given on the synthesis of tritium-labeled UDPG by the successive transformation of D-[1- 3H]glucose or D-[6- 3H]glucose by the action of the enzymes hexokinase (EC 2.7.1.1), phosphoglucomutase (EC 2.7.5.1), and UDPG-pyrophosphorylase (EC 2.7.7.9) under conditions ensuring the retention of the tritium label. Methods of obtaining tritium-labelled substrates and intermediate products of their enzymatic transformations in the synthesis of [ 3H]UDPG are discussed.V. G. Khlopin Radium Institute, Leningrad. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 125–128, January–February, 1987. 相似文献
11.
Members of a new class of complexes, 2 (CF 3), 2 (H), 2 (Br), 2 (I), and 2 (OCH 3), have been synthesized in a one-pot method involving the treatment of osmanaphthalynes bearing corresponding substituents ( 1 (CF 3), 1 (H), 1 (Br), 1 (I), and 1 (OCH 3)) with trimethylphosphine (PMe 3) and water. The main reaction process involves two steps, namely a ligand-exchange with trimethylphosphine and nucleophilic addition of water to the Os≡C bond of the osmanaphthalyne. The substituents have a significant influence on the rate of the reaction, as befits a nucleophilic addition. Fortunately, the key intermediate [ 1 (OCH 3)]′ could be successfully captured, and the detailed reaction mechanism has been explored with the aid of density functional theory (DFT) calculations, which were in excellent agreement with the experimental findings. All of the target complexes have been fully characterized by 1H, 31P{ 1H}, and 13C{ 1H} NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. 相似文献
12.
The 1H NMR spectra of 1,6-dicarbomethoxycyclohepta-1,3,5-triene ( 2 ) and 3,4-benzocyclohepta-1,3,5-triene ( 3 ) have been analysed in terms of chemical shifts and coupling constants. A method for the assignment of δ(AA′) and δ(BB′) in AA′BB′ systems, based on the observation of 13C satellites in the 1H NMR spectrum, is described. For J(1,5) in 3 , a negative sign was established. Spin tickling experiments were used to determine the positive sign for J(2,5) in 2 and the negative sign for J(2,7) in 3. The conformation of 3 is discussed. 相似文献
13.
The unprecedented borate hydride Sr 5(BO 3) 3H and deuteride Sr 5( 11BO 3) 3D crystallizing in an apatite-related structure are reported. Despite the presence of hydride anions, the compound decomposes only slowly in air. Doped with Eu 2+, it shows broad-band orange-red emission under violet excitation owing to the 4f 65d–4f 7 transition of Eu 2+. The observed 1H NMR chemical shift is in good agreement with previously reported 1H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1H, 2H, natB, and 11B combined with calculations unambiguously prove the absence of hydroxide ions and the sole incorporation of hydride ions into the borate. The orange-red emission obtained by doping with Eu 2+ shows that the new compound class might be a promising host material for optical applications. 相似文献
14.
Critical energies for 1,3-R sigmatropic migrations (R?H, OH, CH 3 and C 6H 5) have been calculated by means of the MINDO/3 method. This investigation was carried out for the system [RCH 2CH?CH 2] +˙ and the results indicated that hydroxyl group migration is energetically favoured (critical energy = 53 kJ mol ?1). Calculations are also presented for [3-buten-2-ol] +˙ isomerizations. The lowest energy pathway is related to the [2-buten-1-ol] +˙; the corresponding critical energy for OH migration is equal to 33 kJ mol ?1 in this case. 相似文献
15.
The production and reactions of vinyl radicals and hydrogen atoms from the photolysis of vinyl iodide (C 2H 3I) at 193 nm have been examined employing laser photolysis coupled to kinetic-absorption spectroscopic and gas chromatographic product analysis techniques. The time history of vinyl radicals in the presence of hydrogen atoms was monitored using the 1,3-butadiene (the vinyl radical combination product) absorption at 210 nm. By employing kinetic modeling procedures a rate constant of 1.8 × 10 ?10 cm 2 molecule ?1 s ?1 for the reaction C 2H 3 + H has been determined at 298 K and 27 KPa (200 torr) pressure. A detailed error analysis for determination of the C 2H 3 + H reaction rate constant, the initial C 2H 3 and H concentrations are performed. A combined uncertainty of ±0.43 × 10 ?10 cm 2 molecule ?1 s ?1 for the above measured rate constant has been evaluated by combining the contribution of the random errors and the systematic errors (biases) due to uncertainties of each known parameter used in the modeling. © 1995 John Wiley & Sons, Inc. 相似文献
16.
A kinetic study of the reactions of H atoms with CH 3SH and C 2H 5SH has been carried out at 298 K by the discharge flow technique with EPR and mass spectrometric analysis of the species. The pressure was 1 torr. It was found: k1 = (2.20 ± 0.20) × 10 ?12 for the reaction H + CH 3SH (1) and k2 = (2.40 ± 0.16) × 10 ?12 for the reaction H + C 2H 5SH (2). Units are cm 3 molecule ?1 s ?1. A mass spectrometric analysis of the reaction products and a computer simulation of the reacting systems have shown that reaction (1) proceeds through two mechanisms leading to the formation of CH 3S + H 2 (1a) and CH 3 + H 2S (1b). 相似文献
17.
(NH 4) 2PO 3H, H 2O crystallizes in the monoclinic system, space group P2 1/c, with a = 6.322(1) Å, b = 8.323(1) Å, c = 12.676(1) Å, β = 98.84(1) and Z = 4. The structure was refined to R = 0.022 based on 853 independent X-Rays intensities. Improved dimensions of the tetrahedral PO 3H 2? ion have been obtained: P?H = 1.34(2) and P?O = 1.514(2) Å. The geometry of this ion is compared with that of PO 3F 2? and SO 32? ions and we find a decrease of the volume: V F? > V H+ > V lone pair. 相似文献
18.
Synthesis, Crystal Structure, and Solid State MAS-NMR Spectroscopic Investigation of K 5H(CN 2) 3 Single phase K 5H(CN 2) 3 was synthesized by reaction of KHCN 2 with metallic potassium in liquid ammonia or by reaction of KNH 2 with melamine C 3N 3(NH 2) 3 at 320 °C, respectively. The crystal structure was determined from X-ray powder and single crystal data: K 5H(CN) 3, space group Im3m, a = 795.68(7) pm, Z = 2, R1 = 0.025, wR2 = 0.0438. In the solid K 5H(CN 2) 3 contains K + and CN 22–, the anions exhibit D ∞h symmetry. According to 1H and 13C solid state MAS-NMR investigations, temperature dependent impedance spectroscopy, and FTIR spectroscopy the protons are only loosely bound to the CN 22– ions. The proton conductivity shows a sharp increase above 70 °C. 相似文献
19.
The reactions of 9-methyl-, 9-ethyl- and 9-propyl-anthracene with CF 3CO 2[ 2H] in C[ 2H]Cl 3 and with FSO 3[ 2H] in SO 2ClF have been investigated. Using 4 equivalents of CF 3CO 2[ 2H] at 50° 1H- 2H exchange was observed only for the 10-H and the side-chain α-hydrogens, and on using 8 and 12 equivalents at 50° also for the aromatic α-hydrogens. Treatment of the substrates with FSO 3[ 2H] at -60° leads to the stable 9-alkyl-[10- 2H]-10-anthracenium ions. On warming up to ?25° a slow 1H- 2H exchange of only the 10- 1H of these anthracenium ions is observed. A mechanism for the 1H- 2H exchange of the aromatic and the side-chain α-hydrogens of the 9-alkylanthracenes is presented. 相似文献
20.
The complexes [(ν 3-RC 3H 4)Pd{R 1NS(R 2)NR 1}] (R H, CH 3;R 1 aryl; R 2 CH 3, t-C 4H 9) have been obtained from the reaction of [(ν 3-RC 3H 4)PdCl] 2 with [Li{R 1NS(R 2)NR 1}]; two isomers are produced, differing in the orientation of the allyl group. The sulfurdiimino group has some π-allylic character. The compounds decompose in solution into azo—arenes and [(ν 3-RC 3H 4)Pd(SR 2)] 2, and this is shown to be dependent upon steric and electronic factors.The properties of the sulfurdiimino compounds are compared with those of the compounds [(ν 3-RC 3H 4)Pd(R 3N 3R 3)] 2 and [(ν 3-RC 3H 4)Pd(R 3NC(R 4)NR 3)] 2 (R H, CH 3;R 3 CH 3, aryl; R 4 H, CH 3), which have been prepared by new methods. 相似文献
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