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51.
The vacuum-ultraviolet (VUV) pulsed-field ionization-photoelectron (VUV-PFI-PE) spectra of trans-1-bromopropene (trans-CH(3)CH[Double Bond]CHBr) and cis-1-bromopropene (cis-CH(3)CH[Double Bond]CHBr) have been measured in the energy region of 74 720-76 840 cm(-1). The simulation of fine structures observed in the origin VUV-PFI-PE vibrational bands of these molecules has provided the ionization energies (IEs) of trans-1-bromopropene and cis-1-bromopropene to be 74 779.3+/-2.0 cm(-1) (9.2715+/-0.0002 eV) and 75 140.2+/-2.0 cm(-1) (9.3162+/-0.0002 eV), respectively. The vibrational bands resolved in these VUV-PFI-PE spectra at energies 0-1700 cm(-1) above the IEs of trans-1-bromopropene and cis-1-bromopropene have been assigned based on theoretical vibrational frequencies and calculated Franck-Condon factors for the ionization transitions. 相似文献
52.
John T. W. Lai Frankie W. Lau Damon Robb Peter Westh Gerda Nielsen Christa Trandum Aase Hvidt Yoshikata Koga 《Journal of solution chemistry》1995,24(1):89-102
The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H2O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H2O. The values of the excess partial molar Gibbs energies for both DMSO and H2O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H2O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H2O molecules from exposure to the nonpolar alkyl groups of DMSO. 相似文献
53.
The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10−4–1.0×10−2 M H2PO4−. Anion corrections for interferences by Cl−, NO3− and SO42− were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions. 相似文献
54.
Structure and Reactivity of a Triazolo-benzodiazepine/Oxalyl Chloride Adduct Reaction of oxalyl chloride with N, N-dimethyl-{8-chloro-6-(0-fluorophenyl)- 4H, 11 H-[1,2,4]triazolo [1,5-α] [1,4]benzodiazepine}-2-carboxamide ( 6a ), the syn-thesis of which is described, leads to the cyclic adduct N, N-dimethyl-{2,12,12-trichloro-13a-(0-fluorophenyl)-11-oxo-10,11,12,13a-tetrahydro-5H, 9H-[1,3]oxazolo [3,2-d] [1,2,4]triazolo [1,5-a] [1,4]benzodiazepine}-7-carboxamide ( 7a ). Upon thermolysis 7a is partly reconverted to the starting diazepine 6a via loss of the elements of oxalyl chloride. Reduction of 7a with sodium borohydride also yields 6a in addition to its dihydro derivative 9 . Energetic treatment of 7a with sodium methoxide leads to the unexpected methoxydiazepines 10a and 10b , and mild treatment of 7a with sodium methoxide to the stereoselective formation of the two precursors of 10 , namely the chloromethoxy derivative 11 and the dimethoxy derivative 12 . Epimerization of 11 followed by nucleophilic substitution gives a mixture of two dimethoxy compounds, 12 and its epimer 14 . The configurational assignments of these derivatives are based upon X-ray analysis of 12 . A possible pathway for this unexpected substitution reaction is proposed. 相似文献
55.
Roland Achini 《Helvetica chimica acta》1981,64(7):2203-2218
The construction of new or novelly functionalized annulated and bridged tricylic compounds by two consecutive C,C-bond formations (a and b in la , Scheme 1) is described. In a first step, chloroalkyl-substituted aminonitriles yielded pyrrolidines 8 , 15a , 15b , 23 , 25 and piperidine 18 by carbanionic ring closure (Schemes 5, 6, 7 and 8). Subsequent Friedel-Crafts cyclization transformed the β-aminonitriles 8 , 15a , 15b , and 18 either directly or via their carboxylic acid derivatives to the indeno [1, 2-c]pyrrole, 2, 5-methano-3-benzazocine, benz [f]isoindoline and 1, 4-ethano-2-benzazapine skeletons 11 , 16a , 16b and 21 , respectively (Schemes 5, 6 and 7). By classical ring expansion reactions the pyrrolo [3, 4-c]isoquinoline and benzopyrano-[3, 4-c]pyrrole skeletons 28 resp. 31 were obtained from 11 (Scheme 9). 相似文献
56.
Alkyl ketene dimer (AKD) sizing of paper involves the redistribution of the wax over the fibre surface upon heating. The two
major mechanisms widely studied so far are the spreading of an autophobic precursor of molten AKD and AKD vapour transport
and re-deposition on the fibre surface. All previous work assumed that the transport of AKD vapour could be expressed by the
change of water contact angle with substrates that were exposed to the vapour. Information regarding the chemical composition
of the vapour phase above the AKD wax has not been found in the literature. In this work, a simple method for analysing the
chemical composition of the vapour is established. Our preliminary results indicated that the chemical composition of AKD
vapour in the temperature range of 75–80 °C is dominantly fatty acids. This suggests that the sizing effect by actual AKD
molecules via the vapour deposition mechanism is likely to be insignificant in this temperature range. This also implies that
fatty acids play a positive role in AKD sizing. The chemical stability of AKD in this temperature range is also studied. 相似文献
57.
A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method. 相似文献
58.
The fluxional molecule Os3(CO)7[P(OMe)3]5 has been prepared from OS3(CO)12 and P(OMe)3 by a combination of thermal and UV irradiation synthetic methods. An investigation by 31P and 13C NMR spectroscopy indicated that the mechanism of fluxionality in this compound probably involves the P(OMe)3 ligand of the Os(CO)3[P(OMe)3] unit moving from one equatorial site to the other via a trigonal twist mechanism. 相似文献
59.
This numerical simulation paper focuses on the adsorption/desorption of water in disordered mesoporous silica glasses (Vycor-like). The numerical adsorbent was previously obtained by off lattice method, and was shown to reproduce quite well the micro- and mesotextural properties of real Vycor, as well as morphological (pore size distribution) and topological (pore interconnections) disorder. The water-water interactions are described by the SPC model while water-silica interactions are calculated in the framework of the PN-TrAZ model. The water adsorption/desorption isotherms and the configurational energies are calculated by the Grand Canonical Monte Carlo simulation method. The low pressure results compare well with experiments, showing the good transferability of the intermolecular potential. It is shown that if the hysteresis loop observed in the adsorption/desorption isotherm is considered as a true phase transition (which is actually still an open question in the case of disordered porous materials), then it is possible to calculate the grand potential by applying the thermodynamic integration scheme. The grand potential is shown to be multivalued for low (subcritical) temperature, and continuous for high (supercritical) temperature. A coexistence point is found within the hysteresis loop, actually close to the vertical desorption line. Below the equilibrium chemical potential, the gaslike branch is stable whereas the liquidlike branch is metastable. The situation is reversed above the coexistence point. 相似文献
60.
Peter Wipf Roland Prevo Jost H. Bieri Gabriel Germain Heinz Heimgartner 《Helvetica chimica acta》1988,71(5):1177-1190
Thermal Generation and Reactions of (Benzylthio)-and (Arylthio)-Substituted Nitrile Ylides Thermolysis of 4-(benzylthio)- and 4-(arylthio)-1,3-oxazol-5(2H)-ones 6 , at 110–155° in the presence of dipolarophiles with activated C≡C, C?C, C?O, C?S, and N?N bonds, led to 5-membered cyclo-adducts and CO2 (cf. Schemes 3, 5-7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline-3-carboxylate ( 19 ) and ethyl pyridine-3-carboxylate( 22 ), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio-substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3-dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]-H shift to give 2-aza-1,3-butadienes of type 20 . The latter are trapped in a Diels-Alder reaction with ethyl propiolate (cf. Scheme 8). 相似文献