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1.
Pronounced solvent dependence is observed in the infrared and electronic spectra of the new η-allyl complexes (η-R′ C3 H4)M(CO)2 L2X (M = Mo or W; R′ = H or Me; X = Ct, By, I or NCS; L2 = 1,2-ethanediylidenediimines or 2-pyridinaldimines). 相似文献
2.
Ethylisobutrazine hydrochloride is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V). It forms a red-colored species with vanadium(V) in 3.5–6.5 M phosphoric acid medium. An eight-fold molar excess of reagent is necessary for the full development of the color. The red species exhibits an absorption maximum at 518 nm with a molar absorptivity of 9.75 × 103 liters mol−1 cm−1. Sandell's sensitivity is 5.2 ng cm−2. Beer's law is obeyed over the range 0.1–6.2 ppm of vanadium(V) with an optimum concentration range of 0.4–6.0 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions, are reported. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels that contain chromium, molybdenum, manganese, nickel, copper, tungsten, and titanium. 相似文献
3.
Olofson's group and Norris and Henry have reported proton exchange rates for a variety of azolium cations in aqueous solution. They found that ring protons in positions located α- to pyrrole-type N atoms exchange much faster than those located β- to such nitrogens, and that addition of pyridine-type nitrogen to the ring also caused a large increase in rate of exchange. This report describes the results of CNDO/2 calculations on azolium cations representative of those studied experimentally, and on the zwitterions resulting from the deprotonation of these cations. The calculated vapor-phase energies of deprotonation are in agreement with the structure-reactivity trends summarized above, but the calculated effect of added nitrogen is unexpectedly small relative to the effect of interchanging α- and β- pyrrole-type N atoms. The calculated charge distributions and one- and two-atom contributions to the calculated energies of deprotonation are analyzed in terms of classical organic mechanisms for transmission of substituent effects. The results of this analysis suggest that the relative reactivities of isomeric tetrazolium cations are determined primarily by coulombic effects, but that relative reactivities of isomeric positions in the imidazolium and pyrazolium series are apparently determined primarily by inductive and hybridization effects. π-Electron resonance (contributions from carbenoid resonance forms) is apparently not of overriding importance. When nitrogen is added to the ring in an α-position relative to the CH group undergoing exchange, the resulting increase in CH acidity seems to be due to inductive and hybridization effects, partially offset by a coulombic effect due to the negative charge on the added nitrogen. If classical σ-inductive and hybridization effects from an added β-nitrogen are at all influential, they seem much less so than from an added α-nitrogen; thus according to CNDO/2 these effects alone apparently cannot explain the observed large rate increase due to added β-nitrogen. The possible importance of solvent effects, delocalization of the added negative charge into the σ-framework and coulombic effects due to the added nitrogen are discussed. 相似文献
4.
Vincent L. Vilker Clark K. Colton Kenneth A. Smith Donald L. Green 《Journal of membrane science》1984,20(1):63-77
Side-by-side measurements were made of osmotic pressure and ultrafiltration flux from a stirred cell for separate saline solutions of the proteins, bovine serum albumin, bovine fibrinogen, human low density lipoprotein and for polyethylene oxide .in distilled water. Albumin osmotic pressures were large enough to conclude that concentration polarization limits ultrafiltrate flux mostly by decreasing the driving forceΔP -Δπ. For the other large macrosolutes, concentrated-solution osmotic pressures were so small that polarization probably limits flux at the usual levels of applied pressure by adding a hydrodynamic resistance (gel layer) in series with the membrane resistance. 相似文献
5.
The reactions of Fe(CO)5, Fe(CO)4P(C6H5)3, M(CO)6 (M W, Mo, Cr), and (CH3C5H4Mn(CO)3 with KH and several boron and aluminium hydrides were investigated. Iron pentacarbonyl was converted quantitatively to K+Fe(CO)4-(CHO) by hydride transfer from KBH(OCH3)3 allowing isolation of [P(C6H5)3]2-Nn+Fe(CO)4(CHO)? in 50% yield. Lower yields were obtained with LiBH(C2H5)3, and other hydride sources gave little or no formyl product. The stability of Fe(CO)4(CHO)? in THP was found to depend on the cation, decreasing in the order [P(C6H5)3]2N+ > K+ > Na+ > Li+. No formyl complexes were isolated and no spectroscopic evidence for formyl formation was observed in the reactions of the other transition metal carbonyls with several hydride sources. Fe(CO)4-P(C6H5)3 gave K2Fe(CO)4 when treated with KHB(OCH3)3. When treated with LiBH(C2H5)3, W(CO)6 gave a mixture of HW2(CO)10?and (OC)5W(COC2H5)?; the latter was methylated to give the carbene complex (OC)5WC(OCH3)C2H5. 相似文献
6.
Reduction of ferrocenylketoximes by titanium trichloride provides a convenient route for the preparation of ferrocenyliminium salts, which have been shown to be useful for the synthesis of new derivatives. 相似文献
7.
Waldemar Adam Günter Klug Dieter Scheutzow Karl Peters Eva-Maria Peters Hans-Georg von Schnering 《Tetrahedron letters》1982,23(28):2837-2840
The endoperoxides and , respectively 9-methoxy- and 1-methoxy-7,8-dioxabicyclo[4.2.2]deca-2,4,7-trienes, and the urazoles and , respectively 9-methoxy- and 2-methoxy-7,8-diazantricyclo[4.2.2]deca-2,4,9-trien--methyl-7,8-dicarboximide, were obtained in the cycloaddition of singlet oxygen and -methyl-1,2,4-triazoline-3,5-dione (MTAD) to methoxycyclooctatetraene (MCOT). 相似文献
8.
Therapeutic systems can provide pre-programmed, unattended delivery of a drug at a rate, and for a time period, established to meet a specific therapeutic need. The system can be designed to minimize the patient's intervention and to optimize compliance with the prescribed regimen. The ocular therapeutic system described here for the control of intraocular pressure in glaucoma delivers pilocarpine at 20 or 40 μg/h for one week, and fits comfortably into the cul-de-sac of the eye. The intrauterine progesterone contraceptive system described here represents a new approach to steroidal contraception that localizes the effect of the hormone progesterone to the uterus, delivering the hormone at a rate of 65 μg/day for one year. Both of these systems are designed to deliver drug into their immediate locale, and are thus topical dosage forms. The transdermal therapeutic system described here has been designed to deliver scopolamine across intact skin and into systemic blood to achieve an antinausea effect. The pharmacokinetics of scopolamine are such that, to minimize the time required for the onset of drug action, drug should be presented at an initially high rate, i.e. as a priming dose, to attain the therapeutically effective drug level, and then at a constant rate, so as to maintain the therapeutically effective level. This system functions according to the priming dose/maintenance rate design requirement. 相似文献
9.
William G. Lyon Darrell W. Osborne Howard E. Flotow 《The Journal of chemical thermodynamics》1975,7(12):1189-1194
The heat capacity of a sample of Cs2CrO4 was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure Cpo(298.15 K), the entropy So(298.15 K), the enthalpy {Ho(298.15 K) - Ho(0)} and the function were found to be (146.06 ± 0.15) J K?1 mol?1, (228.59 ± 0.23) J K?1 mol?1, (30161 ± 30) J mol?1, and (127.43 ± 0.13) J K?1 mol?1, respectively. The heat capacity Cpo(298.15 K) and entropy So(298.15 K) and entropy So(298.15 K) of Rb2CrO4 are estimated to be (146.0 ± 1.0) J K?1 mol?1 and (217.6 ± 3.0) J K?1 mol?1, respectively. 相似文献
10.
We measured the temperature dependence of the Debye-Waller factor for the phosphorescence of a special naphthalene X trap and performed a lineshape calculation of the phonon sideband based on a Morse oscillator. The experimental, as well as the theoretical, results agree with the assumption of a pseudo-localized mode. 相似文献
11.
The effects of calcination temperature on the development of pore size and on the SO2 sorption capacity have been investigated. It has been shown that the optimal temperature of sulfur retention observed in a fluidized-bed combustor can very possibly be due to pore size variations because of calcinations at different temperatures. 相似文献
12.
New dienamino esters (3b–k) were obtained by addition of enamino esters (1b–g) to methyl and ethyl propiolate (2a–b). Z,E-Configuration and a transoid conformation were assigned on the basis of spectral data which indicate also noncoplanarity of phenyl groups whenever present. The corresponding adducts with acetylenedicarboxylic ester (18 and 19) have a cisoid conformation and it was possible to differentiate between thermodynamically and kinetically controlled products. Deuteration experiments showed the existence of a 1,5-proton transfer while comparative examination of a whole series of NMR spectra furnished evidence for a head to tail attachment. Attempts to trap the intermediate zwitterion 10 resulted in the formation of 15a–b corresponding to a cyclobutene intermediate. The reaction repiesents a new synthesis of the benzene nucleus and a practical method to obtain the methyltrimesic and 2,4,6-biphenyltricarboxylic acids. Additions of enamino esters to the triple bond are best interpreted as occurring through a common key intermediate, a zwitterion of type 5 or 10. The former collapses by proton transfer and the resulting imino-derivative 6 tautomerizes to 3. The latter cyclizes to a non-isolable cyclo-butene 12 which by opening of the ring produces the dipolar species 13 which further reacts with propiolic ester. By cyclization of the dienamino esters 3a–j but not of 18 and 19 in dipolar aprotic solvents at 160–190° the corresponding a-pyridones 4a–t were obtained in good yields. 相似文献
13.
The crystal structure of tricarbonyl[1,2,2a,12a-η-5,10-dimethyldibenzo[a,c] cyclobuta[f] cyclooctene-3,12-dione] iron, C20O2H14Fe(CO)3, has been determined by the single crystal X-ray diffraction technique using data collected with a fully automated diffractometer. The unit cell is monoclinic, space group P21/c with a = 12.025(2), b = 23.204(3), c = 14.614(2) Å, β = 102.16(2)°, and contains eight molecules (two per asymmetric unit). The structure was elucidated to study the coordination of the iron atom and to correlate the conformation of the eight-membered ring with an NMR study. The final structure was obtained by Patterson-superposition and Fourier techniques and refined by full-matrix least-squares to a crystallographic residual of 0.070. In both independent molecules the iron atom is 1.77 Å from the cyclobutadiene ring to which it is coordinated. The eight-membered ring is flattened from a boat conformation and the six-membered rings are twisted from coplanarity by an angle of 74°. The twist is such that if one ring points above the eight-membered ring, the other ring will point below it with concomitant pointing in the opposite sense by neighboring carbonyl groups. Such a structure has conformational chirality. It is postulated that the stability of each enantiometer is due to the particularly high energy of the transition state through which each would pass to achieve inter-conversion. 相似文献
14.
Kenneth N. Marsh Warren A. Allan Alan E. Richards 《The Journal of chemical thermodynamics》1984,16(12):1107-1120
Excess molar enthalpies HmE and excess molar volumes VmE have been measured for xC3H7NO2 + (1 ? x)c-C6H12 at 298.15 and 318.15 K; +(1 ? x)CCl4 at 298.15 and 318.15 K; +(1 ? x)C6H6 at 298.15 and 318.15 K; +(1 ? x)C6H14 (VmE only) at 298.15 K; +(1 ? x)p-C6H4(CH3)2 at 298.15 K; and for xCH3CH(NO2)CH3 + (1 ? x)c-C6H12 at 298.15 and 318.15 K; +(1 ? x)CCl4 at 298.15 and 318.15 K; +(1 ? x)C6H6 at 298.15 K; +(1 ? x)C6H14 at 298.15 K; +(1 ? x)(CH3)2CHCH(CH3)2 for HmE at 318.15 K and for VmE at 298.15 K; and +(1 ? x)C16H34 at 298.15 K. The HmE′s were determined with an isothermal dilution calorimeter and the VmE′s with a continuous-dilution dilatometer. Particular attention was paid to the region dilute in nitroalkane. In general HmE is large and positive for (a nitropropane + an alkane), less positive for (a nitropropane + tetrachloromethane), and small for (a nitropropane + benzene) and for (a nitropropane + 1,4-dimethylbenzene). The mixture with hexadecane shows phase separation. VmE is large and positive for (1-nitropropane + cyclohexane), less positive for (1-nitropropane + hexane), and S-shaped for (1-nitropropane + tetrachloromethane) with negative values in the 1-nitropropane-rich region. For (1-nitropropane + benzene) and for (1-nitropropane + 1,4-dimethylbenzene) VmE is negative. For mixtures with 2-nitropropane the results are similar except that for benzene VmE is S-shaped with positive values in the 2-nitropropane-rich region. 相似文献
15.
Semi-empirical computations on the C11H11 cation reported by Goldstein and Kline indicate that a classical structure suggested by models is not an appropriate representation of the system. A system with Cs symmetry differing in detail from the “quasi D2d” form proposed by the discoverers is found to be the stable form. The reasons for easy rearrangement in this system are discussed. 相似文献
16.
Elimination reactions on isomeric mixtures of and 1,2-dihalo-2,3,3-trifluorocyclobutanes are reported. In zinc-promoted dehalogenations a steady decrease in the relative amount of the isomers compared to the isomers occured, with 2,3,3-trifluorocyclobutene as the sole product. The isomers reacted at a faster rate in potassium hydroxide induced eliminations to yield a slight predominance of 1-halo-2,3,3-trifluorocyclobutenes over 3-halo-3,4,4-trifluorocyclobutenes. However, with triethylamine as the inducing base, an increased rate of elimination from the isomers was noted along with almost exclusive formation of 3-halo-3,4,4-trifluorocyclobutenes. 相似文献
17.
Conditional stability constants, enthalpies and entropies of complexation at pH 7.5 and ionic strength 0.1 have been determined for neptunium(V) complexes of phosphate, salicylate, phthalate and citrate. Phosphate forms a complex with log β = 2.36 ± 0.42 at 25°C, ΔH°c = ? 69.9 kJ/mole and ΔS°c = ? 188 J/mole-K. At pH 7.5 salicylate does not form a complex with neptunium(V) due to the low charge density of the NpO2+ ion and incomplete ionization of the salicylate ion. Phthalate forms a complex with log β = 3.43 ± 0.33 at 25°C, ΔH°c = 33.5 kJ/mole and ΔS°c = 182 J/mole-K. Citrate forms a complex with log β = 4.84 ± 0.72 at 25°C, ΔH°c = 14.0 kJ/mole and ΔS°c = 140 J/mole-K. In all cases, only 1:1 complexes were identified. 相似文献
18.
Two parallel sets of CNDO/2 calculations have been carried out for 1H-5-aminotetrazole (1), 2-methyl-5-aminotetrazole (2), 1,3-dimethyl-5-aminotetrazolium cation (3) and the tetrazolate anion (4). In one set, the molecular geometry was represented by a regular pentagon 1·33 Å on a side, and in the other the experimentally determined molecular geometries were used. The calculated electronic structures from the two sets of calculations are compared; both sets predict similar trends in variation of atomic charges and bond indices with structure. Where comparison is possible, these trends seem to be generally in agreement with expectations based on classical concepts such as resonance. It is noted that the relative magnitudes of σ-electron bond indices seem to parallel those of the π-electron bond indices in many cases, although the σ-bond indices show much smaller variation in absolute magnitude as compared with the π-bond indices. A brief discussion of the relative merits of various geometrical models is presented; it is suggested that, in order to combine the advantages of both approaches, standard and experimentally-determined geometries should be used side-by-side whenever possible. A procedure for speeding convergence by use of a damping factor is described. 相似文献
19.