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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
3.
A calorimeter designed for studies of reactions in hydrofluoric acid has been constructed. Enthalpies of dissolution of KF in aqueous solutions of HF (from 1,05 N to 28,3 N) have been measured. 相似文献
4.
Balakin V Alexandrov VA Mikhailichenko A Flöttmann K Peters F Voss G Bharadwaj V Halling M Holt JA Buon J Jeanjean J LeDiberder F Lepeltier V Puzo P Heimlinger G Settles R Stierlin U Hayano H Ishihara N Nakayama H Oide K Shintake T Takeuchi Y Yamamoto N Bulos F Burke D Field R Hartman S Helm R Irwin J Iverson R Rokni S Roy G Spence W Tenenbaum P Wagner SR Walz D Williams S 《Physical review letters》1995,74(13):2479-2482
5.
P. Cloudy J. M. Létoffé P. Germain J. P. Bastide A. Bayol S. Blasquez R. C. Rao B. Gonzalez 《Journal of Thermal Analysis and Calorimetry》1991,37(11-12):2497-2506
Study and characterization of molecular complexes between cholesterol and beta cyclodextrin has been done using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (13C NMR). Whatever the value of the molar ratio cholesterol/βCD used during the preparation, the same compound is always obtained. Corresponding to a molar ratio 1/3 (cholesterol/βCD), this compound is a stable hydrate which, contrary toβCD, contains at room temperature a large amount of molecules of water. It can be dehydrated under low pressure but the thermal degradation occurs at 200°C (250°C forβCD). This implies that cholesterol is strongly bounded toβCD. 相似文献
6.
The mass spectra of aliphatic aldehydes which contain a cyclopropane group included in the polymethylenic chain, in some instances, show two intense peaks, called A and B that are not encountered either in other cyclopropane-containing aliphatic compounds or in other aliphatic aldehydes. The intensity of peaks A and B is strictly dependent upon the distance between cyclopropane and aldehyde. When the number x of methylene groups between the two functions is equal to 4 or higher than 10, peaks A and B are intense, but when x is equal to 7, the peaks are small.Specific labelling shows that ion A contains the atoms of the cyclopropane ring, the polymethylenic chain between the two functions and the aldehyde function. Ion B also contains the aldehyde function and results from the expulsion of the polymethylenic interfunctional chain to which a hydrogen atom of the other part of the molecule is added. This hydrogen atom arises, to an extent of about 60%, from the methylene of the cyclopropane ring. A mechanism is proposed in which cyclization of the molecular ion occurs; ion A is obtained by direct α-cleavage to the ether function in the cyclic ion; ion B results from alternative ether-cleavage causing opening of the carbo-ring. One hydrogen from the cyclopropane ring is transferred leading to the elimination of the interfunctional chain.The fact that formulas of ions A and B correspond to [CnH2n-3O]+ and that their intensities are dependent of x make questionable any structural determination established only by mass spectral examination of cyclopropane aldehydes. 相似文献
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Etude des enthalpies de dissolution A 298 K des fluorures alcalins dans les solutions aqueuses de HF
Enthalpies of solution of alkali fluorides in aqueous HF have been measured over a wide range of HF concentrations. 相似文献
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In the field desorption mass spectrometry of oligosaccharides, traces of contaminating salts in polar solvents decrease the detection sensitivity, and in some cases no ion could be detected in the molecular range. The present work shows that the addition of alkaline salts (NaI or KI) greatly increases the sensitivity, and cationized molecular ions are obtained. The influence of the molar ratio sugar/salt on the nature and relative intensity of the desorbed species has been studied on mixtures of α-D -trehalose and NaI. At the low salt ratio (100:1), high molecular weight clusters [X M + Na]+ are preferentially formed. At the high salt ratio (1:10), mixed clusters [M + NaI + Na]+, doubly charged ions [M + 2Na]2+ and monomeric cationized ions [M + Na]+ are observed along with salt clusters [NaI + Na]+ and [2NaI + Na]+. In the range of molar ratios sugar/salt of 10:1 to 1:1, the field desorption mass spectra exhibit a cationized ion [M + Na]+, which contributes more than 80% of Σ100. This cationization technique has been applied to the field desorption mass spectrometry of several oligosaccharides. In all cases, the salt effect causes the replacement of the [M + H]+ ion by a [M + C]+ ion. (Note: the term [M + C]+ and similar ones mean an association between the whole molecule studied (M) and an alkaline cation [C]+ ([K)]+, [Na]+, [Li]+).) Thus, di, tri- and tetrasaccharides exhibit intense [M + Na]+ ions in the presence of NaI and only a few fragment peaks are observed in their field desorption mass spectra. This technique has been applied successfully to the detection of the hexasaccharide ajugose in a natural sample of pentasaccharide, and has also allowed the unambiguous determination of the composition of a mixture of partially methylated trehaloses. The salt effects are dicussed in terms of selective adsorption on the emitter, pre-existing soluble complexes sugar-salt, interactions between these species in the electric field and dissociative desorption of ionic complexes. 相似文献