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71.
A. Lainez M. M. Rodrigo Emmerich Wilhelm J. -P. E. Grolier 《Journal of solution chemistry》1992,21(1):49-65
Excess molar volumes V
E
and excess molar heat capacities C
P
/E
at constant pressure have been obtained, as a function of mole fraction x1, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (ClH2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V
E
of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x1>0.90). All the other systems show positive V
E
only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x1>0.87). The C
P
/E
at the respective minima, C
P
/E
(x1,min
), become more negative with increasing l, and the x1,min
values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of C
P
/E
against x1 with two minima and one maximum, the so-called W-shape curves.Dedicated to Professor A. Néckel on the occasion of his 65th birthday. Communicated in part at the XVIIèmes Journées de Calorimétrie, d'Analyse Thermique et de Thermodynamique Chimique, Ferrara, Italy, 27–30 October, 1986. 相似文献
72.
Results of voltammetric, potentiometric, chronoamperometric, ion transport, and extraction studies on neutral carrier based, plasticized poly(vinyl chloride) membranes are summarized. They unambiguously confirm that such bulk membranes dispose of immobile anionic sites. These fixed sites lead to a Donnan exclusion of other anions from the membrane and thus to a permselectivity for cations. The results are in perfect agreement with the predictions of earlier membrane models. A rigorous Poisson-Boltzmann analysis of macroscopic liquid membranes clearly indicates that space-charge at the membrane/solution interfaces does not influence the electrochemical properties and the ion-selectivity behavior at steady state. 相似文献
73.
Wurche F Sicking W Sustmann R Klärner FG Rüchardt C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(11):2707-2721
The effect of pressure on the oxidation of hydroarenes 3-9 with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ; 1 a) or o-chloranil (10), leading to the corresponding arenes, has been investigated. The activation volumes were determined from the pressure dependence of the rate constants of these reactions monitored by on-line UV/Vis spectroscopic measurements in an optical high-pressure cell (up to 3500 bar). The finding that they are highly negative and only moderately dependent on the solvent polarity (DeltaV( not equal ) = -13 to -25 in MTBE and -15 to -29 cm(3) mol(-1) in MeCN/AcOEt, 1:1) rules out the formation of ionic species in the rate-determining step and is good evidence for a hydrogen atom transfer mechanism leading to a pair of radicals in the rate-determining step, as was also suggested by kinetic measurements, studies of kinetic isotope effects, and spin-trapping experiments. The strong pressure dependence of the kinetic deuterium isotope effect for the reaction of 9,10-dihydroanthracene 5/5-9,9,10,10-D(4) with DDQ (1 a) can be attributed to a tunneling component in the hydrogen transfer. In the case of formal 1,3-dienes and enes possessing two vicinal C--H bonds, which have to be cleaved during the dehydrogenation, a pericyclic hydrogen transfer has to considered as one mechanistic alternative. The comparison of the kinetic deuterium isotope effects determined for the oxidation of tetralin 9/9-1,1,4,4-D(4)/9-2,2,3,3-D(4)/9-D(12) either with DDQ (1 a) or with thymoquinone 1 c indicates that the reaction with DDQ (1 a) proceeds in a stepwise manner through hydrogen atom transfer, analogously to the oxidations of 1,4-dihydroarenes, whereas the reaction with thymoquinone 1 c is concerted, following the course of a pericyclic hydrogen transfer. The difference in the mechanistic courses of these two reactions may be explained by the effect of the CN and Cl substituents in 1 a, which stabilize a radical intermediate better than the alkyl groups in 1 c. The mechanistic conclusions are substantiated by DFT calculations. 相似文献
74.
Max Winter Karl H. Schulte-Elte Alain Velluz Josef Limacher Wilhelm Pickenhagen Günther Ohloff 《Helvetica chimica acta》1979,62(1):131-134
Aroma Constituents of the Purple Passion Fruit. Two New Edulan Derivatives The isolation of (2R*, 4S*, 4aS*, 8aS*)-4,4a-epoxy-4,4a-dihydroedulan ( 1 ), and (2R*, 3S*, 8aS*)-3-hydroxyedulan ( 2 ), two new constituents of the purple passion-fruit (Passiflora edulis SIMS ), is reported. Racemic epoxide 1 was synthesized by oxidation of edulan 6 with peracidic acid, and racemate of alcohol 2 was obtained by reduction of ketone 7 , one of the chromic acid oxidation-products of edulan 6 . 相似文献
75.
The N,N-diisopropylphosphoramidites 10a and 10b of appropriately protected chiral diastereoisomers of d(T[P-18O]-A) ( 8a and 8b , resp.), chiral by virtue of the isotope 18O at the P-atom, have been synthesized. The 18O-isotope was incorporated by oxidation of the phosphite triester 3 with H2[18O]/I2. Separation of the diastereoisomers was accomplished by flash chromatography of the O-3′-deprotected phosphate triesters 5a/b . The absolute configuration at the chiral P-atom was deduced from the methylation products of the fully deprotected diastereoisomers 8a and 8b . Phosphinylation of 5a and 5b yielded the configurationally pure phosphoramidites 10a and 10b , respectively, which were then employed in solid-phase synthesis to yield the self-complementary oligomers d(G-A-G-T-(Rp)-[P-18O]-A-C-T-C) ( 13 ) and d(G-A-G-T-(SP)-[P-18O]-A-C-T-C) ( 14 ), respectively. 相似文献
76.
High-throughput experiments (HTE) result in large amounts of raw data that have to be evaluated for sample classification. Especially mass spectrometry, a widely used detection method in catalytic HTE applications, produces enormous amounts of data. In the past few years, in catalysts research, several test rigs based on mass spectrometric detection have been independently reported by different groups. In a typical HTE, the catalysts are tested sequentially; the recording of the scans, however, occurs continuously. For this reason, the scans of interest have to be extracted from the raw data, and scans belonging to the same sample have to be averaged in a tedious procedure before further processing. In this publication, we present our custom-designed software MS-Express (mass spectrometry data-extracting and -processing software), an efficient tool for HTE MS data evaluation. MS-Express not only sorts the data, it also establishes statistical significance with the help of reference and blank data and provides concise information about abundance and intensity distributions of expected peaks. A special feature is that the program also reports unexpected MS signals, which potentially lead to unexpected discoveries. 相似文献
77.
Sulfur Dioxide as Ligand and Synthon. XIII. Reactions of Isocyanide-tris(triphenylphosphane)nickel(0) Complexes with Sulfur Dioxide and N-p-tolylsulfinylamine Reactions of the isocyanide-tris(triphenylphosphane)-nickel(0) complexes [(RNC)Ni(PPh3)3] (R = tBu, Cy, PhCH2, p-TosCH2) with SO2 and p-TolNSO are described. The sulfur dioxide and N-p-tolylsulfinylamine complexes obtained by PPh3 ligand substitution have been characterized by means of i.r. and 31P n.m.r. spectra. The X-ray crystal structure of [(Ph3P)2(CyNC)Ni(SO2)] · 0.5 PhMe and (Ph3P)(tBuNC)Ni(η2-p-TolNSO) have been determined. 相似文献
78.
Bis(diphenylphosphano)alkane- and 1-Diphenylphosphano-2-(2-pyridino)ethane-N-arylsulfinylamine Nickel(0) Complexes Synthesis and properties of the bis(diphenylphosphano)alkane-N-phenyl-sulfinylamine-nickel(0) complexes [Ni{Ph2P(CH2)nPPh2}(PhNSO)] (n = 2 dppe, n = 3 dppp, n = 4 dppb) as well as of the 1-(diphenylphosphano)-2-(2-pyridino)ethane nickel(0) complexes [Ni(dpppe)2], [Ni(dpppe)(p-TolNSO)] and [Ni(dpppe)(PPh3)2] are described. These compounds have been characterized by i. r. and 31P n.m.r. spectroscopy. The N-arylsulfinylamine ligands are η2-(N, S)-side on coordinated. 相似文献
79.
Retrobiosynthetic analysis of the allergenic sesquiterpene lactone, anthecotuloide, suggested that this natural product could be formed either by head to head condensation of geranyl diphosphate with dimethylallyl diphosphate, or from farnesyl diphosphate (FPP), the accepted regular sesquiterpene precursor via the rearrangement of a germacranolide precursor. Isotopic labelling of anthecotuloide has now been achieved by feeding [1-(13)C]-glucose, [U-13C6]-glucose and [6,6-(2)H2]-glucose to aseptically grown plantlets of Anthemis cotula(family Asteraceae). Analysis of labelling patterns and absolute 13C abundances using quantitative 13C NMR spectroscopy showed that the isoprene building blocks of this sesquiterpene are formed exclusively via the MEP terpene biosynthetic pathway. This was supported by results from an experiment using [U-13C6]-glucose. A deuterium labelling experiment using [6,6-(2)H2]-glucose supported the original proposal and showed that anthecotuloide is formed from a non FPP precursor. Isotope ratio mass spectrometry suggested that there were two pathways for sesquiterpene biosynthesis in A. cotula. 相似文献
80.
Armin Dietrich Birgit Maas Wilhelm Messer Günther Bruche Volker Karl Astrid Kaunzinger Armin Mosandl 《Journal of separation science》1992,15(9):590-593
The characteristics of the new chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin are outlined and compared with permethyl- and perethyl-β-cyclodextrins. 相似文献