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11.
Mariana Ciureanu Victor E. Sahini Felicia Cornea Cornelia Cercasov Mihai Contineanu 《Magnetic resonance in chemistry : MRC》1981,15(2):148-151
The barriers to internal rotation about the C? N bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG?) increases in the series cinnamoylthiopiperidide<thiobenzoylpiperidide<phenylthioacetylpiperidide. This trend was discussed in terms of the electronic structure, using HMO calculations. For m-and p-substituted cinnamoylthiopiperidides the barriers were shown to increase with the electron withdrawing character of the substituent in the aromatic ring. 相似文献
12.
[reaction: see text] The 2,2,2-trichloroethyl (TCE) group was utilized as the first protecting group for aryl sulfates. Aryl sulfates, protected with the TCE group, were prepared in high yield by reacting phenols with chlorosulfuric acid TCE ester. Deprotection was accomplished using Pd/C-ammonium formate or with Zn-ammonium formate to give aryl sulfate monoesters in high yield. This approach to aryl sulfate synthesis was successfully applied to the construction of estrone sulfate derivatives, which could not be prepared by previous methodologies. 相似文献
13.
Martin P. Seah Felicia M. Green Ian S. Gilmore 《Journal of the American Society for Mass Spectrometry》2010,21(3):370-377
Measurements are described to evaluate the constitution of secondary ion mass spectra for both monatomic and cluster primary
ions. Previous work shows that spectra for different primary ions may be accurately described as the product of three material-dependent
component spectra, two being raised to increasing powers as the cluster size increases. That work was for an organic material
and, here, this is extended to (SiO2)
t
OH− clusters from silicon oxide sputtered by 25 keV Bi
n
+ cluster primary ions for n = 1, 3, and 5 and 1 ≤ t ≤ 15. These results are described to a standard deviation of 2.4% over 6 decades of intensity by the product of a constant
with a spectrum, H
SiOH/*, and a power law spectrum in t. This evaluation is extended, using published data for Si
t
+ sputtered from Si by 9 and 18 keV Au− and Au3−, with confirmation that the spectra are closely described by the product of a constant with a spectrum, H
Si*, and a simple spectrum that is an exponential dependence on t, both being raised to appropriate powers. This is confirmed with further published data for 6, 9, 12, and 18 keV Al− and Al2− primary cluster ions. In all cases, the major effect of intensity is then related to the deposited energy of the primary
ion at the surface. The constitution of SIMS spectra, for monatomic and cluster primary ion sources, is shown, in all cases,
to be consistent with the product of a constant with two component spectra raised to given powers. 相似文献
14.
Pier Luigi Barili Maria Camilla Bergonzi Giancarlo Berti Giorgio Catelani Felicia D'Andrea Francesco De Rensis 《Journal of carbohydrate chemistry》2013,32(9):1037-1049
ABSTRACT The title compound, previously unreported in either enantioform, and its 2,6-di-O-benzyl derivative have been synthesized through a stereocontrolled epimerization at C-2 of 6-O-protected methyl 3,4-O-isopropylidene-5-C-methoxy-β-D-galactopyranosides. The epimerization, performed through a high yielding sequence of oxidation-reduction owing to the cooperative role of the equatorial C-1 aglycon and the steric hindrance of the isopropylidene group, turned out to be completely diastereoselective. Whereas the unprotected L-ribo-hexos-5-ulose exists, as proved by NMR in D2O, in five main tautomeric forms in a ratio of about 4:2:2:1:1, only two anomeric 1,4-furanosic forms are present at equilibrium in its 2,6-di-O-benzyl derivative, in ratios ranging from 10:1 to 7:3, depending on the prevalence of D2O or CD3CN in the solvent mixture. 相似文献
15.
Pier Luigi Barili Giancarlo Berti Giorgio Catelani Felicia D'Andrea Francesco De Rensis Giampaolo Goracci 《Journal of carbohydrate chemistry》2013,32(8):1167-1180
Abstract The unreported title compound and its 2,6-di-O-benzyl derivative have been prepared from methyl β-D-galactopyranoside through a sequence involving the bisglycoside methyl 2,6-di-O-benzyl-5-O-methoxv-β-D-galactopyranoside 8, the precursor of L-orabino-hexos-5-ulose, that was converted to the L-lyxo series by inversion at C-3. The inversion was achieved in acceptable yields by selective triflation, followed by displacement with benzoate, and by an oxidation/reduction sequence. Whereas 2,5-di-O-benzyl-L-lyxo-hexos-5-ulose exists entirely as a mixture of the two anomeric 1,4-furanosic forms, the unprotected hexos-5-ulose involves at equilibrium in CD3CN/D2O at least eight tautomers, one of which is predominant. 相似文献
16.
Mihaela Badea Rodica Olar Valentina Uivarosi Dana Marinescu Victoria Aldea Stefania Felicia Barbuceanu George Mihai Nitulescu 《Journal of Thermal Analysis and Calorimetry》2011,105(2):559-564
Two new complexes having general formula VOL2·nH2O [(1) L: 5-hydroxyflavone, n = 1; (2) L: chrysin, n = 4] were synthesized and characterized. Based on IR and electronic data we concluded that studied flavones act as bidentate
ligands in complexes with metallic ion coordinated in a square-pyramidal stereochemistry. The thermal analysis (TG, DTA) elucidated
the composition and also the number and nature of the water molecules. The thermal behavior also indicated strong interactions
between oxovanadium (IV) and these oxygen donor ligands. 相似文献
17.
I. Ursu I. Apostol D. Bǎrbulescu I.N. Mihǎilescu M. Moldovan A.M. Prokhorov V.P. Ageev A.A. Gorbunov V.I. Konov 《Optics Communications》1981,39(3):180-185
The analysis of some new experimental data has proved that the evaporation of a stainless steel target in vacuum under the action of powerful TE-CO2 microsecond pulsed laser radiation is initiated on the initial spike or not at all. The minimum “tail” duration to get evaporation was deduced as a function of the temporal pulse shape characteristics and the metal thermophysical properties. The vaporisation process was accompanied by nonequilibrium heating of vapour clouds leading to the target surface shielding. Two self-regulated evolutions were recognised which were attributed to the intense vaporisation and the target evaporation by the UV plasma emitted radiation, respectively. 相似文献
18.
I. Ursu R. Alexandrescu V. Drăgănescu C. Grigoriu I. N. Mihăilescu I. Morjan A. M. Prokhorov N. V. Karlov A. S. Lagutchev A. N. Orlov Yu. N. Petrov 《Applied physics. B, Lasers and optics》1988,47(1):61-65
New experimental results are reported pointing to the possibility of a laser control of the resonant gases transit through capillaries in the Knudsen and intermediate regimes. 相似文献
19.
20.
Laura Felicia Matusevich Ezra Miller 《Proceedings of the American Mathematical Society》2006,134(5):1375-1381
Let be an integer matrix, and assume that the convex hull of its columns is a simplex of dimension not containing the origin. It is known that the semigroup ring is Cohen-Macaulay if and only if the rank of the GKZ hypergeometric system equals the normalized volume of for all complex parameters (Saito, 2002). Our refinement here shows that has rank strictly larger than the volume of if and only if lies in the Zariski closure (in ) of all -graded degrees where the local cohomology is nonzero. We conjecture that the same statement holds even when is not a simplex.