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1.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
2.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
3.
The macrocyclic compound, [1,2-C 2B 10H 10-1,4-C 6H 4-1,7-C 2B 10H 10-1,4-C 6H 4] 2 (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)- ortho-carborane. The X-ray crystal structure of 5·C 6H 6·6C 6H 12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol −1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful. 相似文献
4.
Studies on the decomposition rates of the Mn(III) complex of cyclohexanediaminetetra-acetate (DCTA) in light and in darkness have shown that this complex is more stable than the one derived from ethylenediaminetetra-acetate. The optimum pH range for the determination of dissolved oxygen by means of the Mn(III)-DCTA complex is found to be between 3 and 4. The absorbance of this complex is independent of the amount of DCTA used (in the range 0.2–1.0 g) with water samples containing a maximum of 3.2 ppm of dissolved oxygen. Significant interferences are caused by the presence of CO 2−3, HCO −3, S 2O 2−3, PO 3−4, I −, NO −2, SO 2−3, Ca 2+, Fe 2+ and Fe 3+ at 500 times the oxygen concentration. 相似文献
5.
We have recorded the infrared absorption spectrum of pyrrole at 0.005 cm −1 spectral resolution using a Fourier transform interferometer. The rotational analysis of the fundamental N---H stretch (1 10) at 3530.811343(82) cm −1 was performed. A set of 13 upper state rovibrational parameters was determined, allowing the 2715 assigned rovibrational lines to be reproduced with a standard deviation of 1.3 10 −3 cm −1. An attempt to record the fundamental band under slit-jet conditions is reported. The role of hot bands accompanying the series of the N---H stretch excitation is investigated. Effective vibrational parameters — ω 01, X011, Y111, X1,24 — are obtained. The lower level in the hot band series is unambiguously identified as the V24 = 1 level, by retrieving X1,24 independently, from other spectral data. The observation of the complex band pattern accompanying the N---H series in the higher overtone range is discussed with the help of new data, recorded around the 1 50 band at different temperatures using intracavity laser optoacoustic spectroscopy. 相似文献
6.
The rate coefficients of the reactions: (1) CN + H 2CO → products and (2) NCO + H 2CO → products in the temperature range 294–769 K have been determined by means of the laser photolysis-laser induced fluorescence technique. Our measurements show that reaction (1) is rapid: k1(294 K) = (1.64 ± 0.25) x 10 −11 cm 3 molecule −1 s −1; the Arrhenius relation was determined as k1 = (6.7 ± 1.0) x 10 −11 exp[(−412 ± 20)/T] cm 3 molecule −1 s −1. Reaction (2) is approximately a tenth as rapid as reaction (1) and the temperature dependence of k2 does not conform to the Arrhenius form: k2 = 4.62 x 10 −17T1.71 exp(198/ T) cm 3 molecule −1 s −1. Our values are in reasonable agreement with the only reported measurement of k1; the rate coefficients for reaction (2) have not been previously reported. 相似文献
7.
X-Ray crystallographic studies on [NEt 4] 2[Cr 2[(O 2CC 2H 5) 4(NCS) 2] show that the Cr–Cr separation (2.467Å) in the dinuclear anion is one of the longest known. The thiocyanato groups are N-bonded, and the results emphasize the known sensitivity of the quadruple Cr–Cr bond to the nature of the axial ligands. The compound crystallises in the tetragonal space group P4/ mnc with two molecules per unit cell, the dimensions of which are a = b = 9.785(1), c = 21.186(2) Å. Magnetic investigations from room to liquid nitrogen temperature on the tetra-μ-propionato complex and on [NMe 4] 2 [Cr 2(O 2CCH 3) 4(NCS) 2] show that both complexes have been obtained free from paramagnetic chromium(III) impurities. Their weak paramagnetic susceptibilities ( Xcr is approx. 200 x 10 −6 cm 3 mol −1 at 295 K and 50 x 10 −6cm 3mol −1 at 90 K) are inherent, and are ascribed to temperature independent paramagnetism at low temperature plus para-magnetism arising from slight population of the triplet state (2 J 700 cm −1, g = 2, N = 50 x 10 −6cm 3mol −1) at higher temperatures. 相似文献
8.
The rate constants, k1 and k2 for the reactions of C 2F 5OC(O)H and n-C 3F 7OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k1 and k2 were determined as (9.24 ± 1.33) × 10 −13 exp[−(1230 ± 40)/ T] and (1.41 ± 0.26) × 10 −12 exp[−(1260 ± 50)/ T] cm 3 molecule −1 s −1. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k1 and k2. The atmospheric lifetimes of C 2F 5OC(O)H and n-C 3F 7OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively. 相似文献
9.
Tert-butyl chloride has been broadly studied experimentally through various techniques such as X-ray crystallography, DTA, and NMR. It was also studied experimentally through nuclear quadrupole resonance (NQR), but this study was limited and incomplete. In this paper, we present a more detailed study of TBC through the NQR of 35Cl. Our results show that near 120 K, the onset of the CH 3 groups semirotations around symmetry axis C3 takes place with an activation energy U=16.1 kJ mol −1. This intramolecular movement produces a T1 minimum near 148 K and is the dominant mechanism of the nuclear spin-lattice relaxation in phase III of this compound. In phase II of TBC, we show that there are not only methyl groups semirotations, but also semirotations of the whole molecule around a different axis from the symmetry axis C′ 3 (C–Cl bond) with an activation energy of E=10.4 kJ mol −1. 相似文献
10.
The structure of 1-chloronaphthalene, C 10H 7–Cl, at 293 K was investigated using the X-ray diffraction method. Monochromatic radiation MoK ( λ=0.71069 Å) enabled the determination of the scattered radiation intensity between S0=4πsin 0/λ=0.430 Å −1 and Smax=14.311 Å −1. The interpretation of the results was carried out using the reduction method of Blum and Narten. Experimental distributions of X-ray scattered intensity were compared with theoretical results predicted for a proposed model of 1-chloronaphthalene molecule. The electron-density radial-distribution function
was calculated and some intra- and intermolecular distances in liquid 1-chloronaphthalene were determined. X-ray structural analysis was applied to determine the packing coefficient of 1-chloronaphthalene molecules. 相似文献
11.
Recent results (post-1990) on the synthesis and structures of bis(trimethylsilyl)methyls M(CHR 2) m (R = SiMe 3) of metals and metalloids M are described, including those of the crystalline lipophilic [Na(μ-CHR 2)] ∞, [Rb(μ-CHR 2)(PMDETA)] 2, K 4(CHR 2) 4(PMDETA) 2, [Mg(CHR 2)(μ-CHR 2)] ∞, P(CHR 2) 2 (gaseous) and P 2(CHR 2) 4, [Yb(CHR 2) 2(OEt 2) 2] and [{Yb(CR 3)(μ-OEt)(OEt 2)} 2]; earlier information on other M(CHR 2) m complexes and some of their adducts is tabulated. Treatment of M(CHR 2) (M = Li or K) with four different nitriles gave the X-ray-characterized azaallyls or β-diketinimates
,
and
(LL′ = N(R)C( tBu)CHR, L′L′ = N(R)C(Ph)C(H)C(Ph)NR, LL″ = N(R)C(Ph)NC(H)C(Ph)CHR, R = SiMe 3 and Ar = C 6H 3Me 2-2,5). The two lithium reagents were convenient sources of other metal azaallyls or β-diketinimates, including those of K, Co(II), Zr(IV), Sn(IV), Yb(II), Hf(IV) and U(VI)/U(III). Complexes having one or more of the bulky ligands [LL′] −, [L′L′] −, [LL] −, [LL″] −, [L″L] −, [LL] − and [{N(R)C( tBu)CH} 2C 6H 4-2] 2− are described and characterized (LL = N(H)C(Ph)C(H)C(Ph)NH, L″L = N(R)C( tBu)C(H)C(Ph)NR, LL = N(R)C( tBu)CHPh). Among the features of interest are (i) the contrasting tetrahedral or square-planar geometry for
and
, respectively, and (ii) olefin-polymerization catalytic activity of some of the zirconium(IV) chlorides. 相似文献
12.
Geometry optimizations at the UHF/6-31G * and UMP2/6-31G * levels of theory were performed to find the transition state in the interconversion between norbornadiene (N) and quadricyclane (Q) radical cations. Two transition structures, TS +·1 and TS +·2, were obtained which have C1 and C2 symmetry, respectively. Vibrational analysis at the UHF and UMP2 levels of theory and IRC calculation showed that TS +·1 is the true transition state connecting N +· and Q +·, while TS +·2 is a second order saddle point. 相似文献
13.
The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO 4 single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C2h factor group is observed. The vibrational factor group appears to be C2. This implies C1 site symmetry for the SO 2−4 ions. The polarization features of the HSO −4 ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO 3 group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance. 相似文献
14.
Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms with iodobenzene (C 6H 5I) in 20–700 Torr of N 2, air, or O 2 diluent at 296 K. The reaction proceeds with a rate constant k(Cl+C 6H 5I)=(3.3±0.7)×10 −11 cm 3 molecule −1 s −1 to give chlorobenzene (C 6H 5Cl) in a yield which is indistinguishable from 100%. The title reaction proceeds via a displacement mechanism (probably addition followed by elimination). 相似文献
15.
Vitamin A,dissolved in liquid paraffin, is stable below room temperature, but suffers oxidative decomposition at 80°, giving its epoxide as the main product. The rate of decomposition of vitamin A (V A) at 80° in the presence of oxygen (partial pressure of p) and a small amount of cobaltous stearate (Co) is expressed as: d[V A]/d t = 3·15 × 10 −1:[V A][Co] p1·48 + 1·51 × 10 −5[V A] p0·33 + 0·33 × 10 −5[V A], where the last term represents the spontaneous thermal decomposition. 相似文献
16.
The reaction: F + HCl→ HF ( v 3) + Cl (1), has been initiated by photolysing F 2 using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k1 = (7.0 ± 0.5) × 10 −12 cm 3 molecule −1 s −1, and for the relaxation of HF( v = 3) by HCl, CO 2, N 2O, CO, N 2 and O 2: kHCl = (1.18 ±0.14) × 10 −11 kCO2 = (1.04 ± 0. 13) × 10 −12, kN2O = (1.41 ± 0.13) × 10 −11 kCO = (2.9 ± 0.3) × (10 −12, kN2 = (7.1 ± 0.6) × 10 −14 and kO2 = (1.9 ± 0.6) × 10 −14 cm 3molecule −1s −1. 相似文献
17.
The structures of two glycinohydroxamoto (GHA) complexes of Ni(II) and Co(III) have been determined by single-crystal X-ray diffraction methods. The crystals of Ni(GHA) 2 are monoclinic with a = 5.360(1), b = 7.315(4), c = 10.194(4) Å, β = 96.57(3), Z = 2, and space group P2 1/ c. The crystals of Co(GHA) 3•1/2 H 2O are monoclinic with a = 22.467(19), b = 8.041(4), c = 13.700(11) Å, β = 116.01(7), Z = 8, and space group C2/ c. The values of the final residuals R for Ni(GHA) 2 and Co(GHA) 3•1/2 H 2O are 0.0275 and 0.032, respectvely. The molecular structures of Ni(GHA) 2 and Co(GHA) 3 consist of a square planar and an octahedral coordination, respectively, with the glycinohydroxamato (NH 2CH 2CONOH −) ligands coordinating to the metal ion via the N (amino) and the N (NOH −). These two complexes are the first well-established cases of coordination of the NHO − group of a hydroxamic acid to a transition metal via the nitrogen atom. 相似文献
18.
The gas-phase stabilities of cluster ions SF +m (SF 6) n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF +m (SF 6) 1 were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF +m (SF 6) n with m = 0−4. The structures of SF +5, SF + (SF 6) 1, SF +3 (SF 6) 1, and SF +5 (SF 6) 1 were investigated by ab initio molecular orbital calculations. For SF +5, the D3h geometry is found to be most stable and C4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures. 相似文献
19.
A new spectrophotometric flow-injection (FI) method is proposed for the determination of glucose based on the redox reaction of hydroquinone with iron(III). When a glucose solution containing quinone is passed through the immobilized glucose oxidase column introduced in FI system, quinone is reduced to hydroquinone by glucose. In the presence of 1,10-phenanthroline (phen), iron(III) is then quantitatively reduced by hydroquinone to iron(II) followed by the formation of iron(II)-phen complex ( λmax=510 nm). An FI peak observed at 510 nm corresponds to the concentration of glucose. The wide dynamic range for glucose was obtained in the range of 1×10 −6–1×10 −3 mol l −1 at a sampling rate of 24 h −1 and the detection limit (S/N=3) was 5×10 −7 mol l −1. Relative standard deviations were 0.78, 0.44 and 0.23% ( n=5) for 5×10 −6, 5×10 −5 and 5×10 −4 mol l −1 of glucose, respectively. The proposed method was successfully applied to the determination of glucose in control blood sera, human blood plasma and wine. 相似文献
20.
Investigation of the use of a single analytical procedure using the non-suppressed ion chromatographic method with direct spectrophotometric detection capable of determining eight oxoanions simultaneously is presented in this paper. Potassium phosphate was found to be the most suitable eluent for UV absorbance detection at 205 nm. Oxoanions AsO 3−3, SeO 2−3, AsO 3−4, VO −3, SeO 2−4, WO 2−4, MoO 2−4 and CrO 2−4 were detected at ng ml −1 levels with well separated peaks at retention time < 25 min. The working range is in the range ng ml −1 to 50 μg ml −1. The method is sufficiently sensitive to determine As (V), V(V), Mo(VI) and Cr(VI) anions (and NO −3) directly in a river water sample. The accuracy of these results was established by comparison with conventional atomic absorption methods. 相似文献
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