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41.
Guillard J Meth-Cohn O Rees CW White AJ Williams DJ 《Chemical communications (Cambridge, England)》2002,(3):232-233
The first calixhetarenes with more than one heteroatom in the constituent rings are prepared in one step by treatment of calix[4]furan 1a and calix[6]furan 1b with ethyl carbamate, thionyl chloride and pyridine to give 2, 3, 4 and 5, 6, 7 respectively; these products have been characterised by X-ray crystallography which reveals that in 2 all eight heteroatoms lie on one face of the macrocyle. 相似文献
42.
Pilar Jiménez Maria Victoria Roux JiŘi Kulhánek Otto Exner 《Structural chemistry》1996,7(5-6):375-381
The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements betweenT=270 K andT=338 K were carried out by DSC. From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono- and dimethoxy-benzoic acids have been completed. Theirf H
m
o
values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ·mol–1 was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy—the so-called buttressing effect—was evaluated (2–24 kJ· mol–1 for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the Car-O bond. 相似文献
43.
A fibre-optic sensor for continuous measurement of sulphur dioxide is described. It is based on the dynamic quenching of the fluorescence of a polynuclear aromatic hydrocarbon [benzo(b)fluoranthene] which is immobilized in silicone polymer. Sulphur dioxide is shown to be an efficient quencher; Stern-Volmer graphs are given which describe the relation between SO2 concentration and relative fluorescence. Detection limits are about 0.01% (v/v) SO2 in air; the useful range is from 0.01–6% (v/v). Other gases likely to occur in air were found to be inert, except for oxygen which also acts as a dynamic quencher. Its interference is negligible for SO2 levels below 6% in air at constant oxygen pressure, because the quenching efficiency of SO2 is about 26 times higher than that of oxygen. For varying oxygen levels, a two-sensor technique is suggested. 相似文献
44.
Summary. N′-Arylacetonitrilimines were generated from acetohydrazonyl chlorides and reacted with mercaptoalkanoic acids forming 4-aryl-5-oxo-3-thiahexanoic
acids. These were cyclized by reaction with dicyclohexyl carbodiimide yielding 2-acetyl-4-aryl-6H-1,3,4-thiadiazin-5-ones.
Received November 13, 2001. Accepted January 9, 2002 相似文献
45.
Otto Funk Lothar Schwabe Karl-Heinz Frömming 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(4):299-314
The purpose of the study was to examine the formation of inclusion compounds in the freeze-dried products obtained from aqueous solutions of nicotinic acid and -cyclodextrin (-CD), or heptakis (2,6-0-dimethyl)--cyclodextrin (DIMEB). The molar ratios used were 1:1 and 2:1. In addition two freezing temperatures (–40 and –196°C) and different secondary drying temperatures (+50 and +80°C) were used. Freeze-dried products with -CD obtained after low temperature freezing are of the same crystallographic structure as seen in a pure inclusion compound prepared by coprecipitation. Amorphous products were formed after fast freezing. The molar ratios of included nicotinic acid in the freeze-dried products vary — dependent on the preparation conditions — between 0.75:1 and 1:1. A factorial design proves that the included drug amount can be increased by enhancement of the amount of nicotinic acid used, by faster freezing, and by the combination of these two factors. The proof of inclusion formation was given by a combination of X-ray diffractography, differential scanning calorimetry, thermogravimetry and thermofractography.The freeze-dried preparations obtained with DIMEB were amorphous mixtures of the two components. No proof for inclusion of the nicotinic acid in the cyclodextrin cavity could be given. Higher (–40°C) or lower (–196°C) freezing temperatures and the running of the secondary drying process could not influence these results. The very low stability constant of the complex and steric reasons are responsible for this behavior. 相似文献
46.
Otto Röschel 《Journal of Geometry》1993,47(1-2):131-140
In part I we have studied a map of osculating elements of an affine Cayley-Klein (CK-) plane into the Lie algebra A4(2) of the aequiform transformations A4(2) of the given plane A2(, 2). If we use the real projective space P3() over A4(2) each osculating element defines a straight line in P3(). We now give a one parameter motion in A4(2) and study second order properties and their analogon in the Lie algebra and P3(), respectively. We show that the wellknown relationship between the points of the moving frame and the osculating circles of the point paths in the fixed frame may be interpreted as part of a quadratic map of certain straight Lines of P3(). An analogous result holds for the curvature of pairs of envelopes; the mapV induced in P3() than is contained in a cubic relationship of straight lines.
Herrn Professor Oswal Giering zum 60. Geburtstag gewidmet 相似文献
Herrn Professor Oswal Giering zum 60. Geburtstag gewidmet 相似文献
47.
A new computer controlled equipment for carrier concentration profile determination of silicon structures by a spreading resistance technique is presented. The required data and plots can easily be obtained by means of a new software package, which has been specially developed for this purpose. Measurements have been performed on different structures in order to verify the suitability of both the measuring system and the software package. The reproducibility has been found to be within 5% for the investigated structures. 相似文献
48.
Otto F. Hagena 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,17(3):157-158
This note reports on the first successfull experiments to generate silver clusters (N≦100) in supersonic nozzle flows. A mixture of argon/silver-vapor was used expanding from a conical nozzle (0.35 mm, 10° full cone angle, 17 mm long conical section). Source temperature and total pressure ranged up to 2200 K/300 kPa, and silver partial pressure up to 25 kPa. The data confirm the scaling laws developed to compare clustering of metals with that of rare gases. 相似文献
49.
50.
Jochen Triepel Prof. Dr. Hans-Hartwig Otto 《Monatshefte für Chemie / Chemical Monthly》1977,108(5):1085-1092
A semi-quantitative method for determining distances between a possible coordination centre and protons from LIS-NMR values is developed for the title compounds3, although these have four coordination points. This makes it possible to propose structures and conformations for the isomers of3.
Mit 4 Abbildungen
H.-H. Otto undH. Yamamura, Ann. Chem., im Druck. 相似文献
Mit 4 Abbildungen
H.-H. Otto undH. Yamamura, Ann. Chem., im Druck. 相似文献